Soil CO 2 efflux is the main source of CO 2 from forest ecosystems and it is tightly coupled to t... more Soil CO 2 efflux is the main source of CO 2 from forest ecosystems and it is tightly coupled to the transfer of recent photosynthetic assimilates belowground and their metabolism in roots, mycorrhiza and rhizosphere microorganisms feeding on rootderived exudates. The objectives of our study were to assess patterns of belowground carbon allocation among tree species and along seasons. Pure 13 CO 2 pulse labelling of the entire crown of three different tree species (beech, oak and pine) was carried out at distinct phenological stages. Excess 13 C in soil CO 2 efflux was tracked using tunable diode laser absorption spectrometry to determine time lags between the start of the labelling and the appearance of 13 C in soil CO 2 efflux and the amount of 13 C allocated to soil CO 2 efflux. Isotope composition (δ 13 C) of CO 2 respired by fine roots and soil microbes was measured at several occasions after labelling, together with δ 13 C of bulk root tissue and microbial carbon. Time lags ranged from 0.5 to 1.3 days in beech and oak and were longer in pine (1.6-2.7 days during the active growing season, more than 4 days during the resting season), and the transfer of C to the microbial biomass was as fast as to the fine roots. The amount of 13 C allocated to soil CO 2 efflux was estimated from a compartment model. Seasonal patterns of carbon allocation to soil CO 2 efflux differed markedly between species, with pronounced seasonal variations in pine and beech. In beech, it may reflect competition with other sinks (aboveground growth in late spring and storage in late summer) that were not observed in oak.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 19, 2022
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Plant material enriched in stable isotopes such as 13C and 15N can provide detailed insights into... more Plant material enriched in stable isotopes such as 13C and 15N can provide detailed insights into the fate of carbon and nitrogen during litter decomposition on land and in water. Large amounts (>1 kg) of labelled material are often needed for partitioning isotopic tracers in food webs and quantifying elemental fluxes at the ecosystem scale. This chapter describes two procedures, leaf spraying and stem injection, to produce leaf litter homogenously labelled and highly enriched in 15N. Leaf spraying uses 15N-labelled urea applied as a mist to fully expanded and physiologically active leaves or to the whole tree canopy. The labelled urea is rapidly taken up by the leaves. The stem injection technique involves connecting a reservoir containing 15N-labelling solution (15N labelled NH4NO3) to a borehole in the stem extending to the xylem. The upward sap flow induced by transpiration carries the label to the leaves. The labelled leaves are harvested following natural senescence just before or after abscission. These techniques have proved useful for tracing the fate of litter N in forest soils and would also be valuable for analyzing N fluxes associated with decomposing litter in streams.
For forest ecosystems, the relationship between root biomass, root growth and soil nitrification ... more For forest ecosystems, the relationship between root biomass, root growth and soil nitrification is still debated. Following repeated findings of significant differences in soil nitrification beneath comparable stands at the Breuil experimental site, a reciprocal soil exchange experiment combining high (H)-and low (L)-nitrifying stands was conducted to highlight the effect of tree root colonization on the control of nitrification. Soil percent nitrification and fine root biomass were measured in undisturbed and in transplanted soil cores after 16 and 28 months. In undisturbed soils, the fine root biomass varied by tree species and explained only 14% of the variation in percent nitrification. In transplanted soil cores, percent nitrification converged, at different rates, towards values close to those measured in the undisturbed soil at the receptor stands. On the one hand, percent nitrification increased rapidly in soil cores from L transferred to H, while soil core colonization by roots remained low during the study period. Soil cores might have been colonized by active nitrifiers from their new environment, or/and the activity of the nitrifiers originally present was less suppressed by root activity in their new environment. On the other hand, percent nitrification decreased progressively in soil cores from H transferred to L as root colonization increased. This suggests that root colonization reduced nitrifier population and activity. Our findings suggest that the often-reported influence of forest species on soil nitrification is probably multifactorial but the tree root colonization contributes.
