Comparison of grassland nematode communities in the European and middle eastern Mediterranean under different forage plants

Summary Grassland ecosystems are key biodiversity reservoirs, especially for the soil fauna. Among them, nematodes have been widely used as bioindicators to assess soil conditions and health in grasslands. However, their interactions with plant functional types, particularly in hot and dry climates like the Mediterranean region, remain poorly understood. The development of management strategies to optimise the resilience and productivity of grassland requires a better understanding of these biotic relationships. To address this, nematode communities were examined in grassland monocultures of three plant functional groups (grasses, legumes, forbs) in the Mediterranean. In France, Slovenia, Spain, Jordan and Lebanon, grasslands differing in soil properties and climate were investigated in autumn and spring in consecutive seasons. The genus composition of nematode assemblages was assessed, and their ecological indices and metabolic footprints were related to site characteristics and plant functional type. The Renkonen and Sörensen Index revealed that nematode communities differed greatly among regions. The western Mediterranean grasslands were dominated by bacterial feeders like Rhabditis and Eucephalobus , resulting in a low Channel Index and high Enrichment Index. The eastern Mediterranean sites showed higher proportions of fungal and plant feeders like Aphelenchus and Geocenamus and a higher Channel Index but lower Enrichment Index. Due to prolonged drought, the Spanish soils were infested by plant feeders such as Scutylenchus and Pratylenchus . The forage plant had only a minor impact, with legumes enhancing certain bacterial-feeding genera and grasses fostering some plant-parasitic nematodes. Overall, regional factors shape the nematode community more than forage plant cover. The dry conditions in the eastern Mediterranean, as well as the drought in Spain, increased herbivores and decreased top-down control, which is relevant in the light of future climate change.