• Energy Research
• 2021-2025close
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It remains unclear how soil microbes respond to labile organic carbon (LOC) inputs and how temperature sensitivity ($Q_{10}$) of soil organic matter (SOM) decomposition is affected by LOC inputs in a short-term. In this study, $^{13}$C-labeled glucose was added to a pristine grassland soil at four temperatures (10, 15, 20, and 25 ◦C), and the immediate utilization of LOC and native SOM by microbes was measured minutely in a short-term. We found that the LOC addition stimulated the native SOM decomposition, and elevated temperature enhanced the intensity of microbial response to LOC addition. The ratio between microbial respiration derived from LOC and native SOM increased with higher temperature, and more LOC for respiration. Additionally, LOC addition increased the $Q_{10}$ of SOM decomposition, and the $Q_{10}$ of LOC decomposition is higher than that of native SOM. Overall, these findings emphasize the important role of temperature and LOC inputs in soil C cycles.

<p>Global warming is leading to increased temperatures, accentuated evaporation of terrestrial water and increased the atmosphere moisture content, resulting in frequent droughts and heavy precipitation events. It necessary to assess the sensitivity of soil organic carbon (SOC) under storing practices in response to increasing soil moisture, temperature and frequent dry-wet cycles in order to anticipate future soil carbon losses. We evaluated the impact of these climatic events through an incubation experiment on temperate luvisols from conservation agriculture, organic agriculture, organic waste products applications, i.e. biowaste, residual municipal solid waste and farmyard manure composts compared with conventionally managemed soils. The alternative management options all have led to increased SOC stocks. Soil samples were incubated in the lab under different temperatures (20, 28 and 35°C), different moisture conditions (pF1.5; 2.5 and 4.2) and under dry(pF4.2)-wet (pF1.5) cycles. Dry-wet cycles caused CO2 flushes but overall did not stimulate soil carbon mineralization relative to wet controls (pF1.5 and pF2.5). Overall the additional SOC stored under alternative management options was not more sensitive to climate change (temperature, moisture, dry-wet cycles) than the existing SOC.</p>

The severity of drought is predicted to increase across Europe due to climate change. Droughts can substantially impact terrestrial nitrogen (N) cycling and the corresponding microbial communities. Here, we investigated how ammonia-oxidizing bacteria (AOB), archaea (AOA), and complete ammonia oxidizers (comammox) as well as inorganic N pools and N2O fluxes respond to simulated drought under different cropping systems. A rain-out shelter experiment was conducted as part of a long-term field experiment comparing cropping systems that differed mainly in fertilization strategy (organic, mineral, or mixed mineral and organic) and plant protection management (biodynamic versus conventional pesticide use). We found that the effect of drought varied depending on the specific ammonia-oxidizing (AO) groups and the type of cropping system. Drought had the greatest impact on the structure of the AOA community compared to the other AO groups. The abundance of ammonia oxidizers was also affected by drought, with comammox clade B exhibiting the highest sensitivity. Additionally, drought had, overall, a stronger impact on the AO community structure in the biodynamic cropping system than in the mixed and mineral-fertilized conventional systems. The responses of ammonia-oxidizing communities to drought were comparable between bulk soil and rhizosphere. We observed a significant increase in NH4+ and NO3− pools during the drought period, which then decreased after rewetting, indicating a strong resilience. We further found that drought altered the complex relationships between AO communities and mineral N pools, as well as N2O fluxes. These results highlight the importance of agricultural management practices in influencing the response of nitrogen cycling guilds and their processes to drought. Soil Biology and Biochemistry, 201 ISSN:0038-0717 ISSN:1879-3428

