Root Ecology

Knowledge about the root system structure and the uptake efficiency of root orders is critical to understand the adaptive plasticity of plants towards salt stress. Thus, this study describes the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe NaCl stress on the level of root orders. Phenotypic root traits known to influence uptake processes, for example frequency of root orders, specific root area, cortical thickness, and xylem traits, did not change homogeneously throughout the root system, but changes after 6 months under 90 mM NaCl stress were root order specific. Chloride accumulation significantly increased with decreasing root order, and the Cl 2 concentration in lower root orders exceeded those in leaves. Water flux densities of firstorder roots decreased to <20% under salinity and did not recover after stress release. The water flux densities of higher root orders changed marginally under salinity and increased 2-to 6-fold in second and third root orders after short-term stress release. Changes in root order frequency, morphology, and anatomy indicate rapid and major modification of C. volkameriana root systems under salt stress. Reduced water uptake under salinity was related to changes of water flux densities among root orders and to reduced root surface areas. The importance of root orders for water uptake changed under salinity from root tips towards higher root orders. The root order-specific changes reflect differences in vulnerability (indicated by the salt accumulation) and ontogenetic status, and point to functional differences among root orders under high salinity.

Fine roots play an important role in the biogeochemical cycles of terrestrial ecosystems and are vital for understanding forest ecosystem functioning and services. Higher plant species diversity has been largely reported to increase aboveground community biomass, but how biodiversity affects fine-root production and the related mechanisms in forests remain unclear. In this study, we aim to answer two questions: (i) does fine-root production increase with tree species richness? (ii) Can this effect be explained by niche complementarity among species? We analyzed data from a large forest biodiversity experiment (BEF-China) with 5-year-old trees. Fine-root growth was measured as standing biomass and annual fine-root regrowth was estimated using ingrowth cores. Moreover, relative yield was calculated to test whether over-or under-yielding occurred when mixtures were compared with the average monoculture of the species included in the mixtures. We calculated functional diversity for fine-root (≤2 mm in diameter) traits by Rao's quadratic entropy index for each species mixture. The effects of manipulated tree species richness and identity on fine-root traits were analyzed with linear mixed-effects models. Mixed models were also used to test the relationships between tree species richness and fine-root standing biomass, annual regrowth and vertical heterogeneity.

Pedunculate (Quercus robur L.) and sessile (Q. petraea [Matt.] Liebl.) oaks are known to display different ecological requirements, particularly relative to root hypoxia induced by water-logging. Q. robur is more tolerant to hypoxia than Q. petraea. We designed an experiment aiming at identifying morphological and physiological responses to root hypoxia that might differ between the two species. Potted seedlings were submitted during seven weeks to a water-logging treatment with O 2 concentrations below 3 mg L -1 in the vicinity of roots. The treatment induced growth cessation in both species. Q. petraea displayed a lower tolerance to hypoxia as demonstrated by the higher number of seedlings suffering shoot dieback and leaf chlorosis as compared to Q. robur. This difference should be related to the high number of adventitious roots and hypertrophied lenticels that were formed in Q. robur, compared to Q. petraea. In the fine roots of the two species, the activity of pyruvate decarboxylase (PDC), the key enzyme of the fermentative pathway, was stimulated after 24 h of water-logging. Transcripts of PDC increased after 48 h of water-logging in Q. robur and not in Q. petraea. Interestingly, transcripts of haemoglobin (Hb) (possibly involved in the putative nitric oxide cycle) followed the same pattern of response than those of PDC. Enzymes of the sucrose degradation pathway displayed decreased activities after 3 weeks of water-logging, probably due to decreased carbohydrate availability. Alcohol dehydrogenase (ADH), sucrose synthase (Susy), and pyruvate kinase (PK) activities were higher in Q. robur after 3 weeks of water-logging. This study provided a set of markers characterizing the differences of tolerance to hypoxia between the two species for further studies on intra and inter-specific diversity. water-logging / hypoxia / adventitious root / hypertrophied lenticel / carbon metabolism Résumé -Différences de réponses morphologiques et physiologiques à l'ennoyage entre deux espèces sympatriques de chêne (Quercus petraea [Matt.] Liebl., Quercus robur L.). Les chênes pédonculé (Quercus robur L.) et sessile (Quercus petraea [Matt.] Liebl.) présentent des différences de tolérance à l'hypoxie racinaire induite par ennoyage, Q. robur étant plus tolérant que Q. petraea. Nous avons mené une expérience visant à identifier des différences inter-spécifiques dans les réponses morphologiques et physiologiques à l'hypoxie racinaire. Des semis en pots ont été soumis à un ennoyage de 7 semaines avec une concentration en O 2 maintenue en dessous de 3 mg L -1 au voisinage des racines. Le traitement a provoqué un arrêt de croissance chez les deux espèces. Q. petraea a montré une plus faible tolérance que Q robur, avec un nombre plus élevé de plants présentant un dessèchement de l'appareil aérien ainsi qu'une plus forte chlorose des feuilles. Cette différence pourrait être due au plus grand nombre de racines adventives et de lenticelles hypertrophiées formées au collet de Q. robur. Dans les racines fines des deux espèces, l'activité pyruvate décarboxylase (PDC), enzyme clef de la fermentation alcoolique, a été stimulée après 24 h d'ennoyage. Les transcrits de PDC ont augmenté après 48 h d'ennoyage uniquement chez Q. robur. De façon intéressante, les transcrits d'hémoglobine (Hb) (qui pourrait être impliquée dans la voie de signalisation de l'oxyde nitreux), ont suivi le même profil de réponse que ceux de la PDC. Les enzymes du catabolisme du saccharose ont présenté une diminution d'activité après 3 semaines d'ennoyage, probablement consécutivement à une baisse de la disponibilité en hydrates de carbone. Les activités alcool-déshydrogénase (ADH), saccharose-synthase (Susy), et pyruvate-kinase (PK), ont été plus fortes après 3 semaines d'ennoyage. Cette étude a fourni des marqueurs caractérisant des différences inter-spécifiques de tolérance, qui pourront être utilisés lors d'études ultérieures de diversité intra et inter-spécifique de traits liés la tolérance à l'hypoxie racinaire.

Background and Aims Mixed forest plantations are increasingly recognised for their role in mitigating the impacts of climate change and enhancing ecosystem resilience. Yet, there remains a significant gap in understanding the early-stage dynamics of species trait diversity and interspecies interactions, particularly in pure deciduous mixtures. This study aims to explore the timing and mechanisms by which trait diversity of deciduous species and competitive interactions influence yield, carbon allocation, and space occupation in mixed forests, both above- and belowground. Methods A forest inventory was conducted in planted monocultures, 2-species, and 4-species mixtures of European Acer, Tilia, Carpinus, and Quercus, representing a spectrum from acquisitive to conservative tree species. Competition effects were assessed with linear mixed-effects models at the level of biomass and space acquisition, including leaf, canopy, stem, and fine root traits. Key Results Early aboveground growth effects were observed six years post-planting, with significant biomass accumulation after eight years, strongly influenced by species composition. Mixtures, especially with acquisitive species, exhibited aboveground overyielding, 1.5- to 1.9-times higher than monocultures. Fine roots showed substantial overyielding in high diversity stands. Biomass allocation was species-specific and varied markedly by tree size, the level of diversity, and between acquisitive Acer and the more conservative species. No root segregation was found. Conclusions Our findings underscore the critical role of species trait diversity in enhancing productivity in mixed deciduous forest plantations. Allometric changes highlight the need to differentiate between (active) acclimations and (passive) tree size-related changes, but illustrate major consequences of competitive interactions for the functional relation between leaves, stem, and roots. This study points towards the significant contributions of both above- and belowground components to overall productivity of planted mixed-species forests.

