Legacy effects of drought on plant-soil feedbacks and plant-plant interactions

• Interactions between aboveground and belowground biota have the potential to modify ecosystem responses to climate change, yet little is known about how drought influences plant–soil feedbacks with respect to microbial mediation of plant community dynamics. • We tested the hypothesis that drought modifies plant–soil feedback with consequences for plant competition. We measured net pairwise plant–soil feedbacks for two grassland plant species grown in monoculture and competition in soils that had or had not been subjected to a previous drought; these were then exposed to a subsequent drought. To investigate the mechanisms involved, we assessed treatment responses of soil microbial communities and nutrient availability. • We found that previous drought had a legacy effect on bacterial and fungal community composition that decreased plant growth in conspecific soils and had knock-on effects for plant competitive interactions. Moreover, plant and microbial responses to subsequent drought were dependent on a legacy effect of the previous drought on plant–soil interactions. • We show that drought has lasting effects on belowground communities with consequences for plant–soil feedbacks and plant–plant interactions. This suggests that drought, which is predicted to increase in frequency with climate change, may change soil functioning and plant community composition via the modification of plant–soil feedbacks

Soil microbial community responses to heat wave components: drought and high temperature

Heat waves, defined as events associating high temperatures with severe drought, are expected to become increasingly recurrent. Research has focused heavily on the impacts of drought and temperature increase on soil functioning and microbial diversity, but little attention has been paid to soil microbial community responses to combined heat-drought stresses. Heat waves, which combine heat and drought stresses, may induce different microbial responses to those observed in studies focusing on heat or drought alone. Microbial recovery strategies to withstand heat-drought conditions, along with patterns of microbial functional redundancy and complex interactions with the soil physical-chemical-biological interface may have marked effects on soil ecosystem functioning, particularly in agroecosystems through the rhizosphere. To better under stand how heat waves affect soil ecosystem functioning, we advocate the development of mechanistic approaches integrating individual to community level and biophysicochemical studies on the indirect effects of combined heat-drought stresses in microbial communities, observed through soil environment parameters in experimental and field studies. The challenge will be to define trait-based functional indicators of the microbial community response to heat waves, particularly the potential interrelatedness between the traits responsible for tolerance to drought and hea

Nitrogen fertilization reduces the capacity of soils to take up atmospheric carbonyl sulphide

Soils are an important carbonyl sulphide (COS) sink. However, they can also act as sources of COS to the atmosphere. Here we demonstrate that variability in the soil COS sink and source strength is strongly linked to the available soil inorganic nitrogen (N) content across a diverse range of biomes in Europe. We revealed in controlled laboratory experiments that a one-off addition of ammonium nitrate systematically decreased the COS uptake rate whilst simultaneously increasing the COS production rate of soils from boreal and temperate sites in Europe. Furthermore, we found strong links between variations in the two gross COS fluxes, microbial biomass, and nitrate and ammonium contents, providing new insights into the mechanisms involved. Our findings provide evidence for how the soil-atmosphere exchange of COS is likely to vary spatially and temporally, a necessary step for constraining the role of soils and land use in the COS mass budget

Rôle de la diversité microbienne sur la minéralisation de la matière organique du sol

National audienc

How do drought and rain events impact soil microbial communities greenhouse gas production?

International audienc

Influence de la qualité biochimique des résidus végétaux sur les processus de minéralisation et les communautés bactériennes impliquées

National audienc

Oxygen isotope exchange between water and carbon dioxide in soils is controlled by pH, nitrate and microbial biomass through links to carbonic anhydrase activity

