Microhabitat properties explain variations in soil nematode communities across climate conditions in cropland, but not in grassland

Soil nematodes are valuable bioindicators for the ecological status of soils. Nematode community properties are known to be altered by land-use intensity, to vary with seasonal dynamics, and to be affected by climate change. These external drivers also affect a range of structural, physical, and biochemical soil properties. However, it is unclear whether shifts in nematode community properties are the result of changing resource accessibility in the soil or whether these just co-occur. Here, we linked nematode community to microhabitat properties of intact soils and biochemical properties of bulk soils from a long-term field trial on land-use intensity (cropland vs. grassland) and simulated climate change (ambient vs. future climate). Soil samples were taken in two seasons (November vs. June) to capture a wide range of climatic conditions. The objective of the study was to investigate whether the resource accessibility imposed by microhabitat properties would regulate nematode communities and whether the strength of bottom-up regulation depended on climate change, land use intensification, seasonality and their interactions. Land-use and seasonality had clearly separable effects on nematode community composition. The coupling of physical microstructure properties with nematode community properties depended on land use. In cropland, nematode abundance was strongly associated with the features of the habitable pore space, such as nematode-specific porosity, pore connectivity, and particulate organic matter. Grassland nematode communities were independent of these measurable habitat properties and featured stronger co-occurrence networks. The effect of increased temperature and shifting precipitation patterns on nematode community properties were generally smaller, varied with land use and season, and were not linked to concomitant changes in microhabitat properties. Our findings indicate that characterizing microhabitat properties might be a promising approach to help explain the notorious variability in nematode community composition. The strength of bottom-up regulation by resource accessibility could be a valuable indicator of the resilience of nematode communities to environmental stresses and perturbations. • Higher nematode abundance & stronger co-occurrence network in grass-than cropland. • Microhabitat properties and resource availability enhanced under grassland. • Nematode abundance was tightly linked to microhabitat properties under cropland. • This bottom-up regulation through resource accessibility was weak in grassland. • Climate effect on nematode abundance and community composition was weak.