Background and aims Hyperspectral imaging is becoming a key, high-throughput technique in plant research. However, its application to roots has not yet received sufficient attention. The aims of this study are to identify spectral features that distinguish fine roots from soil, non-woody roots of different species, and dead from living roots, and to identify appropriate analytical techniques. Methods Roots of Alopecurus pratensis (meadow foxtail) and Urtica dioica (nettle) and the rhizosphere were imaged in rhizoboxes in the wavelength range 400–1700 nm, covering both visible near- (VISNIR) and shortwave infrared (SWIR) regions. Principal Component Analysis, K-means clustering, and Generalised Linear Model, Partial Least Squares Discriminant Analysis, and Distributed Random Forest models were used to classify groups. Wavebands critical for classification were identified. Results Our results demonstrate the intricate nature of spectra clustering, highlighting the challenges in the VISNIR range and the promise of SWIR data for enhanced separability. While species differentiation is challenging, the determination of the living conditions of the roots is possible within the SWIR range. The analysis reveals the significance of specific spectral regions, notably those associated with water content and senescence, in distinguishing between living and dead roots. Water content regions (mainly 1245 nm and 1450 nm) were most important in discriminating between roots and soil. Conclusions This study highlights the potential of spectral analysis, particularly in the SWIR region, for distinguishing roots by species and vitality. Further efforts are needed to develop robust methods for mixed data sets containing roots of different species and degrees of vitality.

SummaryIn the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting‐edge, meaningful and integrated knowledge. Consideration of the below‐ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below‐ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from ...

Quercus robur L. and Quercus petraea (Matt.) Liebl. are sympatric oak species with different ecological requirements. Quercus robur is more tolerant to waterlogging than Q. petraea. This ecological divergence may play a role in the maintenance of the two species despite the absence of an insurmountable reproductive barrier between them. We predicted that the genetic architecture of traits related to waterlogging tolerance differs between the species. To gain insight into this architecture in the absence of genetic markers for waterlogging tolerance, we compared populations of seedlings of each species for diversity in the expression of quantitative phenotypic traits induced by severe hypoxia. To determine the capacity for hypertrophied lenticel formation, we applied gas-impermeable mastic to stems of seedlings. Two months after application, the mastic treatment had induced the formation of 3 (± 2) cm -2 hypertrophied lenticels in the absence of root hypoxia. Leaf epinasty during root hypoxia was an early predictor of seedling mortality. Four weeks of waterlogging resulted in greater epinasty in Q. petraea than in Q. robur, but fewer hypertrophied lenticels (16 ± 6 versus 21 ± 9 cm -2 ) and adventitious roots (2.7 ± 4.7 versus 5.2 ± 5.9). Differences between species in these traits were associated with differences in the frequencies of extreme phenotypes rather than with a generally higher tolerance to waterlogging in Q. robur seedlings.

Euphrates poplar (Populus euphratica Oliv.) is a woody species that is naturally distributed in the desert areas of some parts of Asia and Africa. Because of its outstanding features, it is a model plant to study environmental stress tolerance. This research was conducted from 2014 to 2016 in order to study the relationship between performance indices and ion concentrations. The cuttings of 12 ecotypes were collected from different climatic conditions in Iran. Salinity stress was applied using four levels of NaCl (75, 150, 225 and 300 mM) and one control sample (salt-free). The performance indices [diameter and height growth, biomass production; leaf, stem, root and total biomass] showed significant differences in salt levels and ecotypes. The ion concentrations showed significant differences in salt levels (except Ca 2+) and varied in different ecotypes. There was no significant difference in salt×ecotype interaction for most of the variables. The ecotypes, treatments, (salt levels) means of performance indices and ion concentrations were separated into different groups. Correlation coefficients showed that the concentration of macronutrients had positive correlations with performance indices, and that salt ions had negative correlations. Correlation coefficients also showed that the ion concentrations had synergistic or antagonistic effects on each other. The results of this study showed that the key mechanisms of salt tolerance in this specie include: exclusion of salt from the root, compartmentalization of Na + in plant tissue, preventing excessive reduction of K + absorption resulting in the maintenance of the K + /Na + balance.

Euphrates poplar (Populus euphratica Oliv.) is a woody species that is naturally distributed in the desert areas of some parts of Asia and Africa. Because of its outstanding features, it is a model plant to study environmental stress tolerance. This research was conducted from 2014 to 2016 in order to study the relationship between performance indices and ion concentrations. The cuttings of 12 ecotypes were collected from different climatic conditions in Iran. Salinity stress was applied using four levels of NaCl (75, 150, 225 and 300 mM) and one control sample (salt-free). The performance indices [diameter and height growth, biomass production; leaf, stem, root and total biomass] showed significant differences in salt levels and ecotypes. The ion concentrations showed significant differences in salt levels (except Ca2+) and varied in different ecotypes. There was no significant difference in salt×ecotype interaction for most of the variables. The ecotypes, treatments, (salt levels)...

The aim of this study is to determine the coarse root biomass and to reveal the relationship with some habitat and stand properties in the beech stands in Sinop. The study included 20 sample plots of natural pure beech stands in Sinop Forestry Chiefdom. Diameter at breast height, stand age, tree height and number of trees were measured and rooting profile (1x2m) in the plots was examined. Coarse roots (each depth classes with 30 cm depth. We collected soil samples from rooting profiles and analyzed some of the physical and chemical properties of soil. The soil of the study area has a high clay content, and it is nearly doubling for soils deeper than the 30 cm. The mean coarse root biomass is 16.7 ton/ha and about 93% of it is distributed in 0-30 cm depth. There was no difference between shadow and sunny aspects in terms of coarse root biomass. While coarse root biomass has significantly related to basal area, clay and sand content of the soil and available field capacity, there is no relationship with diameter, age, height and number of trees. Distribution of the coarse roots mostly close to soil surface within first 30 cm depth may be due to heavy textured soils. These data could be used for estimating the amount of coarse root biomass and distribution depth of beech forests close to sea level with heavy clay soils.

Maize is grown under a wide spectrum of soil and climatic conditions. Maize is moderately sensitive to salt stress; therefore, soil salinity is a serious threat to its production worldwide. Understanding maize response to salt stress and resistance mechanisms and overviewing management options may help to devise strategies for improved maize performance in saline environments. Here, we reviewed the effects, resistance mechanisms, and management of salt stress in maize. Our main conclusions are as follows: (1) germination and stand establishment are more sensitive to salt stress than later developmental stages. (2) High rhizosphere sodium and chloride decrease plant uptake of nitrogen, potassium, calcium, magnesium, and iron. (3) Reduced grain weight and number are responsible for low grain yield in maize under salt stress. Sink limitations and reduced acid invertase activity in developing grains is responsible for poor kernel setting under salt stress. (4) Exclusion of excessive sodium or its compartmentation into vacuoles is an important adaptive strategy for maize under salt stress. (5) Apoplastic acidification, required for cell wall extensibility, is an important indicator of salt resistance, but not essential for better maize growth under salt stress. (6) Upregulation of antioxidant defense genes and βexpansin proteins is important for salt resistance in maize. (7) Arbuscular mycorrhizal fungi improve salt resistance in maize due to better plant nutrient availability. (8) Seed priming is an effective approach for improving maize germination under salt stress. (9) Integration of screening, breeding and ion homeostasis mechanisms into a functional paradigm for the whole plant may help to enhance salt resistance in maize.

