Negative Effects of Copper Oxide Nanoparticles on Carbon and Nitrogen Cycle Microbial Activities in Contrasting Agricultural Soils and in Presence of Plants

Metal-oxide nanoparticles (NPs) such as copper oxide (CuO) NPs offer promising perspectives for the development of novel agro-chemical formulations of pesticides and fertilizers. However, their potential impact on agro-ecosystem functioning still remains to be investigated. Here, we assessed the impact of CuO-NPs (0.1, 1, and 100 mg/kg dry soil) on soil microbial activities involved in the carbon and nitrogen cycles in five contrasting agricultural soils in a microcosm experiment over 90 days. Additionally, in a pot experiment, we evaluated the influence of plant presence on the toxicity of CuO-NPs on soil microbial activities. CuO-NPs caused significant reductions of the three microbial activities measured (denitrification, nitrification, and soil respiration) at 100 mg/kg dry soil, but the low concentrations (0.1 and 1 mg/kg) had limited effects. We observed that denitrification was the most sensitive microbial activity to CuO-NPs in most soil types, while soil respiration and nitrification were mainly impacted in coarse soils with low organic matter content. Additionally, large decreases in heterotrophic microbial activities were observed in soils planted with wheat, even at 1 mg/kg for soil substrate-induced respiration, indicating that plant presence did not mitigate or compensate CuO-NP toxicity for microorganisms. These two experiments show that CuO-NPs can have detrimental effects on microbial activities in soils with contrasting physicochemical properties and previously exposed to various agricultural practices. Moreover, we observed that the negative effects of CuO-NPs increased over time, indicating that short-term studies (hours, days) may underestimate the risks posed by these contaminants in soils

Four years of experimental climate change modifies the microbial drivers of N2O fluxes in an upland grassland ecosystem

International audienceEmissions of the trace gas nitrous oxide (N2O) play an important role for the greenhouse effect and stratospheric ozone depletion, but the impacts of climate change on N2O fluxes and the underlying microbial drivers remain unclear. The aim of this study was to determine the effects of sustained climate change on field N2O fluxes and associated microbial enzymatic activities, microbial population abundance and community diversity in an extensively managed, upland grassland. We recorded N2O fluxes, nitrification and denitrification, microbial population size involved in these processes and community structure of nitrite reducers (nirK) in a grassland exposed for 4 years to elevated atmospheric CO2 (+200 ppm), elevated temperature (+3.5 °C) and reduction of summer precipitations (−20%) as part of a long-term, multifactor climate change experiment. Our results showed that both warming and simultaneous application of warming, summer drought and elevated CO2 had a positive effect on N2O fluxes, nitrification, N2O release by denitrification and the population size of N2O reducers and NH4 oxidizers. In situN2O fluxes showed a stronger correlation with microbial population size under warmed conditions compared with the control site. Specific lineages of nirK denitrifier communities responded significantly to temperature. In addition, nirK community composition showed significant changes in response to drought. Path analysis explained more than 85% of in situN2O fluxes variance by soil temperature, denitrification activity and specific denitrifying lineages. Overall, our study underlines that climate-induced changes in grassland N2O emissions reflect climate-induced changes in microbial community structure, which in turn modify microbial processe

Short-term plant legacy alters the resistance and resilience of soil microbial communities exposed to heat disturbance in a Mediterranean calcareous soil

International audiencePlant legacy is a concept representing the effects exerted by plants on soil once they are no longer growing. We hypothesized that plant species and mixture (intercropping) would induce different short-term legacy effects impacting carbon and nitrogen-related soil microbial activities and resistance and resilience after a heat disturbance. A microcosm experiment was conducted using a calcareous Mediterranean soil conditioned by a complete vegetative cycle in a greenhouse with four planting modalities (W = monoculture of Wheat (Triticum aestivum L.); L = monoculture of white Lupin (Lupinus albus L.); WL = both species intercropped; U = unplanted soil). Half of microcosms were incubated at 28 °C (C = control conditions) whereas the remaining half were exposed at 48 °C for 2 days (S = stress conditions), with an immediately return to control conditions. Microcosms were destructively sampled at 2, 7, 16 and 28 days (T2, T7, T16, T28) after the end of the heat disturbance and the following soil measurements were performed: Basal Respiration (BR), Substrate-Induced Respiration (SIR), Nitrification Enzyme Activity (NEA) and N mineral concentrations. Our results demonstrated that monocultures and intercropping promoted different legacy effects under control conditions especially for SIR. WL soils presented lower values of SIR than L and higher than W soils. For SIR, W and WL soils conferred greater resistance to the heat stress, whereas L and WL soils conferred higher resilience at T28. For NEA, no differences between soils were observed for resistance to heat stress, but at T16, soils having WL legacy were more resilient than L soils, but comparable to those having W legacy. Our results highlight that a short-term legacy effect is measurable but greatly differs between C- and N-related microbial activities. We estimated that intercropping had modified ability of soil microorganisms to face heat stress, suggesting that plant legacy effect has to be considered to mitigate extreme climatic events in Mediterranean soils

Appendix C. The effect of plants and fertilization on soil parameters in adherent soil (NO3- and NH4+ concentrations).

The effect of plants and fertilization on soil parameters in adherent soil (NO3- and NH4+ concentrations)

Appendix B. Plant position on the conservative vs. exploitative plants gradient in unfertilized and adherent soil data.

Plant position on the conservative vs. exploitative plants gradient in unfertilized and adherent soil data

Appendix A. Residual maximum likelihood (REML) results of the influence of plant traits (physiological and belowground and whole plant traits), as explanatory factors on key microbial parameters (DEA and NEA) in adherent soil.

Residual maximum likelihood (REML) results of the influence of plant traits (physiological and belowground and whole plant traits), as explanatory factors on key microbial parameters (DEA and NEA) in adherent soil