Plant Water Relations

Table Olive (Olea europeae L.) is an important crop for the Mediterranean countries. In the past, olive grove were mostly rain fed, due to their resilience to water scarcity; the practice of irrigation is relatively recent and it has been introduced in order to increase crop productions and to improve yield quality (Patumi et al., 2002; D’Andria et al., 2004). Several researches have been focusing on the optimization of irrigation for olive trees (Fernandez and Moreno, 1999) and it has been recognized how, maintaining olive trees under slight or moderate water stress at specific phenological stages, can contribute to optimize yield and water use efficiency (Patumi et al., 1999; Berenguer et al., 2006; Caruso et al., 2011). The impact of water stress, as well as its feasible duration and intensity, depends on crop phenological

Although Jatropha curcas, an important tropical biofuel crop, is reputed for its drought resistance, its ability to perform under dry conditions has hardly been investigated. In a greenhouse experiment we investigated the plant-water relationships of Jatropha seedlings from different accessions under different levels of drought stress. There was little difference in plant water relations between accessions. Drought significantly reduced leaf area, biomass and relative growth rate, but had no effect on specific leaf area, daily range in leaf water potential, leaf water content, transpiration efficiency or aboveground biomass water productivity, corrected for atmospheric conditions. Stem wood density was equally low (0.26 gÂFP -3 ) for all treatments. Stem water content was lowest for dry treatment seedlings. Based on these results, Jatropha could be characterized as a stem succulent tree. In contrast to other stem-succulent deciduous trees, leaves were not shed immediately after the seedlings were confronted with drought. Instead, at the onset of drought, leaves with a higher adaxial stomatal density were formed, after which leaves were only gradually shed. The role of the succulent stem in the water economy of Jatropha was confined to balancing the small water losses of the leaves during drought.

Абстракт. Представят се резултати за коефициента на филтрация Кsat на 9 почвени слоя, получени чрез използване на статистически функции за трансформиране на почвени данни и резултати за Кsat от полеви инфилтрационни тестове за същите разновидности. Отчита се съвпадане и съпоставимост на получените по двата метода стойности, което дава възможност за валидиране на модели на миграцията на арсена на по-голяма територия.

Crop adaptation to waterlogging stress necessitates alterations in their morphophysiological and biochemical characteristics. Cowpeas, which serve as a dualpurpose legume crop (food and fodder), are sensitive to waterlogging stress, especially when exposed to extended periods of water stagnation during the early growth stage. In this study, we subjected five distinct and superior cowpea varieties to 10 days of waterlogging stress at the early seedling stage (V2, 15 days post emergence for 10 days) under controlled conditions. The aim was to comprehend the response of these varieties and identify the ideal trait for screening a large collection of cowpea genetic resources for waterlogging tolerance. We measured and analyzed changes in morpho-physiological and root parameters to gain a deeper understanding of the mechanism underlying waterlogging tolerance. The treatment (waterlogging and control), genotype, and their interactions had a significant impact on the most studied traits (p < 0.05). The results indicated a significant reduction in morpho-physiological parameters such as plant height, leaf area, leaf number, Normalized Difference Vegetation Index (NDVI), chlorophyll content, and chlorophyll fluorescence parameters under stress treatment than control conditions. However, root parameters like the number of adventitious roots (AR) and their length (ARL) significantly increased under waterlogging stress in tolerant cowpea varieties like DC15 and PL4. Correlation and PCA analyses further revealed a positive and significant association between cowpeas' waterlogging tolerance and AR formation and its AR length. Therefore, the current study reveals that swift development of AR and ARL may serve as potential traits conferring waterlogging tolerance in cowpeas. Using suitable mapping populations, these traits could reveal genomic regions associated with waterlogging tolerance in cowpeas. The tolerant varieties and key traits identified in this study could be beneficial in breeding programs aimed at enhancing waterlogging tolerance in cowpeas.

) on morpho-physiological characteristics of banana (Musa sp.) cv., Basrai plants was assessed. Healthy and BBTV infected samples of banana were collected from its open fields and micro-propagated aseptically. These plantlets were established in wire-house for three months. Presence of BBTV was confirmed by polymerase chain reaction (PCR) and enzymelinked immunosorbent assay (ELISA). Micro-propagation efficiency of BBTV-infected plants was observed in less than healthy plants under in-vitro as well as in-vivo. Significant reduction in plant height, fresh weight (F wt) and dry weight (D wt) of leaf was observed in BBTV infected plants. A corelation of peroxidase (POX) activity was observed with total carotenoids that increased in BBTV infected plants, while chlorophyll contents decreased significantly. Nitrate reductase activity also decreased with increase in proline contents in BBTV-stresses plants (p<0.05). Meanwhile, reducing sugars also increased but not-significantly. Bunchy top virus infection in banana therefore resulted in alteration of growth related physiological traits that led to retardation of plant growth.

We investigated the water relations of obli- gate riparian plants on paired diverted and undiverted reaches on Bishop Creek, Eastern Sierra Nevada. Ri- parian plants on diverted reaches had reduced stomatal conductance and water potential compared to plants on undiverted reaches in a dry year, but not in a high runoff year. Juvenile plants on diverted reaches had reduced stomatal conductance and lower midday water potentials relative to surrounding mature trees, a trend that was not observed on undiverted reaches. Plants on diverted reaches possessed significantly smaller, thicker leaves and a reduced total leaf area relative to trees on streamside reaches. Reduced community leaf area and effective stomatal control of water loss may allow ripar- ian corridors on diverted reaches to retain their canopies in low runoff years. However, a long term consequence of partial streamflow diversion may be selective mortal- ty of juvenile plants because of the elimination of floods and high flo...