SummaryIn the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting‐edge, meaningful and integrated knowledge. Consideration of the below‐ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below‐ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from ...

The drivers underlying the development of deep root systems, whether genetic or environmental, are poorly understood but evidence has accumulated that deep rooting could be a more widespread and important trait among plants than commonly anticipated from their share of root biomass. Even though a distinct classification of "deep roots" is missing to date, deep roots provide important functions for individual plants such as nutrient and water uptake but can also shape plant communities by hydraulic lift (HL). Subterranean fauna and microbial communities are highly influenced by resources provided in the deep rhizosphere and deep roots can influence soil pedogenesis and carbon storage.Despite recent technological advances, the study of deep roots and their rhizosphere remains inherently time-consuming, technically demanding and costly, which explains why deep roots have yet to be given the attention they deserve. While state-of-the-art technologies are promising for laboratory studies involving relatively small soil volumes, they remain of limited use for the in situ observation of deep roots. Thus, basic techniques such as destructive sampling or observations at transparent interfaces with the soil (e.g., root windows) which have been known and used for decades to observe roots near the soil surface, must be adapted to the specific requirements of deep root observation. In this review, we successively address major physical, biogeochemical and ecological functions of deep roots to emphasize the significance of deep roots and to illustrate the yet limited knowledge. In the second part we describe the main methodological options to observe and measure deep roots, providing researchers interested in the field of deep root/rhizosphere studies with a comprehensive overview. Addressed methodologies are: excavations, trenches and soil coring approaches, minirhizotrons (MR), access shafts, caves and mines, and indirect approaches such as tracer-based techniques.

The relationship between functional trait and habitat environment across tree species provides critical information for understanding the strategy of resource acquisition and utilization of each tree species. Correspondingly, the purpose of this study was to elucidate the relationship between root tip morphology and habitat environment in a primary lowland dipterocarp forest. Methods We surveyed habitat environmental factors for 13 target species of Macaranga and Shorea, i.e., light condition, soil physical properties, and soil nitrogen (N) dynamics, and root tip morphology, including speci c root tip length (SRTL), root tip diameter (RTD), and root tip tissue density (RTTD) and analyzed their relationship considering their phylogenetic effect. Results The differences in SRTL and RTD between Macaranga and Shorea species were validated by the difference in environmental factors, i.e., light intensity and soil ammoni cation rate. With the phylogenetic effect in mind, we detected an interspeci c variation in SRTL, RTD, and RTTD in response to differences in environmental factors such as light intensity, soil physical properties, soil nitri cation, and N mineralization rates. Among the same species of the trees, the SRTL decreased with increasing light intensity and increased with increasing nitri cation rates, while the RTD exhibited an opposite trend. Conclusion We con rmed that the root tip morphology varies according to habitat environment in tropical tree species. However, the variation pattern was different than that of the temperate tree species, implying the existence of factors that determine the direction of root tip morphological variation in response to environmental factors.

Aims The relationship between functional trait and habitat environment across tree species provides critical information for understanding the strategy of resource acquisition and utilization of each tree species. Correspondingly, the purpose of this study was to elucidate the relationship between root tip morphology and habitat environment in a primary lowland dipterocarp forest. Methods We surveyed habitat environmental factors for 13 target species of Macaranga and Shorea, i.e., light condition, soil physical properties, and soil nitrogen (N) dynamics, and root tip morphology, including specific root tip length (SRTL), root tip diameter (RTD), and root tip tissue density (RTTD) and analyzed their relationship considering their phylogenetic effect. Results The differences in SRTL and RTD between Macaranga and Shorea species were validated by the difference in environmental factors, i.e., light intensity and soil ammonification rate. With the phylogenetic effect in mind, we detecte...

Aims Specific root respiration (RR S) is a key root trait, determining i.e. nutrient foraging and uptake efficiencies. However, a considerable uncertainty exists regarding the effects of storage time and conditions on RR S measurements. Methods Fine root CO 2 efflux rates of three plant types (tree seedling Carpinus betulus, legume Pisum sativum, grass Lolium perenne) were measured as depending on storage time (30-1440 min post-rinsing) and conditions (i.e. attached to plant, warm and cold water storage, and storage under dry conditions). Results Short-term storage conditions (30 min) had a significant effect on measured RR S rates, in specific, RR S rates of all three species were significantly lower under dry storage. Irrespective of plant species or temperature, storage of excised roots in water did not affect RR S for 300 min,. RR S measurements remained stable for 1 day if roots were stored cold. Conclusions Our results have important implications on measurement routines of RR S-a generally understudied root trait. Henceforth it seems reasonable to collect roots in the field and transport them, hydrated but even uncooled, to the laboratory for subsequent measurements for at least 300 min post-rinsing.

Ten permanent 15 m transects previously established in two oak/saw palmetto scrub stands burned in December 1986, while two transects remained unburned. We sampled vegetation in the > 0.5 m and < 0.5 m layers on these transects at 6, 12, 18, 24, and 36 months postburn and determined structural features of the vegetation (height, % bare ground, total cover). We analyzed vegetation data from each sampling by height layer using detrended correspondence analysis ordination. Vegetation data for the > 0.5 m layer for the entire time sequence were combined and analyzed using detrended correspondence analysis ordination. Soils were sampled at 6, 12, 18, and 24 months postburn and analyzed for pH, conductivity, organic matter, exchangeable cations (Ca, Mg, K, Na), NO3-N, NH4-N, AI, available metals (Cu, Fe, Mn, Zn), and PO4-P. Shrub species recovered at different rates postfire with saw palmetto reestablishing cover >0.5 m within one year, but the scrub oaks had not returned to prebum cover >0.5 m in 3 years after fire. These differences in growth rates resulted in dominance shifts after fire with saw palmetto increasing relative to the scrub oaks. Such shifts were not uniform across the scrub gradient. Mixed oak/saw palmetto-dominated transects changed the most and recovered more slowly than either oak or saw palmetto-dominated transects. Distances between preburn and successive postburn locations in ordination space appear to be a useful index of this recovery. In mature scrub, ordination of the > 0.5 m layer reflected the environmental gradient from wet to dry.

