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Drought and agricultural management influence soil microorganisms with unknown consequences for the functioning ofagroecosystems. We simulated drought periods in organic (biodynamic) and conventional wheat fields and monitoredeffects on soil water content, microorganisms and crops. Above the wilting point, water content and microbial respirationwere higher under biodynamic than conventional farming. Highest bacterial and fungal abundances were found inbiodynamically managed soils, and distinct microbial communities characterised the farming systems. Most biological soilquality parameters and crop yields were only marginally affected by the experimental drought, except for arbuscularmycorrhizal fungi (AMF), which increased in abundance under the experimental drought in both farming systems. AMFwere further strongly promoted by biodynamic farming resulting in almost three times higher AMF abundance underexperimental drought in the biodynamic compared with the conventional farming system. Our data suggest an improvedwater storage capacity under biodynamic farming and confirms positive effects of biodynamic farming on biological soilquality. The interactive effects of the farming system and drought may further be investigated under more substantialdroughts. Given the importance of AMF for the plant’s water supply, more in-depth studies on AMF may help to clarify theirrole for yields under conditions predicted by future climate scenarios.
Soil invertebrates are key to decomposition, a central ecosystem process related to soil health. In many temperate areas climate change will decrease soil water content, which strongly modulates biological activity. However, data are lacking on how shifts in rainfall patterns affect soil biota and the ecosystem processes they provide. Here, we used the bait-lamina test to experimentally assess how a severe drought event influenced detritivore feeding activity, during a wheat growing season, in soils under long-term organic or conventional farming. Additionally, biotic and abiotic soil parameters were measured. Feeding activity was reduced under extreme drought and conventional management, although no climate-management synergies were found. Vertical migrations of Collembola and Oribatida partially explained the unexpectedly higher bait consumption at shallower depths in response to drought. Exploratory mixed-effects longitudinal random forests (a novel machine learning technique) were used to explore whether the relative abundances of meso‑, microfauna and microbes of the decomposer food web, or abiotic soil parameters, affected the feeding activity of detritivores. The model including meso‑ and microfauna selected four Nematoda taxa and explained higher variance than the model with only microbiota, indicating that detritivore feeding is closely associated with nematodes but not with microbes. Additionally, the model combining fauna and microbiota explained less variance than the faunal model, suggesting that microbe-fauna synergies barely affected detritivore feeding. Moreover, soil water and mineral nitrogen contents were found to strongly determine detritivore feeding, in a positive and negative way, respectively. Hence, our results suggest that severe drought and conventional farming impair the feeding activity of soil detritivores and thus, probably, decomposition and nutrient mineralization in soils. Furthermore, machine learning algorithms arise as a powerful technique to explore the identity of potential key drivers relating biodiversity to ecosystem functioning.
Conventional agriculture and not drought alters relationships between soil biota and functions
(2021)
Soil biodiversity constitutes the biological pillars of ecosystem services provided by soils worldwide. Soil life is threatened by intense agricultural management and shifts in climatic conditions as two important global change drivers which are not often jointly studied under field conditions. We addressed the effects of experimental short‐term drought over the wheat growing season on soil organisms and ecosystem functions under organic and conventional farming in a Swiss long term trial. Our results suggest that activity and community metrics are suitable indicators for drought
stress while microbial communities primarily responded to agricultural practices. Importantly, we found a significant loss of multiple pairwise positive and negative relationships between soil biota and process‐related variables in response to conventional farming, but not in response to experimental drought. These results suggest a considerable weakening of the contribution of soil biota to ecosystem functions under long‐term conventional agriculture. Independent of the farming system, experimental and seasonal (ambient) drought conditions directly affected soil biota and activity. A higher soil water content during early and intermediate stages of the growing season and a high number of significant relationships between soil biota to ecosystem functions suggest that organic farming provides a buffer against drought effects.