Local environmental conditions shape the soil micro-food web in Mediterranean grasslands stronger than plant functional groups

Aim Belowground ecosystems in grasslands are influenced by the aboveground plant community, but interactions between local environmental conditions and plant type remain unclear. To address this, the soil micro-food webs were examined in grassland monocultures of three plant functional groups (grasses, legumes, forbs) in different Mediterranean regions. Methods At sites in Spain, France and Slovenia, soil properties and the structure and function of microbial and nematode assemblages were examined in autumn and spring in consecutive seasons. The differences in micro-food web composition were assessed, and related to site characteristics and plant type. Results The micro-food webs differed by regions, with the Slovenian soil comprising the highest biomass of microbial groups, which was linked to high soil organic carbon content. Correspondingly, bacterial-feeding nematodes dominated here and in French soils. A prolonged drought at the Spanish site resulted in high proportions of Gram-positive bacteria, saprotrophic fungi, and plant parasitic nematode, while higher food web levels were scarce. Dry conditions further increased the strength of trophic links between nematodes and their microbial food resource. In contrast, plant functional groups had only minor impact on the micro-food webs across sites and seasons. Conclusions This study highlights that local pedo-climate, rather than plant species identity, shapes the micro-food webs in Mediterranean grasslands. Conditions at the Spanish site allow to pinpoint the consequences of drought stress, suggesting an increase in plant parasites alongside with hampered top-down control by predators, which can have cascading negative effects on plant growth.