Elevated atmospheric carbon dioxide (CO 2) often stimulates the growth of fine roots, yet there are few reports of responses of intact root systems to long-term CO 2 exposure. We investigated the effects of elevated CO 2 on fine root growth using open top chambers in a scrub oak ecosystem at Kennedy Space Center, Florida for more than 7 years. CO 2 enrichment began immediately after a controlled burn, which simulated the natural disturbance that occurs in this system every 10-15 years. We hypothesized that (1) root abundance would increase in both treatments as the system recovered from fire; (2) elevated CO 2 would stimulate root growth; and (3) elevated CO 2 would alter root distribution. Minirhizotron tubes were used to measure fine root length density (mm cm À2) every three months. During the first 2 years after fire recovery, fine root abundance increased in all treatments and elevated CO 2 significantly enhanced root abundance, causing a maximum stimulation of 181% after 20 months. The CO 2 stimulation was initially more pronounced in the top 10 cm and 38-49 cm below the soil surface. However, these responses completely disappeared during the third year of experimental treatment: elevated CO 2 had no effect on root abundance or on the depth distribution of fine roots during years 3-7. The results suggest that, within a few years following fire, fine roots in this scrub oak ecosystem reach closure, defined here as a dynamic equilibrium between production and mortality. These results further suggest that elevated CO 2 hastens root closure but does not affect maximum root abundance. Limitation of fine root growth by belowground resources-particularly nutrients in this nutrient-poor soil-may explain the transient response to elevated CO 2 .

In Mayan culture, the world tree is depicted as a large Kapok or Ceiba tree (Ceiba pentandra), with branches that reach into the sky and touch the heavens (McDonald, 2016). The trunk intersects the earthly forest, while the roots extend deep below ground. Roots reach into the underworld, Xibalba, connecting the physical world to celestial and subterranean spiritual realms. Inside caves of Quintana Roo, Mexico, a physical representation of the world tree can be seen alongside ceremonial altars, sculptures, pots, and tools: tree roots commonly emerge from the ceilings and walls of caves, linking the above-and belowground environments. In contrast to the focus on archaeological studies within these caves, the roots have remained understudied, despite being photographed and noted in journal articles, new stories, and blog posts. Because of this, the importance of the roots is sometimes disregarded, particularly when a cave is commercialized for tourism, during which roots are often cut, potentially harming the associated tree on the surface. This can be particularly problematic for trees that rely on deep water sources within a seasonally dry ecosystem. Seasonally dry and subhumid tropical forests are among the most threatened of the global tropical forests. Quite understudied compared to their wet counterparts, these tropical forests are critical centers of biodiversity and play an important role in global carbon cycling (Poulter et al., 2014; Sánchez-Azofeifa et al., 2005). In order to be successful in ecosystems with seasonal dry periods and high potential evapotranspiration, plants must have physiological adaptations to acquire water or reduce water loss. Deep rooting is an advantageous trait because it can expand a plant's search for water and enable it to reach reliable water at depth (Casper, Schenk, & Jackson, 2003). The occurrence of deep roots is predicted to be more common in dry or subhumid regions, yet, they remain understudied in these types of locations (Schenk & Jackson, 2005). Studying deep roots has obvious limitations because of the inability to access them directly without disturbance (Maeght, Rewald, & Pierret, 2013). Major excavations are costly and generally preclude physiological measurements. However, cave systems that exist close to the surface offer a unique opportunity to study deep roots directly. In addition, when caves are associated with water, this is where tree access to deep water may be expected (Bleby, McElrone, & Jackson, 2010). Although rooting depth in karst environments may be restricted by overlying bedrock, it is not uncommon for trees to grow through preexisting fissures in the bedrock to reach reliable

Salinity is a global agricultural problem, resulting in a significant reduction in the plantation areas and the crop yields, especially in arid and semiarid regions. e date palm is relatively salt-tolerant plant species, although the nature of salt tolerance is poorly understood. In this study, the salt stress responses of a salt-tolerant "Umsila" was compared with salt-susceptible "Zabad" date palm cultivars. Various physiological parameters, plant-water relations, and anatomical characteristics were analyzed. e results revealed that although salinity has negatively affected both cultivars, Umsila exhibited more stable photosynthesis than Zabad as reflected by the quantum yield (Qy) and the stomatal conductance (GS). Similarly, Umsila showed a more dynamic root system and efficient water relations than Zabad as demonstrated by the leaf water potential (LWP) and relative water content (RWC) during salinity. Umsila also accumulated greater abundances of soluble sugars, potassium (K +), calcium (Ca +2), proline, glycine betaine, and lignin and formed extra layers of Casparian strips in the root tissues when the seedlings were grown under saline conditions. Together, the results obtained from this study have offered some insights into the salt tolerance mechanisms in the date palm.

Uncertainty surrounds belowground plant responses to rising atmospheric CO 2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability. We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11 yr of elevated atmospheric CO 2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using groundpenetrating radar and total root biomass using soil cores. Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO 2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes. Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO 2. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO 2. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO 2 enrichment.

1. Plant communities show two general responses to gradients of soil resources: a decrease in species richness at high levels of resource availability and an associated shift in species composition from small and slow-growing species to large and fast-growing species. Models attempting to explain these responses have usually focused on a single pattern and provided contradicting predictions concerning the underlying mechanisms. 2. We use an extension of Tilman's resource competition model to investigate the hypothesis that both patterns may originate from the size-asymmetric nature of light exploitation by competing plants. The only mechanism producing changes in species richness and species composition in our model is mortality due to competition. 3. Under the framework of the model, asymmetric light exploitation is a necessary and sufficient condition to obtain the empirically observed responses of species richness and species composition to soil resource gradients. This theoretical result is robust to relaxing the simplifying assumptions of the model. 4. Our model shows that the traits enhancing competitive superiority depend on the mode of resource exploitation: under symmetric exploitation, competitive superiority is achieved by tolerance of low resource levels, while under asymmetric exploitation, it is achieved by the ability to grow fast and attain a large size. This result indicates that a long-standing debate concerning the traits that enhance competitive superiority in plant communities (the 'Grime-Tilman debate') can be reduced into a single parameter of our modelthe degree of asymmetry in resource competition. 5. The model also explains the observed shift from below-ground to above-ground competition with increasing productivity, the associated increase in the asymmetry of competitive interactions and the increasing likelihood of competitive exclusion under high levels of productivity. None of these patterns could be obtained under symmetric competition in our model. 6. Synthesis. The ability of the model to explain a wide range of observed patterns and the robustness of these predictions to its simplifying assumptions suggest that the size asymmetry of competition for light is a fundamental factor in determining the structure and diversity of plant communities.

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Investigating the relationship between neighbor root biomass and belowground competition: field evidence for symmetric competition belowground.-Oikos 90: 311-320. Little is known about how small-scale variation in neighbor biomass can influence the strength of root competition experienced by an individual plant. In this study, modified root exclusion tubes were used to vary the accessibility of the soil space surrounding Amaranthus retroflexus target plants to the neighboring plants. A gradient of root accessibility was created by drilling varying numbers of holes into standard root exclusion tubes, made of 15 cm diameter PVC pipe. Belowground competitive intensity, defined as biomass reduction due to root interactions alone, relative to growth in the absence of neighbors, was then measured along the resulting gradient of neighbor root densities. At low neighbor root abundances the strength of belowground competition was proportional to neighbor root biomass, consistent with prior evidence that belowground competition is symmetric. If belowground competition were asymmetric, neighbor roots should have had little effect on target plants when they are rare relative to those of the target plant. At higher neighbor root abundances, belowground competitive intensity should increase rapidly. The strong relationship found between neighbor root biomass and belowground competitive intensity suggests relatively small variations in root biomass could lead to large variations in belowground competition. Reduced belowground competition in areas with low root biomass could have important implications for the establishment and growth of poor belowground competitors, suggesting a mechanism by which species coexistence may occur despite extremely intense root competition.