Western Cape. Sorghum bicolor (L.) Moench is an important cereal crop currently explored as a potential bio-energy crop due to its stress tolerance and ability to ferment soluble sugars. Physiological studies on sorghum varieties have demonstrated that part of drought tolerance is attributed to sugar accumulation in the sorghum stems. Despite the agronomic advantages of sorghum as a bio-energy crop, more research efforts towards the molecular elucidation of sorghum traits that confer drought tolerance are necessary. Particular focus on traits, which could potentially contribute to an efficient bioenergy production under environmental constraints, would be an added advantage. This study examined the role of sugar biosynthesis proteins in conferring tolerance to drought-induced hyperosmotic stress, and ultimately osmotic adjustment in sorghum varieties. Sorghum bicolor (L.) Moench varieties (ICSB338, ICSB73, ICSV213 and S35) with different levels of drought tolerance, were grown under watered conditions until early anthesis after which, a 10-day water deficit period was introduced. iv Control (well-watered) and stressed plants were harvested and used to evaluate plant growth, water retention, chlorophyll content, metabolic profiles, and enzymatic activity of sucrose biosynthesis enzymes. GC-MS based metabolic profiling approach was used to determine the changes in the stem metabolome with stress induction. HPLC analysis was carried out to determine the total soluble sugar content in the stems in all four varieties. Q-PCR was used to determine the levels of mRNA expression of sucrose biosynthesis genes in control and stressed plants. Furthermore, twodimensional gel electrophoresis (2DE) coupled with mass spectrometry was used to identify stress responsive proteins in sorghum plants. A significant reduction in soil water content was observed. As a consequence leaf water content, total chlorophyll content and plant biomass was also reduced. Metabolite analysis revealed a higher abundance of soluble sugars compared to the free amino acid pool, which suggested that osmotic adjustment under stressed conditions was more attributed to sugar content. From a detailed soluble sugar analysis, an increase in total soluble sugars (brix) and hexose concentrations (glucose and fructose) was observed followed by a decrease in sucrose and starch levels in all four sorghum varieties. Gene (mRNA) expression analysis showed an up regulation of sucrose-biosynthesis genes as a consequence of drought stress. However, a direct correlation between the soluble sugar levels and mRNA expression was only evident in ICSV213, indicating that only this variety was responsive to hyperosmotic stress. throughout the course of this study. I am also grateful for the financial support received from the Agricultural Research Council and the Department of Science and Technology.  To Dr Sandile Ndimande, thank you for being a beacon of hope when I was at my lowest point and was ready to throw in the towel. To Dr Omodele Ibraheem, thank you for your guidance, support and friendship throughout this journey. To Dr Ashwil Klein and Dr Hannibal Musarurwa, thank you for your invaluable input during the most challenging period of compiling this document. To Dr Abram Madiehe, thank you for your mentorship.  To the Proteomics Group, thank you for the good and challenging times we have endured together during this learning phase of my life.  To my parents, siblings and extended family, thank you for your encouragement and constant belief in my abilities. My family, Akona and Yakhani Nakani, you've been my true inspiration and motivation in keeping the faith and finishing this race. Thank you. xv Table of Contents KEYWORDS .

Water potential (~b) measurements of Atriplex canescens at the base of the Red Desert near Tipton in Wyoming, revealed a range between -15.5 to -45.1 bars. Minimum values coincided with the lowest air and soil temperatures, maximum with the greatest atmospheric evaporative demand. Change in ~ exceeded 12 bars h -1 during periods of rapidly moving storm systems. Changes in ~ appeared to be independent of plant size, age, sex, and the spatial location of plants. Chemical analyses revealed that xylem sap was up to three times more concentrated at high than at low ~b. It was observed that the flow rate of sap was greater at lower than at higher ~ and that the increase in water movement accounted for the dilution of the baseline concentration of sap solutes. Together, Ca, Mg, K and Na contributed 58% of the mean osmolality of the xylem sap; the dominant ions, however, were K and CI. We suggest that the ability of the species to respond rapidly to changing atmospheric conditions affords it a distinct advantage in a harsh environment.

Grasslands are extensively distributed in flatland areas around the world, such as the Pampas in South America. It is one of the most economically productive landscapes and, as in other regions, they are being replaced by forests at increasing rates. Soil salinization emerges as a negative consequence associated with water deficit and forest groundwater consumption (∼250–500 mm/yr, in this region). An assessment of forest groundwater consumption is crucial for risk evaluation of soil salinization on flatland environments. For this aim, numerical modeling based on physical/biological processes and atmospheric boundary conditions was successfully applied in monitored grassland and afforested plots. Modeling results suggested a partial hydraulic disconnection between forest and phreatic aquifer due to the presence of petrocalcic horizons. Forest transpiration estimates were approximately 13% of total groundwater usage. Forest water consumption was then restricted to that soil portions ...

Low root temperatures significantly reduced root hydraulic conductivity and increased resistance to water flow through the roots of aspen (Populus tremuloides Michx.) seedlings. Increased resistance to water flow could not be fully explained by the corresponding increase in water viscosity at low temperatures. The shapes of Arrhenius plots of root water flow and the activation energies were dependent on the direction, sequence and extent of temperature change. The Arrhenius plots suggested that the effect of low root temperature on root water flow was mediated by an effect on root metabolism. The low root temperatures tested did not induce root electrolyte leakage normally associated with cell membrane injury. Although a decrease in root temperatures to 7 or 4 °C induced a reduction in stomatal conductance, this reduction lagged the decline in root water flow by several hours. In contrast, when soil temperatures were raised from 4 or 7 °C to 25 °C, root water flow presumably increased, and stomatal conductance responded rapidly and was temporarily higher than before the cold treatment was imposed.