Climate change is a fundamental process affecting terrestrial ecosystems. However, there is relatively little knowledge about its impacts on soil communities, with a large degree of uncertainty regarding their resistance to predicted alterations in temperature and, particularly, precipitation. Moreover, most studies exploring the response of soil biota to predicted rainfall reduction have focused on mesic environments and soil microbes, which limit our ability to find general patterns across ecosystems and soil organisms. In this study, we analysed the impact of predicted climate change scenarios of rainfall reduction on soil food webs of Mediterranean water-limited forests using nematodes as bioindicators. We took advantage of replicated rainfall exclusion infrastructures (30% exclusion) established in Quercus forests of southern Spain in 2016 (2-year exclusion) and of southern France in 2003 (15-year exclusion) to explore the sensitivity of the soil food web to predicted reductions at short- and long-term scales. Rainfall reduction had large negative short-term effects on nematode abundance, particularly of lower trophic groups (bacterivores and fungivores). Rainfall reduction had also consistent short- and long-term impacts on community composition (decrease of fungivores, marginal increase of omnivores) and nematode-based indicators of soil food web structure (higher maturity and structure index, lower prey:predator ratio). These results can be considered indicative of a low resistance of the soil food web to rainfall reductions predicted by climate change. Overall, our findings demonstrate the sensitivity of water-limited forests to further reductions in soil water availability, which might substantially alter their soil communities and likely affect the many ecosystem processes that they control. Ministerio de Ciencia, Innovación y Universidades CGL2014-56739-R, RTI2018-094394-B-I00 European Commission. Fondo Social Europeo RYC-2017-23666 Analyses et Expérimentations pour les Ecosystèmes (AnaEE) ANR-11-INBS-0001 Ministerio de Economía y Competitividad PID2019-108288RA-I00 Observatoire de REcherche Montpelliérain de l’Environnement UMS 3282

Plant communities comprising species with different growth strategies and belonging to different functional groups can ensure stable productivity under variable climatic conditions. However, how plant communities can influence the response of nitrogen (N) cycling, in particular, soil microbial N cycling communities, N leaching and N2O fluxes under flooding, and their capacity to suppress flooding-induced N2O fluxes, remains unresolved. The aim of this study was to examine the effect of different plant communities composed of grasses and/or legumes on N cycling soil microorganisms and N2O fluxes, and how these effects are influenced by flooding. Our field experiment consisted of monocultures and two- and four-species mixtures of two grass and two legume species with different growth strategies (slow- and fast-growing species), grown in a fertilised sandy soil in the Netherlands. One year after plant establishment, we imposed paired control and flooding treatments for three weeks. We found that flooding significantly reduced plant N uptake and increased N2O fluxes. This increase was associated with higher abundances of N cycling microbial communities (except for ammonia-oxidising bacteria). Legume presence increased N2O fluxes, irrespective of the legume growth strategy or flooding, but this was not driven by changes in N cycling microbial communities; instead, it was related to an increase in soil nitrate availability. Mixing grasses with legumes promoted high plant N uptake and reduced N losses under control and flooded conditions, in particular when combining slow-growing species, and in the four-species mixture. Our results show that flooding exerted a strong influence on N cycling by increasing N leaching, N2O fluxes, microbial community abundances and decreasing plant N uptake. However, plant communities with slow-growing strategy had lowest relative abundance of nosZII bacteria and ameliorated flooding effects by both reducing N losses and enhancing plant N uptake.

Soil organisms play a major role on litter decomposition process and nutrient cycling in forest ecosystems. These organisms are extremely sensitive to environmental conditions such as soil temperature and moisture conditions which control their demographic parameters and activity. The ongoing climate change can therefore directly affect soil biota communities and the processes they drive. Besides, climate change can also indirectly affect soil biota by altering tree functional traits (e.g., N, Ca, Mg, water holding capacity) with cascading effects on the litter quality. The aim of this study was to determine the relative effects of increased drought and litter type on microbial biomass (bacteria and fungi) and mesofauna abundance (Collembola and Acari) in three experimental sites representative of the three main forests encountered in the northern part of the Mediterranean Basin (dominated by either Quercus pubescens, Quercus ilex or Pinus halepensis) where rainfall exclusion experiments were taking place. At each site, and in each precipitation treatment (natural and amplified drought plots), we collected and transplanted foliage litters (i.e., species × drought level). After two years, we reported a litter species effect: Q. pubescens litter presented consistently the higher abundance of all soil biota groups compared to Q. ilex and P. halepensis litters in each forest. Surprisingly, despite that the amplified drought treatment induced a modification of the litter quality, we did not reported an indirect reduced precipitation effect on soil biota parameters. While Oribatid Acari abundance decreased with amplified drought in all three forest types, the direct effects on the other soil biota groups were forest-dependent. In P. halepensis forest, amplified drought resulted in higher bacterial and fungal biomasses but lower Collembola abundance. In Q. ilex forest both Collembola and predatory Acari abundances decreased with amplified drought. In addition, the positive relationships between Collembola and Oribatida abundances and litter mass loss disappeared under amplified drought conditions in both Q. ilex and P. halepensis forests. These results suggest a key role played by Ca, Mg, specific leaf area (SLA) and water holding capacity (WHC) as drivers of soil biota parameters. Finally, the study highlights that within the same Mediterranean region, climate change could differently alter the soil organisms inhabiting the litter layer and their contributions to the decomposition process depending on the tree species and soil biota group considered.