Tree root systems are inherently dynamic in their distribution within a soil volume. Analysis of tree root system space occupation through time can improve not only our implicit understanding of a virtually hidden portion of a plant, but influence future management decisions through a more thorough understanding of root placement within a soil volume. We compared root standing crop populations of four ornamental tree species including Acer rubrum L. 'Franksred' (Acer), Carpinus betula L. 'Columnaris' (Carpinus), Gleditsia tricanthos L. var. inermis 'Skycole' (Gleditsia), and Quercus rubra L. 'Rubrum' (Quercus) grown in a nursery mix substrate within large 57-L containers using an X-ray computed tomography (CT) approach through time. Individual root identification was performed manually on two-dimensional slices of CT scans. Our data show high variation in species total root number through time with Carpinus exhibiting the largest root population throughout the study period. However, species exhibited differences in root distribution patterns as exemplified by the shallow and horizontally more uniform rooting pattern of Acer in comparison with the highly plastic root distribution in space through time in Gleditsia. Root frequencies within 1-mm root diameter class distributions shifted by species with the most drastic differences found between high frequencies of relatively small diameter roots in Acer vs. pronounced shifts in dominate root diameter size class as found in Gleditsia and lesser so in Carpinus during a growing season. Our findings demonstrate differences in whole tree root systems space occupation non-destructively through time and highlight a disparity in how species fill a container volume during growth.

C. Fassio, R. Cautin, A. G. Perez-Donoso, M. Castro, and C. Bonomelli. Comparative branching order and root anatomy of clonal and seed-grown avocado trees (Persea americana Mill.). Int. J. Agric. Nat. Resour. 134-144. Characterizing roots according to their branching order and anatomy is a useful approach for identifying functional differences within and among root systems. In this study, the root branching order and the anatomy of each root order (stele and cortex area) were examined in two-year-old "Duke 7" avocado (Persea americana Mill.) trees propagated by seed and by clonal techniques. The root systems were found to have three different root orders that exhibited differences in the occurrence of secondary xylem. Fine roots (first-and second-order roots) presented only primary growth, whereas the main roots (third-order roots) exhibited secondary growth. Transverse sections of roots from the different orders showed pentarch, hexarch or heptarch tracheal element distributions. Newly emerged, long, unbranched pioneer roots were observed only in the clonal trees and showed particular anatomical features, such as a larger diameter and a proportionally greater cortex area than other roots, as well as primary growth. Additionally, significant differences were found between clonal and seedling trees in the stele area of third-order roots; clonal propagation resulted in larger stele areas in this type of root. Our results suggest that propagation methods influence the presence of new pioneer roots and the anatomy of third-order roots; clonal root systems branch more extensively than seed-grown root systems and develop a vascular system with a larger transport capacity.

We compiled data from 149 paired observations from 43 publications and performed a meta-analysis to evaluate the variability of trees’ fine root trait responses under various global soil warming experiments. The impacts of warming magnitude, soil depth, and different tree species (deciduous vs. coniferous), on the responses of fine root biomass (FRB), and fine root morphology were assessed in this study. Our results confirmed that soil warming increased FRB while having no significant effect on fine root morphological traits, such as specific root length (SRL), specific root area (SRA), and diameter (D). The effect of warming on FRB decreased significantly at higher warming magnitude. The effect of tree species was also evident in the response of FRB to soil warming magnitude. Furthermore, warming effects on SRA and D increased in deeper soil horizons. The present meta-analysis provides an improved understanding of trees’ fine roots and the tree species-specific adaptive strategy un...

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

SummaryIn the context of a recent massive increase in research on plant root functions and their impact on the environment, root ecologists currently face many important challenges to keep on generating cutting‐edge, meaningful and integrated knowledge. Consideration of the below‐ground components in plant and ecosystem studies has been consistently called for in recent decades, but methodology is disparate and sometimes inappropriate. This handbook, based on the collective effort of a large team of experts, will improve trait comparisons across studies and integration of information across databases by providing standardised methods and controlled vocabularies. It is meant to be used not only as starting point by students and scientists who desire working on below‐ground ecosystems, but also by experts for consolidating and broadening their views on multiple aspects of root ecology. Beyond the classical compilation of measurement protocols, we have synthesised recommendations from ...

The effects of changes in auxin transport in response to different osmotic potentials (Ψo) were analyzed in the roots and leaves of two leguminous species with different degrees of salt tolerance: the halophyte Prosopis strombulifera (Lam.) Benth. and the glycophyte Glycine max L. The potentials were generated with sodium chloride (NaCl), sodium sulfate (Na 2 SO 4), and the iso-osmotic mixture of both salts (NaCl + Na 2 SO 4). The values evaluated were −1, −1.8, and −2.6 MPa for P. strombulifera, and −0.47, −0.69, and −0.87 MPa for G. max. In addition, the plants were sprayed with 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor. The parameters measured included root length, shoot height, number of leaves, relative membrane permeability in roots, and endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and zeatin (Z). Significant responses were observed at the lowest potentials evaluated (−2.6 MPa for P. strombulifera and −0.89 MPa for G. max). Treatment with Na 2 SO 4 inhibited plant growth more than the others, increased the relative membrane permeability, and enhanced ABA production to its highest levels. These toxic effects were slightly reversed in the presence of iso-osmotic mixture. TIBA brought about impaired development in shoots and roots, the highest values for membrane permeability, alterations in the distribution of endogenous ABA, IAA, and Z, as well as harmful effects on the growth response of both species. In general, the alterations in auxin transport intensified the effects of salinity, which confirms the essential role of this mechanism in plants under salt stress or in normal, non-stressful conditions.

The drivers underlying the development of deep root systems, whether genetic or environmental, are poorly understood but evidence has accumulated that deep rooting could be a more widespread and important trait among plants than commonly anticipated from their share of root biomass. Even though a distinct classification of "deep roots" is missing to date, deep roots provide important functions for individual plants such as nutrient and water uptake but can also shape plant communities by hydraulic lift (HL). Subterranean fauna and microbial communities are highly influenced by resources provided in the deep rhizosphere and deep roots can influence soil pedogenesis and carbon storage.Despite recent technological advances, the study of deep roots and their rhizosphere remains inherently time-consuming, technically demanding and costly, which explains why deep roots have yet to be given the attention they deserve. While state-of-the-art technologies are promising for laboratory studies involving relatively small soil volumes, they remain of limited use for the in situ observation of deep roots. Thus, basic techniques such as destructive sampling or observations at transparent interfaces with the soil (e.g., root windows) which have been known and used for decades to observe roots near the soil surface, must be adapted to the specific requirements of deep root observation. In this review, we successively address major physical, biogeochemical and ecological functions of deep roots to emphasize the significance of deep roots and to illustrate the yet limited knowledge. In the second part we describe the main methodological options to observe and measure deep roots, providing researchers interested in the field of deep root/rhizosphere studies with a comprehensive overview. Addressed methodologies are: excavations, trenches and soil coring approaches, minirhizotrons (MR), access shafts, caves and mines, and indirect approaches such as tracer-based techniques.