Mediterranean evergreen oak woodlands of southern Portugal (montados) are savannah-type ecosystems with a widely sparse tree cover, over extensive grassland. Therefore, ecosystem water fluxes derive from two quite differentiated sources: the trees and the pasture. Partitioning of fluxes according to these different sources is necessary to quantify overall ecosystem water losses as well as to improve knowledge on its functional behaviour. In southern Iberia, these woodlands are subjected to recurrent droughts. Therefore, reaction/resilience to water stress becomes an essential feature of vegetation on these ecosystems. Long-term tree transpiration was recorded for 6 years from a sample of holm oak (Quercus ilex ssp. rotundifolia) trees, using the Granier sap flow method. Ecosystem transpiration was measured by the eddy covariance technique for an 11-month period (February to December 2005), partly coincident with a drought year. Pasture transpiration was estimated as the difference between ecosystem (eddy covariance) and tree (sap flow) transpiration. Pasture transpiration stopped during the summer, when the surface soil dried up. In the other seasons, pasture transpiration showed a strong dependence on rainfall occurrence and on top soil water. Conversely, trees were able to maintain transpiration throughout the summer due to the deep root access to groundwater. Q. ilex trees showed a high resilience to both seasonal and annual drought. Tree transpiration represented more than half of ecosystem transpiration, in spite of the low tree density (30 trees ha À1 ) and crown cover fraction (21%). Tree evapotranspiration was dominated by transpiration (76%), and interception loss represented only 24% of overall tree evaporation.

In other to study the effects of salicylic acid on yield quantity and quality of tomato, an experiment was carried out based on randomized complete blocks design with four replications at research center of Shirvan Agricultural Faculty in 2011. Foliar application of five concentrations of salicylic acid (0, 10 -2 , 10 -4 , 10 -6 , 10 -8 M) were used. Results showed that application of salicylic acid affected tomato yield and quality characters of tomato fruits so that tomato plants treated with salicylic acid 10 -6 M significantly had higher fruit yield (3059.5 g per bush) compared to non-treated plants (2220 g per bush) due to an increase in the number of bunch per bush. Results also indicated that application of salicylic acid significantly improved the fruit quality of tomato. Application of salicylic acid increased the amount of vitamin C, lycopene, diameter of fruit skin and also increased rate of pressure tolerance of fruits. Fruit of tomato plants treated with salicylic acid ...

Regeneration of Pinus jeffreyi in the Sierra Nevada is often limited on sites dominated by Wyethia mollis . Allelopathic chemicals and competition for soil moisture have been suggested as possible mechanisms for limiting regeneration. We tested the hypothesis that soil chemical and microbial properties from sites in different stages of succession influence seedling growth of Pinus jeffreyi . Soil was collected from an early-seral site dominated by Wyethia mollis , a mid-seral site dominated by the shrubs Arctostaphylos patula, Ceanothus prostratus, C. velutinus , and Purshia tridentata , and a late-seral site dominated by mature Pinus . These sites were compared for nutrient content, Pinus seedling growth capacity, and microbial population size. Soil (0-33 cm) from the early-seral site had the lowest C, microbial biomass, and fungal and bacterial populations. There were no consistent trends in soil nutrient content among sites. The early-seral site had the lowest soil Ca and Mg cont...

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A thermodynamic state of solvent and solution separated with an elastic semipermeable membrane, in the box with a fixed volume, is considered. It is shown that the minimum of the free energy is accompanied by the compression of the solution and tension of the solvent caused by the transfer of solvent molecules into compartment with solution. The tensile state of the solvent is described in terms of negative pressure. It is found that the negative pressure as well as compression pressure is of the order of osmotic pressure given by van't Hoff equation. It is proposed that this mechanism could be responsible for the water uptake in tall trees.

A large, truck-mounted screen was constructed to aid in tneasurement of total leaf area of individual honey mesquite (Prosopis gkndulosa Torr.) trees. The screen, which measured 4.6 m X 6.2 m, was constructed with a white tarp supported by a PVC and steel frame, and mounted via steel brackets to one side of P crew-cab truck. To alleviate problems with wind and to facilitate transport, the tarp was attached only at the top of the frame and could be raised and lowered as required. The screen could be transported in the unassembled condition using P standard truck transport frame. The assembled screen was used in P natural rangeland setting to provide P consistent background for photography of individual trees. A 35-mm camera and P portable VCR recorder were used to obtain 2 dimensionnl images of the tree canopy, which were then digitized. These values were related to whole plant leaf area by harvesting entire trees. A crew of 4 was required tu assemble the screen and photograph about 35 trees within 4 hours.

A low-cost, fired-plrce, subcanopy r8.h sbelter WM constructed to f8dlit8tc etudylng wrter rckionr of honey mesquite (Pros& gkhu&losa) growing ln north Texas nngebnd. Thh shelter, combined with 8 supplement81 irri@on system 8nd 8 b8rrier to con-t8ln I8ter8l roots, permitted the study of moisture intluences on tr8nspir8tion, xylem pressure potenthl, 8nd kaf temper8ture on lute wtiy phnts in the field.

