• Energy Research

Effects of increasing rainfall variability and weather extremes on litter decomposition are still uncertain, especially in agroecosystems, where the functional structure of soil communities is already affected. We conducted a mesocosm experiment to evaluate the impacts of different rain regimes and land management on litter mass loss and earthworm ecological groups (epigeic, endogeic and anecic) across European agroecosystems. We also tested if the effects of different rainfall regimes (normal, drought, flooding, intermittent) on earthworm functional diversity (FD) or community-weighted mean (CWM) of earthworm ecological groups (particularly anecic species in the case of CWM), affected litter mass loss across land-use types. We found that drought was the main factor retarding litter mass loss across European agroecosystems irrespective of management type. The effects of the rain regime on litter mass loss were coupled with the pedoclimatic conditions that were different among the studied European land-use types. Across land-use types the importance of earthworm communities for litter decomposition was higher under water depletion. These results also suggest that FD, as a proxy of niche complementarity, is crucial for the stability of the decomposition process under environmental disturbances. The FD values under drought regimes strongly indicated that climatic changes may slow down litter decomposition as a result of FD alterations that could compromise the long-term maintenance of litter mass loss. This result may be especially relevant for the European soils that are already under hydric stress, such as in most Mediterranean agroecosystems.

AbstractProjected climate change and rainfall variability will affect soil microbial communities, biogeochemical cycling and agriculture. Nitrogen (N) is the most limiting nutrient in agroecosystems and its cycling and availability is highly dependent on microbial driven processes. In agroecosystems, hydrolysis of organic nitrogen (N) is an important step in controlling soil N availability. We analyzed the effect of management (ecological intensivevs. conventional intensive) on N-cycling processes and involved microbial communities under climate change-induced rain regimes. Terrestrial model ecosystems originating from agroecosystems across Europe were subjected to four different rain regimes for 263 days. Using structural equation modelling we identified direct impacts of rain regimes on N-cycling processes, whereas N-related microbial communities were more resistant. In addition to rain regimes, management indirectly affected N-cycling processes via modifications of N-related microbial community composition. Ecological intensive management promoted a beneficial N-related microbial community composition involved in N-cycling processes under climate change-induced rain regimes. Exploratory analyses identified phosphorus-associated litter properties as possible drivers for the observed management effects on N-related microbial community composition. This work provides novel insights into mechanisms controlling agro-ecosystem functioning under climate change.

The functional trait framework provides a powerful corpus of integrated concepts and theories to assess how environmental factors influence ecosystem functioning through community assembly. While common in plant ecology, this approach is under-used in microbial ecology. After an introduction of this framework in the context of microbial ecology and enzymology, we propose an approach 1) to elucidate new links between soil microbial community composition and microbial traits; and 2) to disentangle mechanisms underlying “total” potential enzyme activity in soil (sum of 7 hydrolase potential activities). We address these objectives using a terrestrial grassland ecosystem model experiment with intact soil monoliths from three European countries (Switzerland, France and Portugal) and two management types (Conventional-intensive and Ecological-intensive), subjected to 4 rain regimes (Dry, Wet, Intermittent and Normal) under controlled conditions in a common climate chamber. We found tight associations between proxies of microbial ecoenzymatic community-weighted mean traits (enzymatic stoichiometry and biomass-specific activity) and community composition, bringing new information on resource acquisition strategy associated with fungi, Gram positive and Gram negative bacteria. We demonstrate that microbial biomass explained most of the total enzyme activity before altered rain regimes, whereas adjustments in biomass-specific activity (enzyme activity per unit of microbial biomass) explained most variation under altered rain regime scenarios. Furthermore, structural equation models revealed that the variation of community composition was the main driver of the variation in biomass-specific enzyme activity prior to rain perturbation, whereas physiological acclimation or evolutionary adaptation became an important driver only under altered rain regimes. This study presents a promising trait-based approach to investigate soil microbial community response to environmental changes and potential consequences for ecosystem functioning. We argue that the functional trait framework should be further implemented in microbial ecology to guide experimental and analytical design.