A sizeable number of scientists and funding organisations are of the opinion that the relevance of plant physiological ecology as an important discipline has declined to the point that it is no longer considered as one of the important topics of ecological research. Plant physiological ecology is typically associated with the autecological plant research conducted during the latter portion of the 20th century or, even worse, simply with gas exchange measurements. However, taking a closer look, it becomes obvious that, by focusing on the intermediate integration levels (individuals, populations), this discipline represents an essential link between the high integration levels (communities, ecosystems, biosphere) and the disciplines at the bottom of the complexity hierarchy (physiology, molecular biology). In this paper we show that the principal question of all ongoing community and ecosystem level research-What is the mechanistic background of vegetation composition, biodiversity structure and dynamics and how is this linked to fluxes of matter at the community and higher levels of organisation?-can only be answered if the mechanism of interactions between the relevant organisms are understood. In consequence, the classical discipline of plant physiological ecology will continuously develop into a truly interdisciplinary experimental ecology of interactions and its importance will rather increase than diminish. Promising activities of this kind are already underway. Scientists needed for this new direction should have a rather broad scientific perspective, including knowledge and experience in fields outside of typical ecological research, instead of being specialists for single ecophysiological aspects.

The responses of aboveground parts of the forest to changes in environmental factors and stand age is well studied, but the same is not true for the belowground parts of the forest. Two plantation black locust (Robinia pseudoacacia L.) forest sites were taken in the Loess Plateau of China, one in the drier, infertile, more sandy area of the middle Loess Plateau, and another in the wetter, fertile, more clay-filled area of the southern Loess Plateau. At each site, both a younger (8-year-old) plantation stand and an older (30-year-old) plantation stand were included to study the effects of soil physicochemical properties and stand age on the fine root (<2 mm) biomass and vertical distribution of black locust forests. Root samples were taken with soil cores to a depth of 100 cm. The fine root biomass decreased from the middle site to the southern site for both stand ages, as expected, and the decrease could be due to a higher fine root N concentration associated with a higher fine root turnover rate at the southern site. There was a similar rooting pattern, though not deeper, in the drier, sandy site as predicted based on soil water infiltration and evaporation demands. The different effects of stand characters (e.g., tree density, tree height) on the fine root distribution as compared with the environmental properties may contribute partly to the similar pattern found in the two sites. The fine root biomass increased with stand age in both sites. In contrast to the evident difference in fine root biomass, there was no clear trend in the fine root vertical distribution pattern with stand age. Our results indicate that fine roots are likely to respond to changes in soil physicochemical properties and stand age by changing fine root biomass rather than by varying rooting pattern.

The urban environment is stressful and trees experience multiple stresses, including drought, flooding, and extreme heat, all of which are likely to increase under future climate warming and increasing urbanisation. In the selection of tree species to maximise ecosystem services, tolerance to site characteristics such as flooding and severe drought is of critical importance. This study evaluated the suitability of a rare species, Alnus subcordata C.A. Mey (Caucasian alder) from the Hyrcanian forests of southern Azerbaijan, for its functionality as an urban tree. A total of 48 pot-grown, two-year-old saplings of A. subcordata were tested in a greenhouse experiment using a complete randomised block design. Each block contained four replicates of three treatments (waterlogging, drought, control), with 16 plants per treatment. Height differences between treatments were measured, and water status was estimated by determination of midday leaf water potential (Ψ L) and stomatal conductance (g s). To estimate drought tolerance reaction in the treatments, leaf water potential at turgor loss (Ψ P0) was used together with broken-stick modelling of water status over time. There was a significant difference in tree height between the different treatments. In the drought treatment, A. subcordata plants showed no height increase, while plants in both the waterlogged and control treatments increased in height during the nine-week experiment. Over 63 days of flooding, plant water status was slightly more negative in the waterlogging treatment, but did not deviate essentially from the control. In the drought treatment, plant water status rapidly deviated from the control. There was a significant difference in Ψ P0 between treatments, with drought-treated plants showing the lowest value (−2.31 MPa). This study demonstrated that A. subcordata has limited tolerance to drought and seems to rely more on water loss-avoiding strategies. However, the species may be usable at periodically waterlogged sites, due to its high tolerance to flooding. It could therefore be recommended for wet urban environments and stormwater management facilities, for which reliable guidance on suitable trees is currently lacking.

The root economics spectrum (RES), a common hypothesis postulating a tradeoff between resource acquisition and conservation traits, is being challenged by conflicting relationships between root diameter, tissue density (RTD) and root nitrogen concentration (RN). Here, we analyze a global trait dataset of absorptive roots for over 800 plant species. For woody species (but not for non-woody species), we find nonlinear relationships between root diameter and RTD and RN, which stem from the allometric relationship between stele and cortical tissues. These nonlinear relationships explain how sampling bias from different ends of the nonlinear curves can result in conflicting trait relationships. Further, the shape of the relationships varies depending on evolutionary context and mycorrhizal affiliation. Importantly, the observed nonlinear trait relationships do not support the RES predictions. Allometry-based nonlinearity of root trait relationships improves our understanding of the ecolo...

Elevated atmospheric carbon dioxide (CO 2) often stimulates the growth of fine roots, yet there are few reports of responses of intact root systems to long-term CO 2 exposure. We investigated the effects of elevated CO 2 on fine root growth using open top chambers in a scrub oak ecosystem at Kennedy Space Center, Florida for more than 7 years. CO 2 enrichment began immediately after a controlled burn, which simulated the natural disturbance that occurs in this system every 10-15 years. We hypothesized that (1) root abundance would increase in both treatments as the system recovered from fire; (2) elevated CO 2 would stimulate root growth; and (3) elevated CO 2 would alter root distribution. Minirhizotron tubes were used to measure fine root length density (mm cm À2) every three months. During the first 2 years after fire recovery, fine root abundance increased in all treatments and elevated CO 2 significantly enhanced root abundance, causing a maximum stimulation of 181% after 20 months. The CO 2 stimulation was initially more pronounced in the top 10 cm and 38-49 cm below the soil surface. However, these responses completely disappeared during the third year of experimental treatment: elevated CO 2 had no effect on root abundance or on the depth distribution of fine roots during years 3-7. The results suggest that, within a few years following fire, fine roots in this scrub oak ecosystem reach closure, defined here as a dynamic equilibrium between production and mortality. These results further suggest that elevated CO 2 hastens root closure but does not affect maximum root abundance. Limitation of fine root growth by belowground resources-particularly nutrients in this nutrient-poor soil-may explain the transient response to elevated CO 2 .

The effects of changes in auxin transport in response to different osmotic potentials (Ψo) were analyzed in the roots and leaves of two leguminous species with different degrees of salt tolerance: the halophyte Prosopis strombulifera (Lam.) Benth. and the glycophyte Glycine max L. The potentials were generated with sodium chloride (NaCl), sodium sulfate (Na 2 SO 4), and the iso-osmotic mixture of both salts (NaCl + Na 2 SO 4). The values evaluated were −1, −1.8, and −2.6 MPa for P. strombulifera, and −0.47, −0.69, and −0.87 MPa for G. max. In addition, the plants were sprayed with 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor. The parameters measured included root length, shoot height, number of leaves, relative membrane permeability in roots, and endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and zeatin (Z). Significant responses were observed at the lowest potentials evaluated (−2.6 MPa for P. strombulifera and −0.89 MPa for G. max). Treatment with Na 2 SO 4 inhibited plant growth more than the others, increased the relative membrane permeability, and enhanced ABA production to its highest levels. These toxic effects were slightly reversed in the presence of iso-osmotic mixture. TIBA brought about impaired development in shoots and roots, the highest values for membrane permeability, alterations in the distribution of endogenous ABA, IAA, and Z, as well as harmful effects on the growth response of both species. In general, the alterations in auxin transport intensified the effects of salinity, which confirms the essential role of this mechanism in plants under salt stress or in normal, non-stressful conditions.