Honey mesquite (Prosopisglandulosa Torr.) occurs on a variety of sites varying in soil depth and moisture availability. The objective of this study was to compare water use by honey mesquite on upland, lowland, and riparian sites which were assumed to represent increasing levels of available soil moisture within a single watershed. Effects of the upland and lowland sites were evaluated in 1985. The rlparian site was evaluated with the other 2 sites in 1986. Soil moisture and average daily transpiration were greater (P<O.O5) on the upland than on the lowland site from mid-May to July in both years, and from mid-August through September 1986. These differences were attributed mainly to soil surface characteristics which created greater infiltration on the upland site. The riparian site was near an ephemeral stream and had a water table as shallow as 1.5 m. Soil water content was much greater for this site compared to the other 2 sites throughout 1986. Mesquite transpiration was greater on the riparian site than on the other sites during July 1986, when seasonal vapor pressure deficit was at maximum. However, transpiration was less on the riparian site than on the upland site during May and June 1986. Soil temperature was significantly lower on the riparian than on the upland site and potentially inhibited transpiration on the riparian site in May and June. The study demonstrated a positive relationship between water availability and transpiration by mesquite but did not support the hypothesis that water availability or transpiration was lowest on upland sites.

Cavitation of water columns within the xylem is deleterious for plant water relations as it results in embolism, so reducing hydraulic conductivity. This cavitation can be detected as it is accompanied by the production of acoustic emissions, which can be detected urtrasonically and logged automatically over periods of days. The acoustic emission technique is useful to determine the threshold water potential at which damage to the water-conducting system of the plant is initiated. It can reveal which environmental variables are deleterious to the plant water relations, and which parts of the plant are most sensitive to cavitation. Species comparisons, and comparisons of the same species in different environments can be made, to obtain indications of drought tolerance. However, acoustic emissions have only a limited use in determining the proportion of embolism in a conducting stem, and other methods are needed to find the percentage reduction in hydraulic conductivity.

Hydraulic traits are important for woody plant functioning and distribution. Associations among hydraulic traits, other leaf and stem traits, and species’ performance are relatively well understood for trees, but remain poorly studied for lianas. We evaluated the coordination among hydraulic efficiency (i.e., maximum hydraulic conductivity), hydraulic safety (i.e., cavitation resistance), a suite of eight morphological and physiological traits, and species’ abundances for saplings of 24 liana species and 27 tree species in wet tropical forests in Panama. Trees showed a strong trade‐off between hydraulic efficiency and hydraulic safety, whereas efficiency and safety were decoupled in lianas. Hydraulic efficiency was strongly and similarly correlated with acquisitive traits for lianas and trees (e.g., positively with gas exchange rates and negatively with wood density). Hydraulic safety, however, showed no correlations with other traits in lianas, but with several in trees (e.g., posi...

This experiment was conducted in 2012 - 2013, by using the Factorial experiment on four varieties (Jubilee, Martha, Merit and Sunshine) in 3 repetitions. In the experiment, the effects of the mycorrhiza application on the Plant Height, Stem Diameter, Leaf Nu mber, Flag Leaf Length, Flag Leaf Width, Number of grains per plant, 100 - seed weight and protein percent of the varieties were observed. Accordingly, it was observed that the mycorrhiza application increases the Plant Height, Stem Diameter, Leaf Number, Fl ag Leaf Width, Number of grains per plant, 100 - seed weight and protein percent values for the varieties, while the increase in the Flag Leaf Height was deemed to be statistically insignificant. It is believed that the mycorrhiza application will be benefic ial from the perspective of enhancing plant development both in natural and agricultural ecosystems.

Three independent methods were used to evaluate transpiration of a boreal forest: the branch bag, sap flow and eddy covariance methods. The branch bag method encloses several thousand needles and gives a continuous record of branch transpiration. The sap flow method provides a continuous record of sap velocity and an estimate of tree transpiration. The eddy covariance method typically measures evaporation rates between a forest and the atmosphere. We deployed an extra eddy covariance system below the forest to estimate canopy transpiration by difference. The three systems detected small water vapor fluxes despite a plentiful supply of energy to drive evaporation. We also observed that transpiration rates were low even when the soil was well supplied with water. Low rates of transpiration were attributed to the canopy's low leaf area index and the marked reduction in stomatal conductance as vapor pressure deficits increased. Water vapor fluxes, derived from the sap flow method, lagged behind those derived by the branch bag method by 1 to 2 h. The sap flow method also suffered from sampling errors caused by the non-uniformity of flow across the sapwood and the spatial variability of sapwood cross section throughout the forest. Despite technical difficulties associated with hourly measurements, daily totals of transpiration agreed well with values derived from micrometeorological systems.

El objetivo de este estudio es evaluar el crecimiento inicial de la caña de azúcar variedad RB 86-7515, cultivada en sistema de producción orgánica y fertilizada con dosis de lithothanmium y vinaza, se desarrolló un experimento. La investigación se llevó a cabo en la Escuela de Agronomía de la Universidade Federal de Goiás, Brasil. El delineamiento estadístico fue en un diseño completamente aleatorio con tres repeticiones, en esquema factorial (5 x 5 x 2). Las plantas fueron cultivadas en contenedores de plástico de 200 litros. Los tratamientos correspondieron a cinco dosis de vinaza (0, 165, 330, 495 e 660 m3.h-1) y cinco dosis de lithothanmium (0, 100, 200, 300 e 400 kg.ha-1) en dos ambientes: irrigado y no irrigado. El sistema de irrigación utilizado fue por goteo con emisores de 4 L.h-1. La aplicación de los tratamientos de fertilización, fueron divididas de acuerdo con la marcha de absorción de nutrientes por las plantas de caña de azúcar. Se evaluaron número de brotes (cañas),...