International audienceThe oxygen isotope composition of atmospheric carbon dioxide (CO 2) is intimately linked to largescale variations in the cycling of CO 2 and water across the Earth's surface. Understanding the role the biosphere plays in modifying the oxygen isotope composition of atmospheric CO 2 is particularly important as this isotopic tracer has the potential to constrain estimates of important processes such as gross primary production at large scales. However, constraining the atmospheric mass budget for the oxygen isotope composition of CO 2 also requires that we understand better the contribution of soil communities and how they influence the rate of oxygen isotope exchange between soil water and CO 2 (k iso) across a wide range of soil types and climatic zones. As the carbonic anhydrases (CAs) group of enzymes enhances the rate of CO 2 hydration within the water-filled pore spaces of soils, it is important to develop understanding of how environmental drivers can impact k iso through changes in their activity. Here we estimate k iso and measure associated soil properties in laboratory incubation experiments using 44 soils sampled from sites across western Eurasia and northeastern Australia. Observed values for k iso always exceeded theoretically derived uncatalysed rates, indicating a significant influence of CAs on the variability of k iso across the soils studied. We identify soil pH as the principal source of variation, with greater k iso under alkaline conditions suggesting that shifts in microbial community composition or intra-extracellular dissolved inorganic carbon gradients induce the expression of more or higher activity forms of CAs. We also show for the first time in soils that the presence of nitrate under naturally acidic conditions reduces k iso , potentially reflecting a direct or indirect inhibition of CAs. This effect appears to be supported by a supplementary ammonium nitrate fertilisation experiment conducted on a subset of the soils. Greater microbial biomass also increased k iso under a given set of chemical conditions, highlighting a putative link between CA expression and the abundance of soil microbes. These data provide the most extensive analysis of spatial variations in soil k iso to date and indicate the key soil trait datasets required to predict variations in k iso at large spatial scales, a necessary next step to constrain the important role of soil communities in the atmospheric mass budget of the oxygen isotope composition of CO 2

Disentangling the rates of carbonyl sulfide (COS) production and consumption and their dependency on soil properties across biomes and land use types

Soils both emit and consume the trace gas carbonyl sulfide (COS) leading to a soil-air COS exchange rate that is the net result of two opposing fluxes. Partitioning these two gross fluxes and understanding their drivers are necessary to estimate the contribution of soils to the current and future atmospheric COS budget. Previous efforts to disentangle the gross COS fluxes from soils have used flux measurements on air-dried soils as a proxy for the COS emission rates of moist soils. However, this method implicitly assumes that COS uptake becomes negligible and that COS emission remains steady while soils are drying. We tested this assumption by simultaneously estimating the soil COS sources and sinks and their temperature sensitivity (Q(10)); these estimates were based on soil-air COS flux measurements on fresh soils at different COS concentrations and two soil temperatures. Measurements were performed on 27 European soils from different biomes and land use types in order to obtain a large range of physical-chemical properties and identify the drivers of COS consumption and production rates. We found that COS production rates from moist and air-dried soils were not significantly different for a given soil and that the COS production rates had Q(10) values (3.96 +/- 3.94) that were larger and more variable than the Q(10) for COS consumption (1.17 +/- 0.27). COS production generally contributed less to the net flux at lower temperatures but this contribution of COS production increased rapidly at higher temperatures, lower soil moisture contents and lower COS concentrations. Consequently, measurements at higher COS concentrations (viz. 1000 ppt) always increased the robustness of COS consumption estimates. Across the range of biomes and land use types COS production rates co-varied with total soil nitrogen concentrations (r = 0.52, P < 0.05) and mean annual precipitation (r = 0.53, P < 0.05), whilst the gross COS uptake rate and the first-order COS hydrolysis rate constant co-varied significantly with the microbial biomass nitrogen (N) content of the soils (r = 0.74 and 0.64, P < 0.05 and P < 0.05, respectively). Collectively our findings suggest a strong interaction between soil nitrogen and water cycling on COS production and uptake, providing new insights into how to upscale the contribution of soils to the global atmospheric COS budget

Dynamics of soil bacterial populations involved in degradation of 13c-labelled wheat, rape and alfalfa residue as estimated by DNA-SIP technique

International audienc

Measurements of net soil-atmosphere carbon dioxide exchange and its oxygen and carbon isotope composition in incubations of soil sampled from 44 sites in western Eurasia and northeastern Australia

Soils were sampled from 27 sites in western Eurasia during 2016 and 17 sites in northeastern Australia during 2017. Triplicate replicate microcosm incubations were created from homogenised soil from each site. The net soil-atmosphere exchange of carbon dioxide and its oxygen and carbon isotope composition between the soil and atmospheric was measured under two different headspace conditions using a custom built gas-exchange system. Subsequently the pH, microbial biomass and the availability of ammonium and nitrate were determined for incubated soils. An additional fertlisation experiment, consisting of a 0.7 mg addition of ammonium nitrate per gram of dry soil, was conducted on soils from 14 sites. The data from these incubations are reported along with the characteristics of the original sampling sites