Data from: Convergence of soil nitrogen isotopes across global climate gradients
Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future p... more Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems, and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the 15N:14N ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling. In synthesizing data from over 6000 soil samples, we show strong global relationships among soil N isotopes, mean annual temperature (MAT), mean annual precipitation (MAP), and the concentrations of organic carbon and clay in soil. In both hot ecosystems and dry ecosystems, soil organic matter was more enriched in 15N than in corresponding cold ecosystems or wet ecosystems. Below a MAT of 9.8°C, soil δ15N was invariant with MAT. At the global scale, soil organic C concentrations also declined with increasing MAT and decreasing MAP. After standardizing for variation among mineral soils in soil C and clay concentrations, soil δ15N showed no consistent trends across global climate and latitudinal gradients. Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss
Coffee production, nitrate leaching and N2O emission in Coffea arabica systems in Costa Rica according to fertilization and shade management
In Costa Rica, heavily fertilized Coffea arabica plantations grown on permeable soils under high ... more In Costa Rica, heavily fertilized Coffea arabica plantations grown on permeable soils under high rainfalls are one of the suspected causes of nitrate (NO3) pollution of groundwater and nitrous oxide (N2O) emissions to the atmosphere (Babbar and Zak, 1995). The inclusion of trees in coffee plantations may limit nutrient leaching by increasing nutrient uptake but may also reduce coffee production as a result of competition for light, water and soil nutrients. Whereas many coffee agroforestry systems (AFS) in Costa Rica are still conventionally managed (using high mineral N fertilization rates), alternative technologies using organic fertilizers and leguminous shade trees are extending. This study presents some results on the effects of N fertilization and shade management on coffee production, permanent biomass accumulation, NO3- leaching and N2O emissions, in contrasting Costa Rican coffee systems.
Understanding how climate and soil hydrology control tree growth is critical to predict the respo... more Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in southwestern Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall. We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.
Background: Increased exportation of harvest residues from forests, to mitigate excessive demand ... more Background: Increased exportation of harvest residues from forests, to mitigate excessive demand for woody biomass, have reportedly diminished soil mineral resources and may lead to degraded tree nutrition and tree growth. However, as nutrients become less available in the soil, the remobilization of nutrients in biomass tissues (plant internal cycling) helps sustain tree nutrition. Our study aims to quantify the impact of Removing Harvest Residues and Litter (RHRL) during five years on tree growth, wood density and stem wood nutrient concentrations in young beech and oak forest stands.Result: Our study found that, RHRL significantly decreased the tree growth ring width, by 14%, and wood density, by 3%, in beech trees, in the near bark rings. RHRL also significantly reduced the nutrient concentration in the near bark and near pith area of both species. Mg, Na and S were found lower by 44%, 76% and 56%, respectively, in the near bark area of beech trees, and K, Ca, Mg, Na, S and Fe w...
Background: Intensive silvicultural practices and the planting of monospecific forests of conifer... more Background: Intensive silvicultural practices and the planting of monospecific forests of coniferous, more productive compared to hardwoods, may threaten over the mid to long-term the sustainability of soil chemical fertility of forest ecosystems and is a major concern for forest managers and policy.Methods: We investigated the tree species effect (Quercus sessiliflora Smith, Fagus sylvatica L., Picea abies Karst., Pseudotsuga menziesii Mirb. Franco., Abies nordmanniana Spach. and Pinus nigra Arn. ssp laricio Poiret var corsicana) on the change over time of soil chemical properties and nutrient pool sizes in the mineral and organic layers of the soil during the 45 years after the plantation of the Breuil-Chenue common garden experiment (Burgundy, France). The organic and mineral soil layers down to 70 cm depth were sampled in the different monospecific plots in 1974, 2001 and 2019. Results: The Ca and Mg exchangeable pools and soil pH increased over the entire soil profile in most s...
Understanding how climate and soil hydrology control tree growth is critical to predict the respo... more Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in southwestern Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall. We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.