Contents Summary I. Introduction II. Comparison of various definitions and measurement techniques of minimum conductance III. Cuticular conductance IV. Contribution of stomata V. Environmental and ecological variation in minimum conductance VI. Use of minimum conductance in models VII. Conclusions Acknowledgements References SUMMARY: When the rate of photosynthesis is greatly diminished, such as during severe drought, extreme temperature or low light, it seems advantageous for plants to close stomata and completely halt water loss. However, water loss continues through the cuticle and incompletely closed stomata, together constituting the leaf minimum conductance (g ). In this review, we critically evaluate the sources of variation in g , quantitatively compare various methods for its estimation, and illustrate the role of g in models of leaf gas exchange. A literature compilation of g as measured by the weight loss of detached leaves is presented, which shows much variation in this...

Supplemental irrigation under prolonged drought conditions has a key role in providing water for transpiration of rain-fed fig trees. The effect of different times and amounts of supplemental irrigation at different distances from the tree trunk on quantity and quality of Estahban rain-fed fig production was evaluated during two years. A randomized complete block design with four replications on fig cultivars of Sabz was used to conduct the experiment. Treatments of supplemental irrigation included three different application positions including: close to tree trunks (NT); 1-1.1 m from tree trunk (UT) and outside of tree canopy (OT), using three different quantities of irrigation water as no supplemental irrigation (control), 1000 and 2000 liters irrigation water per tree, and with two different supplemental irrigation times in early spring and mid-summer. Results showed higher soil water content for irrigation during early spring, near tree trunk with 2000 liters irrigation water p...

Climate change is a major environmental challenge worldwide. Over the past century, human activities have dramatically altered the Earth's atmospheric composition, with significant consequences for the planet's climate, biogeochemistry, ecosystems and societies. Plant diseases are already causing extensive crop losses throughout the world and these extreme weather conditions along with warmer temperature will aggravate these impacts. Change in climate also affect disease management with regard to timing, preference, and efficacy of chemical, physical, and biological measures of control and their utilization within integrated pest management strategies. Climate change is just one of the many ways in which the environment can move in the long term from disease-suppressive to disease-conducive or vice versa. Therefore, plant diseases could be even used as indicators of climate change. Climate change is indeed not only going to threaten plant health, but may in some cases enhance it estimating disease risk on a large scale is necessary for identifying research priorities, strategically orienting industry, and developing public policies for establishing measures of adaptation that will allow the maintenance of food security. A limited amount of information on the potential impacts of climate change on plant diseases is available. This overview addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health.

In the latest years, scarcity of rainfall in North Kordofan of Sudan led to the search for irrigation water for cultivation of fodder crops to fill the gap in fodder production, hence the North Kordofan state characterized by a limited water situations. Therefore, efficient use of irrigation water seems to be of vital importance. This situation emphasizes the need for using earlier variety and scientifically sound methods for deciding when and how much to irrigate the crops. A field experiment was carried out during two successive seasons (2014/2015) and (2015/2016), to investigate the effect of ten genotypes and two watering intervals (seven and ten days) on growth and yield of forage sorghum. The treatments were arrange in a split plot design with three replications. The results showed that there were significant differences among watering intervals and genotypes for the most characters measured. The Watering interval of seven days significantly improved growth and forage yield of...

Grasslands are extensively distributed in flatland areas around the world, such as the Pampas in South America. It is one of the most economically productive landscapes and, as in other regions, they are being replaced by forests at increasing rates. Soil salinization emerges as a negative consequence associated with water deficit and forest groundwater consumption (∼250–500 mm/yr, in this region). An assessment of forest groundwater consumption is crucial for risk evaluation of soil salinization on flatland environments. For this aim, numerical modeling based on physical/biological processes and atmospheric boundary conditions was successfully applied in monitored grassland and afforested plots. Modeling results suggested a partial hydraulic disconnection between forest and phreatic aquifer due to the presence of petrocalcic horizons. Forest transpiration estimates were approximately 13% of total groundwater usage. Forest water consumption was then restricted to that soil portions ...

La energía y el agua en un ecosistema están íntimamente ligadas, ya que la radiación total es básica para el desarrollo de la evapotranspiración, que, a su vez, es un componente importante en el flujo de agua y de energía de un bosque, de una comunidad vegetal. La radiación total es el equilibrio entre la radiación entrante y saliente de onda corta y larga. Los ecosistemas afectan a la radiación total a través de albedo (reflexión de onda corta), que depende de la reflexión de hojas individuales y de otras superficies junto con la rugosidad del vuelo, la cual está afectada por su altura y complejidad. Gran parte de la energía absorbida es liberada a la atmósfera como flujo de calor latente (evapotranspiración) y como flujo de calor sensible. El primero enfría la superficie y transfiere vapor de agua a la atmósfera, mientras que el segundo calienta el aire de superficie. El coeficiente de Bowen, el cociente entre el flujo de calor sensible y el latente, determina la relación entre el ciclo del agua y el de la energía. El agua penetra en el ecosistema terrestre, principalmente, a través de la precipitación y lo abandona por evapotranspiración, escorrentía e infiltración. El agua circula por los ecosistemas como respuesta a los gradientes de potencial de agua, que vienen determinados por el potencial de presión, el potencial osmótico, el potencial gravitacional y el potencial matricial. El agua disponible en el suelo se desplaza hacia la atmósfera a través de la planta por el continuo hídrico suelo-planta-atmósfera, el cual está generado por el gradiente de potencial hídrico. Este flujo se produce tanto en la fase líquida como en la de vapor y viene condicionado por fenómenos internos, propios de la planta, de la comunidad (especie, edad, estado fisiológico, patologías,.....) y externos, los denominados estreses ambientales, tanto bióticos (patologías, herbivoría, competencia intra/inter específica,...) como abióticos (altas y bajas temperaturas, sequía, salinidad, radiación, contaminación, fuego,...).