A plant phenotyping approach was applied to evaluate growth rate of containerized tree seedlings during the precultivation phase following seed germination. A simple and affordable stereo optical system was used to collect stereoscopic red-green-blue (RGB) images of seedlings at regular intervals of time. Comparative analysis of these images by means of a newly developed software enabled us to calculate (a) the increments of seedlings height and (b) the percentage greenness of seedling leaves. Comparison of these parameters with destructive biomass measurements showed that the height traits can be used to estimate seedling growth for needle-leaved plant species whereas the greenness trait can be used for broad-leaved plant species. Despite the need to adjust for plant type, growth stage and light conditions this new, cheap, rapid, and sustainable phenotyping approach can be used to study large-scale phenome variations due to genome variability and interaction with environmental factors.

The xerophytic, but salt-sensitive Sorghum cultivar 'Sweet Sioux' is known as an ion excluder with a high K/Na selectivity at the plasmalemma and tonoplast of epidermal root cells. The aim of this study is the correlation of salt-effected changes in physiological parameters with structural and ultrastructural changes in root cells. The investigation was carried out with root cells because these cells are most directly exposed to the growth medium. Sorghum bicolor xS. sudanensis cv. Sweet Sioux plants were grown under steady-state conditions on nutrient solutions with or without 40 mol m" 3 NaCI. Sorghum sustained this treatment but showed several salt-induced structural and physiological changes which were studied in various cell types of the root tip. (1) NaCI salinity led to a shorter growth region and to salt-induced alterations in the chemical and physical properties of the cell walls in the root tips. (2) Salt treatment also increased the membrane surface in root cells: root cells showed an increase in the quantity of vesicles in the epidermis and in the middle cortex cells. Additionally, some of the epidermis cells of salt-treated plants revealed a characteristic build-up of transfer cells, suggesting an increase in membrane surfaces to increase the uptake and storage of substances. (3) The number of mitochondria increased in the epidermal and in the cortex cells after salt stress thus indicating an additional supply of energy for osmotic adaptation and for selective uptake and transport processes. (4) In the epidermal cytoplasm NaCI stress led to a significant decrease of the P, K, Ca, and S concentrations accompanied by an increase of Na concentration. Electron micrographs show an increase in electron optical contrast within the cytosol and in the matrix of the mitochondria. These results are discussed with regard to the possibility of influence on the part of metabolic functions. (5) The NaCI concentrations were seen to increase and the K concentrations to decrease during salt stress in the vacuoles of the epidermis and cortex cells. The salt-induced increase in vacuolar NaCI concentrations of epidermis and cortex cells are in the region 2 cm behind the root tip, which is sufficient for an osmotic balance towards the growth medium. Additional solutes are necessary 0.5 mm behind the root tip to facilitate osmotic adaptation. The results show ultrastructural changes caused by an Na-avoiding mechanism characterized by a high level of energy consumption. The exclusion of Na from the symplast seems to lead additionally to a decrease in cytoplasmic concentrations of such essential elements as Mg, P, S, and Ca and is thus responsible directly (via energy supply in mitochondria, homeostasis, selectivity of K over Na) or indirectly (via enzyme conformation, cytoplasmic hydration) for the ultrastructural degradation indicated. The salinity-induced multiplicity of structural and functional changes within cell compartments constitutes a group of indicators for the limited NaCI tolerance of Sorghum.

In Mayan culture, the world tree is depicted as a large Kapok or Ceiba tree (Ceiba pentandra), with branches that reach into the sky and touch the heavens (McDonald, 2016). The trunk intersects the earthly forest, while the roots extend deep below ground. Roots reach into the underworld, Xibalba, connecting the physical world to celestial and subterranean spiritual realms. Inside caves of Quintana Roo, Mexico, a physical representation of the world tree can be seen alongside ceremonial altars, sculptures, pots, and tools: tree roots commonly emerge from the ceilings and walls of caves, linking the above-and belowground environments. In contrast to the focus on archaeological studies within these caves, the roots have remained understudied, despite being photographed and noted in journal articles, new stories, and blog posts. Because of this, the importance of the roots is sometimes disregarded, particularly when a cave is commercialized for tourism, during which roots are often cut, potentially harming the associated tree on the surface. This can be particularly problematic for trees that rely on deep water sources within a seasonally dry ecosystem. Seasonally dry and subhumid tropical forests are among the most threatened of the global tropical forests. Quite understudied compared to their wet counterparts, these tropical forests are critical centers of biodiversity and play an important role in global carbon cycling (Poulter et al., 2014; Sánchez-Azofeifa et al., 2005). In order to be successful in ecosystems with seasonal dry periods and high potential evapotranspiration, plants must have physiological adaptations to acquire water or reduce water loss. Deep rooting is an advantageous trait because it can expand a plant's search for water and enable it to reach reliable water at depth (Casper, Schenk, & Jackson, 2003). The occurrence of deep roots is predicted to be more common in dry or subhumid regions, yet, they remain understudied in these types of locations (Schenk & Jackson, 2005). Studying deep roots has obvious limitations because of the inability to access them directly without disturbance (Maeght, Rewald, & Pierret, 2013). Major excavations are costly and generally preclude physiological measurements. However, cave systems that exist close to the surface offer a unique opportunity to study deep roots directly. In addition, when caves are associated with water, this is where tree access to deep water may be expected (Bleby, McElrone, & Jackson, 2010). Although rooting depth in karst environments may be restricted by overlying bedrock, it is not uncommon for trees to grow through preexisting fissures in the bedrock to reach reliable

974 I. Introduction: continuing to face up to root ecology's challenges 975 II. Semantics: defining concepts for better understanding and communication 977 III. Species-level vs ecosystem-level measurements 978 IV. Below-ground plant entities and root classifications 979 V. Contextualisation and reuse of data 988 VI. Experimentation and sampling in laboratory and field 989 VII. Root washing, sorting and storage 1001 VIII. Horizontal plant mobility 1004 IX. Below-ground allocation 1007 X. Root system architecture 1013 XI. Root spatial distribution 1017 XII. Root morphology 1021 XIII. Root anatomy XIV. Root chemistry XV. Root mechanics XVI. Root dynamics XVII. Root respiration and exudation XVIII. Physiology of resource uptake XIX. Mycorrhizal associations XX. Nitrogen-fixing symbioses XXI. Root tip morphology and elongation XXII. Root hair morphology and development XXIII. Root decomposition

