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N2O contributes to increasing the greenhouse effect and is also involved in stratospheric ozone depletion. In soil and water, N2O reductase catalyses the reduction of N2O into the inert form N2. N2O reductase activity is known to be affected by acidic conditions and the application of liming materials to acidic soils is now proposed as a solution for mitigating soil N2O emissions. During a one-year laboratory experiment, we studied the functioning of N2O reductase after the application of calcium carbonates to an acidic soil with a very low capacity to reduce N2O. The functioning of N2O reductase was characterised through anaerobic incubations using the acetylene inhibition technique combined with a logistic model to determine the main enzyme functioning characteristics (latency, maximal rate). Both changes in soil pH and soil capacity to reduce N2O were rapidly observed after the application of lime materials. The activity of N2O reductase was observed to be efficient throughout the experiment even when the soil had returned to initial acidic conditions, revealing a hysteretic response of N2O reductase to pH variations. Nevertheless, some signs of lower N2O reductase activity over time were observed mainly after 200 days of applying lime materials. Altogether, these results suggest that, in this soil condition, the beneficial impact of the application of liming materials on N2O emissions could last longer than this on soil pH. [ABSTRACT FROM AUTHOR]

Shifts in the frequency and magnitude of rain events (precipitation patterns) associated with climate change may impact ecosystem nitrogen and carbon cycling through effects on plant physiology and soil microbial activity. Here, we determined how the combination of temporal irrigation distribution and N supply affects plant-microbial C and N dynamics in microcosms with winter wheat. First, we investigated legacy effect of 12 weeks of contrasting irrigation distribution (frequent and small versus infrequent and large water inputs) and N inputs (high versus low) on plant biomass, organic and inorganic N pools, and potential nitrification and denitrification rates. Second, we investigated legacy effects of these treatments on C and N fluxes in plants and microbes over 29 h after a rewetting event, using 13C-CO2 and 15N-NH4 labeling. We found that irrigation distribution and N input led to significant differences in plant responses and soil C input, setting the scene for the rewetting response. Immediately after rewetting, microorganisms outcompeted plants for soil mineral N. However, over time, the net outcome of competition improved for plants regardless of water or N input history. Further, we found that a history of frequent irrigation led to more productive plants (biomass and rate of photosynthesis) and increased their net competitiveness for N over microorganisms. This suggests that the shift toward more extreme fluctuations in soil moisture predicted by climate forecasts for most temperate zones may have negative implications for plant productivity due to altered N dynamics between plants and soil microorganisms. [ABSTRACT FROM AUTHOR]

Climate change models predict shifts in the frequency and magnitude of rain events (precipitation patterns). We studied how precipitation history shapes microbial community responses to rewetting and how these effects depend on N status. Twelve weeks of contrasting precipitation and N input left a legacy effect by shaping present (DNA-based) and potentially active (rRNA-based) bacterial and fungal communities. This legacy effect determined the microbial response to rewetting, as demonstrated by differences in the post-wet potentially active bacterial and fungal communities as well as the flux of soil-emitted CO 2 over a 29-h period. Despite contrasting effects of precipitation and N input history on fungal:bacterial ratio and microbial community composition, the timing of the potentially active bacterial and fungal response to rewetting was not altered. Thus, regardless of precipitation or N input history, potentially active bacteria responded with a small shift in community composition within 1 h of rewetting but did not change further for the remaining 28 h analyzed. The potentially active fungi did not respond to rewetting within 29 h. Even though more extreme fluctuations in soil moisture changed soil microbial community composition, the short-term response of microbial communities to rewetting was conserved. Soil CO 2 efflux upon rewetting was higher from systems with a history of frequent precipitation and underline the role of plants in drying-rewetting processes. We suggest that shifts in the fungal:bacterial ratio, as well as N-cycling potentials, may have consequences on food web stability and soil biogeochemical cycling. • Precipitation and N input legacy shaped soil bacterial and fungal communities. • Soils with a frequent precipitation legacy emitted more CO 2 upon rewetting. • The potentially active bacterial community shifted regardless of legacy. • Fungal communities did not respond to rewetting (assessed over 29-h). [ABSTRACT FROM AUTHOR]

Purpose: The main goal of this study was to determine if ancient wheat varieties could store more carbon than modern ones in the presence or absence of inputs, due to a likely bigger and deeper root system and a slower mineralization rate. Methods: We conducted a field experiment with four modern and four ancient varieties (released before 1960 and often grown without inputs), with and without chemical inputs (nitrogen, herbicide and fungicide taken as a single factor). Root morphology was assessed by image analysis, potential catabolic activities of fructose, alanine, citric acid by MicroResp™ and overall CO2 emissions by incubating soil and roots from each modality for 60 days. Results: The breeding type did not affect root traits, substrates respiration nor CO2 emissions in our environmental conditions. The application of inputs did not affect root traits but influenced the respiration of specific substrates and CO2 emissions. The most noticeable response was due to the "breeding type x inputs" interaction: inputs increased CO2 emissions from soil and root tissues of ancient varieties by 19%, whereas no effect was observed for modern varieties. Conclusion: Taken together, our results did not support the hypothesis that ancient varieties could be more performant than modern ones in storing carbon in our experimental conditions. Increased CO2 emissions by ancient varieties in the presence of inputs showed that ancient and modern varieties differed in their phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Agriculture is the main source of terrestrial N2O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase gene ( nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2O-reducers ( nos ZII) was related to the potential capacity of the soil to act as a N2O sink. However, little is known about how this group responds to different agricultural practices. Here, we investigated how N2O-producers and N2O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2O emissions. The abundance of both ammonia-oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N2O emissions were also assessed. Overall, greatest differences in microbial activity, diversity, and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N2O emissions, we subdivided more than 59,000 field measurements into fractions from low to high rates. We found that the low N2O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nos ZII clade but not of the nos ZI clade was important to explain the variation of in situ N2O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2O-reducing bacteria to agricultural practices and how it may ultimately affect N2O emissions. [ABSTRACT FROM AUTHOR]

Microbial communities have a central role in ecosystem processes by driving the Earth's biogeochemical cycles. However, the importance of microbial diversity for ecosystem functioning is still debated. Here, we experimentally manipulated the soil microbial community using a dilution approach to analyze the functional consequences of diversity loss. A trait-centered approach was embraced using the denitrifiers as model guild due to their role in nitrogen cycling, a major ecosystem service. How various diversity metrics related to richness, eveness and phylogenetic diversity of the soil denitrifier community were affected by the removal experiment was assessed by 454 sequencing. As expected, the diversity metrics indicated a decrease in diversity in the 1/103 and 1/105 dilution treatments compared with the undiluted one. However, the extent of dilution and the corresponding reduction in diversity were not commensurate, as a dilution of five orders of magnitude resulted in a 75% decrease in estimated richness. This reduction in denitrifier diversity resulted in a significantly lower potential denitrification activity in soil of up to 4-5 folds. Addition of wheat residues significantly increased differences in potential denitrification between diversity levels, indicating that the resource level can influence the shape of the microbial diversity-functioning relationship. This study shows that microbial diversity loss can alter terrestrial ecosystem processes, which suggests that the importance of functional redundancy in soil microbial communities has been overstated. [ABSTRACT FROM AUTHOR]