Atmospheric CO 2 concentration (C a ) continues to rise. An imperative exists, therefore, to elucidate the interactive effects of elevated C a and drought on plant water relations of wheat (Triticum aestivum L.). A spring wheat (cv. Yecora Rojo) crop was exposed to ambient (Control: 370 mmol mol 21 ) and free-air CO 2 enrichment (FACE: ambient 1 180 mmol mol 21 ) under ample (Wet), and reduced (Dry), water supplies (100 and 50% replacement of evapotranspiration, respectively) over a 2-yr study. Our objective was to characterize and quantify the responses of 26 edaphic, gas exchange, water relations, carbohydrate pool dynamics, growth, and development parameters to rising C a and drought. Increasing C a minimized the deleterious effects of soil-water depletion by increasing drought avoidance (i.e., lower stomatal conductance and transpiration rate, and growth and development of a more robust root system) and drought tolerance (i.e., enhanced osmoregulation and adaptation of tissue) mechanisms, resulting in a 30% reduction in water stress-induced midafternoon depressions in net assimilation rate. An elevated C a -based increase in daily and seasonal carbon gain resulted in a positive feedback between source capacity (shoots) and sink demand (roots). Devoid of a concomitant rise in global temperature resulting from the rise in C a , improved water relations for a herbaceous, cool-season, annual, C 3 cereal monocot grass (i.e., wheat) are anticipated in a future high-CO 2 world. These findings are applicable to other graminaceous species of a similar function-type as wheat common to temperate zone grassland prairies and savannas, especially under dryland conditions. T HE atmospheric CO 2 concentration (C a ) is rising about 0.5% per annum from present day levels of approximately 370 mmol mol 21 and is projected to reach 500 to 1000 mmol mol 21 by the 21st century, depending on future emission rates (IPCC, 1996. The increase in C a , as well as of other radiatively active gases, is predicted to cause global warming and to alter precipitation patterns . Higher levels of C a directly affects the physiology, water re-lations, growth, and development of plants , as do warmer temperatures and altered water supplies. In this article we focus on the effects of elevated C a on the water relations of wheat at both ample and stress levels of soilwater supply.

Conocarpus lancifolius is an ornamental plant that flourishes under the semi-arid conditions of Kuwait. The adaptive response of this species to drought, salinity stress and the relationship of free polyamines in leaves, leaf osmotic potential, chlorophyll content and fluorescence were determined. These were done with single shoots (14-15 leaves) in a controlled environmental chamber at 25°C and RH of 45-50%. The leaves of plants treated with 1.37 M NaCl had a relative water content (RWC) of 65% or lower. Shoot elongation and leaf development ceased just after leaf osmotic potential (ȥ s) of 3.32 MPa and the threshold for salt damage in the leaves appeared to be at 1.03-1.37 M NaCl after 10 days. The level of salt tolerance indicated that C. lancifolius may be a xerohalophyte. The chlorophyll (chl) content index increased by the formation of green islands and declined with ultrastructural changes of the chloroplasts in 1.37-1.71 M NaCl. The minimal Chl fluorescence (Fo) increased with increase in salinity and drought but the electron transport rate ETR, photochemical quantum yield (Y), photochemical quenching (qP) and variable to maximal fluorescence (Fv/Fm) declined after 10 and 4 DAT with increase in salinity and drought, respectively, an indication of some damage to PSII. Putrescine (Put) was the predominant polyamine during the early stages of drought and salinity stress. Although Put was the most abundant polyamine in 0.17-0.34 M NaCl, at higher concentrations spermidine (Spd) and spermine (Spm) were more abundant. The titer and type of polyamine accumulated in C. lancifolius appeared to be related to the nature, intensity and duration of environmental stress. Understanding its response to drought and salinity stress will assist in the management and longevity of this species.

Soil water is an important resource that imposes limitations on optimal plant performance in semiarid regions. In some of these regions, shrubs form a characteristic component of farmers' fields and potentially impact crop productivity. Consequently, a 2-year study on soil water dynamics and shrub rooting patterns was conducted during the dry season and transition into the wet season with fields having Pearl millet intercropped with shrubs. Millet roots predominantly exploited the 0.2-0.5 m depth range with 95% of shrub roots in the upper 0.5 m. Soil volumetric water content (soil water content) decreased with greater radial distance from shrubs up to 2 m but progressively increased with soil depth. During the dry season, soil surrounding shrub roots was consistently moister than adjacent bare soil albeit at depth, soil moisture content declined steadly in the 0.9-1.2 m depth range due to depletion by shrub roots. On the contrary, the 0.2 and 0.4 m zones depicted slight increments in soil moisture which could be attributed to soil water redistribution by shrub roots. During the rainy season, shrub presence had a considerable impact on the fate of the field soil moisture regime with shrub roots serving as pathways for deep profile recharge. Shrubs exploited the deeper profile (0.9-1.2 m) as opposed to the Pearl millet (0.2-0.5 m) suggesting that intercropping of annual crops with shrub stands could serve as an innovative and viable agronomic option in these vulnerable Sahel agro-ecosystmes.