Oak (Quercus robur L.) seedlings were grown in pots under controlled conditions and submitted to 34 days of flooding followed by two-week drainage. Roots were significantly affected with reduced extension and dry weight accumulation. After drainage, biomass production of adventitious roots markedly increased in flooded seedlings. Flooding induced a sharp decrease in NO 3-N content in the soil especially in the bottom of pots. NH 4 +-N concentrations increased significantly but at less level compared to NO 3-N decreases. During flooding, root nitrate reductase activity (NRA) was similar to controls while leaf NRA was always below that of controls. The flooded roots maintained amino acid synthesis despite the nitrate depletion in soil. By contrast, leaf amino acid content decreased significantly in flooded seedlings especially at day 34. In flooded seedlings, the transfer of amino acid from cotyledons was disrupted but the transfer capacity was restored after drainage. Relationships between nitrate reduction and changes in soil mineral nitrogen availability are discussed. flooding / mineral nitrogen availability / nitrate reduction / Quercus robur L. Résumé-Influence de l'ennoyage sur la croissance, la biodisponibilité en azote du sol, et sur la réduction des nitrates chez de jeunes semis de chêne pédonculé (Quercus robur L.). Des semis de chêne pédonculé (Quercus robur L.) cultivés en conditions contrôlées ont été soumis à 34 jours d'ennoyage suivi de deux semaines de drainage. La longueur des racines stressées ainsi que leur accumulation de biomasse ont été significativement réduites. Après drainage, la biomasse des racines adventives des semis ennoyés a fortement augmenté. L'ennoyage a induit une forte diminution des teneurs en N-NO 3 dans le sol, particulièrement dans les 5 cm inférieurs du pot. La concentration en N-NH 4 + a augmenté significativement mais sans compenser la diminution de N-NO 3-. Pendant l'ennoyage, les activités nitrate réductase racinaires des deux lots étaient similaires alors que dans les feuilles elle était toujours inférieure chez les plants ennoyés. Les racines ennoyées ont maintenu la synthèse d'acides aminés malgré la disparition des nitrates dans le sol. Au contraire, la teneur en acides aminés dans les feuilles avait significativement diminué dans les semis ennoyés en particulier à 34 jours. Dans les semis ennoyés, le transfert des acides aminés depuis les cotylédons était perturbé, cependant après drainage la capacité de transfert était rétablie. Les relations entre la réduction des nitrates et les changements de la biodisponibilité de l'azote minéral du sol sont discutées. ennoyage / azote minéral disponible / réduction des nitrates / Quercus robur L.

ABSTRACT Cultivated olives are commonly subjected to salinity stress. This is particularly true when orchards are irrigated with saline, recycled, and other marginal waters. Understanding plant response and mechanisms of salt tolerance in olives is imperative to orchard planning and management. Literature concerning olive physiology, growth, and oil production as a function of salinity is reviewed and emphasizes that, in spite of the olive&amp;#39;s general high tolerance for stress, including that caused by salinity, response to salinity and extent of tolerance mechanisms are strongly cultivar-specific. Environmental conditions causing increased root zone salinity can lead to reduced photosynthetic activity, vegetative growth, and fruit and oil production and therefore, salinity is expected to harm production in commercial orchards. Regardless of this, several field studies report that exposure to moderate levels of salinity did not negatively affect yields. Additionally, salinity appears to contribute to positive attributes of olive oil. Proper management of water and salinity, including leaching of salts out of the root zone, can therefore allow optimization of high yields and high oil quality in orchards irrigated with saline water.

Highlights d Tomato cell type-resolution translatome atlas reveals cell type function d Conservation and repurposing in gene regulation between Arabidopsis and tomato d The tomato exodermis is lignified, suberized, and enriched for nitrogen regulation d The root meristem is molecularly homologous across plant species

In Algeria, the region of Mostaganem is known for its agricultural soils with a sandy tendency and abnormally loaded with soluble salts affecting the yields of crops. To assess the salt tolerance threshold of the bean culture Phaseolus vulgaris L. (Fabales Fabaceae) variety “coco rose” was grown in plastic pots filled with two types of substrate, sand and sand amended with 7% bentonite (calcium clay of mining origin). The test was carried out in a greenhouse with controlled climatic conditions (variant temperature between 23-25°C, humidity is around 75% and a photoperiod of 12 hours). At the 5-leaf stage, irrigation with saline was provided with four saline concentrations (0, 50, 100 and 200 meq), the control is irrigated with distilled water. Two weeks later, the microscopic observations were made with an Optica type microscope, the results show a variability of the effect of saline stress depending on the organ and the concentration of the saline treatment. The anatomical structur...

To progress on the understanding of the mechanisms underpinning the coexistence of Mediterranean oak species, we conducted a year-long analysis of the production, architecture and mycorrhization status of the fine roots of a mixed evergreen (Quercus ilex) and winter deciduous (Quercus faginea) oak stand. We used the ingrowth bag technique to sample the fine roots produced by each species in spring, summer and winter. For each season, different root architecture traits (specific root length, root diameter, root tips) and variables associated to root ectomycorrhizal status were measured in the laboratory. Results showed a marked seasonality in the fine-root architecture including more fine-root tips and longer roots per unit of weight formed in spring and summer, revealing a capacity of Mediterranean oak species to modify root architecture in spring and suggesting an increased resource capture in summer. Fine root ectomycorrhizal status was comparable between species, and also showed marked seasonality since we found a high percentage of roots colonized by dead ectomycorrhizas in winter but low ectomycorrhizal colonization rates in summer. Q. ilex produced higher amounts of fine roots than Q. faginea (particularly during spring) suggesting a higher competitive ability of the former species for belowground ressources.

The effects of disturbance by recreational activities (trampling) on changes in soil organic matter (SOM) and on mycorrhizal roots of seedlings and mature trees were studied in four stands of a beech (Fagus sylvatica L.) forest near Basel, Switzerland. At each site, comparable disturbed and undisturbed plots were selected. Disturbance reduced ground cover vegetation and leaf litter. Beech seedlings had lower biomass after disturbance. Ergosterol concentration in seedling roots, an indicator of mycorrhizal fungi, was lower in two of the four disturbed plots compared to undisturbed plots; these two disturbed sites had especially low litter levels. Based on ergosterol measurements, mycorrhizas of mature trees did not appear to be negatively affected by trampling. Total fine roots and SOM were higher in the disturbed than in the undisturbed plots at three sites. At the fourth site, fine roots and SOM in the disturbed areas were lower than in the undisturbed areas most probably due to nutrient input following picnic activities. Principal component analysis revealed a close correlation between SOM and fine roots of mature trees as well as litter and seedling biomass. Trampling due to recreational activities caused considerable damage to the vegetation layer and in particular to the beech seedlings and their mycorrhizal fine roots, whereas, roots of mature trees were apparently resilient to trampling.

A plant phenotyping approach was applied to evaluate growth rate of containerized tree seedlings during the precultivation phase following seed germination. A simple and affordable stereo optical system was used to collect stereoscopic red-green-blue (RGB) images of seedlings at regular intervals of time. Comparative analysis of these images by means of a newly developed software enabled us to calculate (a) the increments of seedlings height and (b) the percentage greenness of seedling leaves. Comparison of these parameters with destructive biomass measurements showed that the height traits can be used to estimate seedling growth for needle-leaved plant species whereas the greenness trait can be used for broad-leaved plant species. Despite the need to adjust for plant type, growth stage and light conditions this new, cheap, rapid, and sustainable phenotyping approach can be used to study large-scale phenome variations due to genome variability and interaction with environmental factors.