Trait‐based responses of soil nematode communities to land use and climate change

Abstract The impacts of land use and climate change on soil biota have attracted increasing attention because soil organisms are crucial for nutrient cycling, carbon storage and production. While previous research focused mainly on the taxonomic diversity of soil organisms, trait‐based diversity remains largely unexplored, limiting our understanding of how traits are assembled in response to environmental changes. Here, we investigated the traits (body size, length and diameter) of soil nematodes—the most abundant animals on Earth—at the Global Change Experimental Facility, comparing two land uses (conventional farming and extensively‐used meadow) under ambient and future climate (+0.6°C mean temperature, −20% summer precipitation, +10% spring/autumn precipitation). Beyond mean trait values, we explored upper and lower trait limits, skewness and kurtosis to describe the shape of trait distributions across trophic levels. At the community level, future climate restricted the occurrence of nematodes with small body size, induced a more narrowed trait distribution in croplands and resulted in an even trait distribution in grasslands. At low trophic levels (bacterivores and fungivores), the proportion of shorter and larger individuals was higher in croplands, while longer and smaller ones were more common in grasslands, suggesting a land‐use–dependent trade‐off in body shape. At high trophic levels (omnivores and carnivores), future climate reduced mean body size mainly through declines in the lower trait limits, indicating a strong role of environmental filtering. Mean body size increased with critical pore diameters, but the reasons for this association might be indirect. Synthesis and applications . By linking nematode traits to soil moisture and soil pore structure, our findings show that the effect of future climate on nematode body traits is land‐use dependent, likely reflecting stronger bottom‐up or top‐down regulation in croplands and grasslands, respectively. This trait‐based approach offers a practical framework for using nematode body size distributions and soil pore metrics as early‐warning indicators of soil food web degradation and can inform land management strategies that maintain soil biodiversity and ecosystem functions.