Background Tropical montane cloud forests (TMCFs) are characterized by a unique set of biological and hydroclimatic features, including frequent and/or persistent fog, cool temperatures, and high biodiversity and endemism. These forests are one of the most vulnerable ecosystems to climate change given their small geographic range, high endemism and dependence on a rare microclimatic envelope. The frequency of atmospheric water deficits for some TMCFs is likely to increase in the future, but the consequences for the integrity and distribution of these ecosystems are uncertain. In order to investigate plant and ecosystem responses to climate change, we need to know how TMCF species function in response to current climate, which factors shape function and ecology most and how these will change into the future. † Scope This review focuses on recent advances in ecophysiological research of TMCF plants to establish a link between TMCF hydrometeorological conditions and vegetation distribution, functioning and survival. The hydraulic characteristics of TMCF trees are discussed, together with the prevalence and ecological consequences of foliar uptake of fog water (FWU) in TMCFs, a key process that allows efficient acquisition of water during cloud immersion periods, minimizing water deficits and favouring survival of species prone to drought-induced hydraulic failure. † Conclusions Fog occurrence is the single most important microclimatic feature affecting the distribution and function of TMCF plants. Plants in TMCFs are very vulnerable to drought (possessing a small hydraulic safety margin), and the presence of fog and FWU minimizes the occurrence of tree water deficits and thus favours the survival of TMCF trees where such deficits may occur. Characterizing the interplay between microclimatic dynamics and plant water relations is key to foster more realistic projections about climate change effects on TMCF functioning and distribution.

Aims: Direct methods of measuring saturated hydraulic conductivity (K s), either in situ or in the laboratory, are time consuming and very expensive. Several Pedotransfer functions (PTFs) are available for estimating K s , with each having its own limitations. In this study, the performances of four popular PTFs were evaluated on different soil classes in the semi deciduous zone of Ghana. The PTFs considered herein were Puckett et al. (1985), Campbell and Shiozawa (1994), Dane and Puckett (1994), and Ferrer-Julià et al. (2004). In addition, five local data derived PTFs were used to study the possibility of using local datasets to validate PTF accuracy. Materials and Methods: A total of 450 undisturbed soil cores were collected from the 0-15 cm depth from three benchmark soils, namely, Stagni-Dystric Gleysol (SDG), Plinthi Ferric Acrisol (PFA) and Plinthic Acrisol (PA). The K s of samples were measured by the falling-head permeameter method in the laboratory. Sand, silt and clay fractions, bulk density, organic matter content, and exchangeable calcium and sodium were measured and used as input parameters for the newly derived PTFs. Accuracy and reliability of the predictions were evaluated by the root mean square error (RMSE), coefficient of correlation (r), index of agreement (d), and the Nash-Sutcliffe efficiency (NSE) between the measured and predicted values from both tested and newly derived PTFs. The relative improvement (RI) of the newly derived PTFs from this study over the existing ones were also evaluated. Results: The newly derived PTFs in this study had higher prediction accuracy with r, d, RMSE and NSE ranging from 0.80-0.99, 0.79-0.94, 0.14-1.74 and 0.84-0.98, respectively, compared with 0.32-0.45, 0.27-0.50, 4.00-4.90 and 0.41-0.47 for the tested PTFs. The relative improvement of the newly derived over the tested PTFs ranged from 56.50-95.71% in the SDG, 70.73-96.89% in the PFA, and 65.37-95.81% in the PA. Generally, RI was observed to be highest for Model 1 in the SDG, and Model 4 in both PFA and PA, and lowest for Model 5 in all three soils. It was observed that the inclusion of exchangeable calcium and sodium as predictors increased the predictability of the newly derived PTFs.

Investigating the 2D-T 2-T 2-relaxation exchange of interstitial water in a packing of sedimented Stöber-silicate spheres, we come the conclusion that contrary to its behaviour in macro-pores, water confined in nano-pores of silica exhibits enhanced diffusivity. The 2D-experiments, performed at different temperatures, reveal a temperature-dependent bimodal relaxation distribution and two-site relaxation exchange. Our recently introduced kinetic multi-site exchange model is applied to derive the according exchange rates. The resulting Arrhenius plot produces an exchange activation energy of 7 kJ/mol, which is well below the hydrogen bond energy or the activation energy for self-diffusion of water in the bulk. A possible hopping-mechanism as the source of enhanced proton-diffusion in nanoporous silica is discussed, as well as its significance to mass transfer in porous media.

We present the results of a 5-year examination of variation in the stable carbon isotope composition (~) of three C 3 graminoid species from a Sandhills prairie: Agropyron smithii, Carex heliophila and Stipa comata. Although consistent species-specifc patterns for mean were seen, there was also significant and substantial among-year and within-season variation in & A smaller contribution to variation in ~ came from topographic variation among sampling sites. Effects of species, year, season and topography contribute to variation in ~ in an additive manner. An association between climate and ~ exists that is consistent with previous work suggesting that ~ reflects the interplay between photosynthetic gas exchange and plant water relations. Within the growing season, the time over which 5 integrates plant response to the environment ranges from days to months.

