Varying impacts of land-use on the diversity of parasitic nematodes associated with soil metazoan hosts among climatic regions

Soil serves as an important reservoir for metazoan parasites, such as nematodes, many of which parasitize small invertebrates. However, the factors influencing parasitic nematode biogeography and how variations in climate and land-use intensity affect them are still not well understood. This study aims to explore how the diversity and community structure of parasitic nematodes respond to land-use changes across a climatic gradient from subtropical to temperate regions in China. Using high-throughput sequencing (metabarcoding), we analyzed the taxon richness and community composition of parasitic nematodes and their potential metazoan hosts across four land-use types—forest, park, residential area, and farmland—and three climatic zones—subtropical, warm-temperate, and mid-temperate. Our findings indicated that land-use did not affect the richness of parasitic nematodes in the warm-temperate region. However, in subtropical and mid-temperate regions, which are characterized by higher precipitation and biodiversity, intensive land-use significantly decreased parasitic nematode richness, mainly due to a decline in metazoan host richness. Notably, in the subtropical region, changes in soil pH and moisture levels were also linked to reduced parasite richness in human land-use systems, suggesting more complex mechanisms at play. Furthermore, land-use did not lead to biotic homogenization of parasitic nematode communities. Instead, the primary impacts were local extinctions of species and reduced biodiversity associations between parasites and potential hosts. Overall, our study demonstrates that human land-use and climate interact to influence the diversity, composition, and host associations of parasitic nematodes. These findings highlight how land-use changes reduce the biodiversity linkage between parasites and host communities within soil ecosystems.