The capacity of sustainable soil management to protect soil biodiversity and multifunctionality against future droughts and heatwaves in Europe

The buffering capacity of Sustainable Soil Management (SSM) against the negative effects of climate change on soil health remains poorly understood, largely due to the difficulty of conducting regional-scale field studies. We addressed this limitation by studying SSM's ability to mitigate drought and heatwave impacts across six European sites (five arable, one grassland) in 2022–2023. Climate projections from 11 EURO-CORDEX models guided the realistic field simulations using rainout shelters and infrared heaters. At each site, we compared conventionally managed (CON) fields (either high-input croplands in five sites, or low-species diversity grasslands in one site) with adjacent sustainably managed (SUS) fields (organic croplands, mixed-species grasslands). Using biomarker-based methods, we quantified soil biomass and biodiversity (prokaryotes, eukaryotes) and assessed soil multifunctionality (physical/biochemical properties), and the correlations between these two groups of variables. We found that site was the dominant driver of biodiversity (11–79% of variance), while management effects were site-dependent (up to 10%). Climate stressors significantly reduced alpha diversity and co-occurrence network metrics across soil communities, with eukaryotes being more strongly affected than prokaryotes. Essential soil functions, including total available nitrogen, water holding capacity (WHC), and degradable carbon, were also impaired by climate treatment. Importantly, SUS buffered some of these deleterious effects. SUS vs CON soils had less severe reduction in soil water content during drought; eukaryotic and fungal alpha diversity was higher and remained stable after drought; protist biomass remained stable after droughts and heatwaves. Correlations between microbial taxa and both WHC and carbon stock were consistently higher in SUS soils across all climatic conditions. We identified a subset of taxa highly correlated with soil functions in a management and climate-stress-specific way. Region-specific analyses showed that three sites had consistent stability of the soil communities to climate change in the SUS soils, while the other three sites showed either a more predominant effect of climate stressor than soil management, or a decreased stability in response to climate treatment in the SUS soils. Our results provide an evidence base for developing recommendations on soil management regimes to buffer climate change effects on soil biodiversity and multifunctionality.