Low‐intensity land‐use enhances soil microbial activity, biomass and fungal‐to‐bacterial ratio in current and future climates

Abstract Progressing climate change and intensified land‐use exert unprecedented pressures on soil microbial communities, thus endangering the essential ecosystem functions they provide. However, these global change factors do not act in isolation from each other, making ecosystem consequences hard to predict. To address this knowledge gap, we tested the interactive effects of climate change and land‐use intensity on soil microbial activity, biomass and community composition in a large‐scale field experiment. We tested soil microbial responses to a future climate scenario (ambient climate vs. increased temperature by +0.6°C and altered rainfall patterns) in two land‐use types (cropland vs. grassland) with two levels of land‐use intensity each (high‐intensity vs. low‐intensity). While high‐intensity land‐use is characterized by fertilization and pesticide use, low‐intensity land‐use refrains from both. We measured soil microbial activity and biomass twice per year within a 5‐year period and used phospholipid fatty acid analysis to explore changes in microbial community composition. In contrast to our expectations, soil microbes remained largely unaffected by future climate conditions. However, we found evidence that not just the type of land‐use, but also their respective management intensity (high vs. low) had strong effects on soil microbes. Low‐intensity management promoted soil microbial activity and biomass in grasslands, but this beneficial effect needed several years to establish. Moreover, we show that low‐intensity management increased AM fungi and fungal‐to‐bacterial ratios in croplands as well as grasslands. Our study shows that farmers can promote soil ecosystem functions through low‐intensity management measures. In grasslands, low‐intensity management measures such as high plant diversity consisting of grasses, forbs and legumes, and no mineral fertilization improve soil microbial activity and biomass, as well as the fungal‐to‐bacterial ratio. On arable land, compliance with EU organic farming regulations improves the fungal‐to‐bacterial ratio. We conclude that low‐intensity management can have positive effects on efficient carbon storage, nutrient cycling, soil erosion control and ecosystem multifunctionality under different land‐use and climate change scenarios.