Worldwide rice productivity is being threatened by increased endeavours of drought stress. Among the visible symptoms of drought stress, hampered water relations and disrupted cellular membrane functions are the most important. Exogenous use of polyamines (PAs), salicylic acid (SA), brassinosteroids (BRs), glycinebetaine (GB) and nitrous oxide (NO) can induce abiotic stresses tolerance in many crops. In this time course study, we appraised the comparative role of all these substances to improve the drought tolerance in rice (Oryza sativa L.) cultivar Super‐Basmati. Plants were subjected to drought stress at four leaf stage (4 weeks after emergence) by maintaining soil moisture at 50 % of field capacity. Pre‐optimized concentrations of GB (150 mg l−1), SA (100 mg l−1), NO (100 μmol l−1 sodium nitroprusside as NO donor), BR (0.01 μm 24‐epibrassinolide) and spermine (Spm; 10 μm) were foliar sprayed at five‐leaf stage (5 weeks after emergence). There were two controls both receiving no ...

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Worldwide rice productivity is being threatened by increased endeavours of drought stress. Among the visible symptoms of drought stress, hampered water relations and disrupted cellular membrane functions are the most important. Exogenous use of polyamines (PAs), salicylic acid (SA), brassinosteroids (BRs), glycinebetaine (GB) and nitrous oxide (NO) can induce abiotic stresses tolerance in many crops. In this time course study, we appraised the comparative role of all these substances to improve the drought tolerance in rice (Oryza sativa L.) cultivar Super‐Basmati. Plants were subjected to drought stress at four leaf stage (4 weeks after emergence) by maintaining soil moisture at 50 % of field capacity. Pre‐optimized concentrations of GB (150 mg l−1), SA (100 mg l−1), NO (100 μmol l−1 sodium nitroprusside as NO donor), BR (0.01 μm 24‐epibrassinolide) and spermine (Spm; 10 μm) were foliar sprayed at five‐leaf stage (5 weeks after emergence). There were two controls both receiving no ...

A pot experiment was conducted to study the effects of water deficit on vegetative and reproductive stages of Hybrid, Open pollinated (OPV) and Local varieties of maize. Water deficit at vegetative stage significantly reduced plant height, leaf area, shoot dry matter, root dry matter of the upper 25 cm depth, kernel number and grain yield per plant as compared to well watered plant. Water deficit at reproductive stage reduced more leaf area, kernel number and grain yield per plant than water deficit at vegetative stage. Water deficit at reproductive stage also reduced shoot dry matter, kernel size and harvest index. Leaf water potential and relative water content taken at 58 and 60 days after planting were also reduced by water deficit. The Local variety was taller with smaller kernel size and lower harvest index than Open pollinated and Hybrid varieties. There were no significant interactions among the varieties and water deficit treatments. Key words: Leaf water potential, relativ...

Northeastern U.S. coastal grasslands are biologically, culturally, and historically significant but are being lost through the invasion of woody plants, including native species Gaylussacia baccata Wangenh. and Smilax rotundifolia L. Soil changes induced by these woody plants have important implications for herbaceous species diversity and restoration potential. We determined the effects of young and old G. baccata and S. rotundifolia patches on soil properties and plant diversity and identified relationships among soil properties and plant diversity. On a coastal grassland on Naushon Island (MA, USA) in 2015 and 2016, we used a time sequence of satellite imagery to identify young (< 5 years) and old (> 20 years) patches of G. baccata and S. rotundifolia. In these areas and in remaining grassland patches, we sampled soil properties, leaf 15 N, and herbaceous plant diversity. All soils had low pH and higher extractable NH 4 + than NO 3 −. G. baccata had relatively low extractable soil NO 3 − , soil potential nitrification, and leaf δ 15 N, while S. rotundifolia had relatively high extractable soil NH 4 + , low soil pH, and high leaf %N. Herbaceous plant diversity was low under S. rotundifolia and nearly absent under G. baccata, and most effects were more pronounced in older woody plant patches. Species diversity correlated with different soil variables between the two woody plants, indicating different mechanisms may drive diversity loss. Especially in older woody plant patches, restoration efforts should take into account soil changes, such as by making use of soil amendments. This could help offset soil effects after woody plant clearance and better enable grassland species recovery. Keywords Coastal ecosystems. Native plant invasions. Land restoration. N cycling. Northeastern U.S.

Salicylic acid (SA), an endogenous plant growth regulator has been found to generate a wide range of metabolic and physiological responses in plants thereby affecting their growth and development. In the present review, we have focused on various intrinsic biosynthetic pathways, interplay of SA and MeSA, its long distance transport and signaling. The effect of exogenous application of SA on bio-productivity, growth, photosynthesis, plant water relations, various enzyme activities and its effect on the plants exposed to various biotic and abiotic stresses has also been discussed.

Seedlings from four provenances of Jatropha curcas were subjected to 80, 50, and 30% of soil field capacity in potted experiments in order to study their responses to water availability. Our results showed that with the decline of soil water availability, plant growth, biomass accumulation, net photosynthetic rate, stomatal conductance (g s), and transpiration rate (E) decreased, whereas leaf carbon isotope composition (δ 13 C), leaf pigment contents, and stomatal limitation value increased, while maximal quantum yield of PSII photochemistry was not affected. Our findings proved that stomatal limitation to photosynthesis dominated in J. curcas under low water availability. The increase of δ 13 C should be attributed to the decrease in g s and E under the lowest water supply. J. curcas could adapt to low water availability by adjusting its plant size, stomata closure, reduction of E, increasing δ 13 C, and leaf pigment contents. Moreover, effects of provenance and the interaction with the watering regime were detected in growth and many physiological parameters. The provenance from xeric habitats showed stronger plasticity in the plant size than that from other provenances under drought. The variations may be used as criteria for variety/provenance selection and improvement of J. curcas performance.