Originality significance statement: This is the first study demonstrating biological nitrificatio... more Originality significance statement: This is the first study demonstrating biological nitrification inhibition (BNI) by tree species which directly affects the abundance of soil Nitrobacter. Before this work, BNI was thought to mostly affect ammonia oxidizers. This is an important breakthrough for understanding plant-microorganisms interaction processes that underlie niche construction by plants growing in environments with low soil N availability. Summary Some temperate tree species are associated with very low soil nitrification rates, with important implications for forest N dynamics, presumably due to their potential for biological nitrification inhibition (BNI). However, evidence for BNI in forest ecosystems is scarce so far and the nitrifier groups controlled by BNI-tree species have not been identified. Here we evaluated how some tree species can control soil nitrification by providing direct evidence of BNI and identifying the nitrifier group(s) affected. First, by comparing 28 year-old monocultures of several tree species, we showed that nitrification rates correlated strongly with the abundance of nitrite oxidizers Nitrobacter (50-to 1000-fold changes between tree monocultures) and only weakly with the abundance of ammonia oxidizing archaea (AOA). Second, using reciprocal transplantation of soil cores between low and high nitrification stands, we demonstrated that nitrification changed 16 months after transplantation and was correlated to changes in the abundance of Nitrobacter, not AOA Third, extracts of litter or soil collected from the low nitrification stands of Picea abies and Abies nordmanniana inhibited the growth of Nitrobacter hamburgensis X14. Our results provide for the first time direct evidence of BNI by tree species directly affecting the abundance of Nitrobacter.
Nitrogen (N) made available through the decomposition of organic matter is a major source for pla... more Nitrogen (N) made available through the decomposition of organic matter is a major source for plants in terrestrial ecosystems. N cycling in Siberia is however poorly documented despite the region representing a substantial surface area of the globe. We studied the influence of pedo-climate (using two forest-steppe and two southern taiga sites) and vegetation type (aspen forest and grassland) on the redistribution of N released from decomposing 15 N-labelled leaf-litter in southwestern (SW) Siberia. A model of N dynamics was fit to field measurements that yielded estimates of N mean residence time (MRT) within litter and soil layers, as well as the proportion of N transferred from one layer to another. The release of N from the aspen litter was slower in the forest-steppe (MRT in litter: 2.9-4.6 years) than in the southern taiga (0.9-1.5 years), likely because winter soil freezing and summer drought slowed decomposition in the forest-steppe. In contrast, no difference between the bioclimatic zones was observed for the grass litter (MRT 1.2-1.6 years), suggesting litter chemistry outweighs pedo-climate in these zones. While most of the vertical transfer of N down the soil profile occurred during the vegetative season, important losses were observed after snow-melt. Over three years, the transfer of N within the soil profile was deeper in the southern taiga sites than in the forest-steppe,
Climate change is particularly strong in Northern Eurasia and substantial ecological changes are ... more Climate change is particularly strong in Northern Eurasia and substantial ecological changes are expected in this wide region. The reshaping and the migration northward of bioclimatic zones may offer opportunities for agriculture development in western and central Siberia. However, the bioclimatic vegetation models currently employed for projections still do not consider soil fertility whereas it is highly critical for plant growth. In the present study, we surveyed the phosphorus (P) status in the south-west of Siberia where soils are developed on loess parent material. We selected six sites differing by pedoclimate conditions and sampled the soil at different depths down to one meter in aspen (<i>Populus tremula</i> L.) forest as well as in grassland areas. The P status was assessed by conventional methods and by isotope dilution kinetics. We found that P concentrations and stocks, as well as their distribution through the soil profile, were rather homogeneous at the s...
Distributions of fine root length and mass with soil depth in natural ecosystems of southwestern Siberia
Plant and Soil, 2015
AimsForest-steppe and sub-taiga, two main biomes of southwestern Siberia, have been predicted to ... more AimsForest-steppe and sub-taiga, two main biomes of southwestern Siberia, have been predicted to shift and spread northward with global change. However, ecological projections are still lacking a description of belowground processes in which fine roots play a significant role. We characterized regional fine root patterns in terms of length and mass comparing: 1) sites and 2) vegetation covers.MethodsWe assessed fine root length and mass down to one meter in aspen (Populus tremula) and in grassland stands on six sites located in the forest-steppe and sub-taiga zones and presenting contrasting climate and soil conditions. We distinguished fine roots over diameter classes and also between aspen and understorey in forest. Vertical fine root exploration, fine root densities and total length and mass were computed for all species. Morphological parameters were computed for aspen.ResultsIn both forest and grassland, exploration was deeper and total length and mass were higher in forest-steppe than in sub-taiga. Exploration tended to be deeper in forest than in grassland and for trees than for understorey vegetation within forest stands.ConclusionsThe differences in rooting strategies are related with both pedo-climatic conditions and vegetation cover. Further investigations on nutrient and water availability and on fine root dynamics should permit a better understanding of these patterns and help predicting their future with global changes.
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Papers by Bernd Zeller