Effects of grazing on soil nematodes in grasslands: a global meta-analysis.
Abstract
Grazing contributes substantially to grassland degradation worldwide and may alter soil biota and function. However, the effects of grassland type, grazing intensity and duration, and livestock type on soil nematodes are not fully understood. Here, we compiled 783 pair-wise comparisons from 28 publications to better understand the pattern and underlying mechanisms of soil nematodes responses to grazing. Grazing significantly decreased the abundance of bacterial-feeding and omnivorous-predatory nematodes but had no effect on diversity (e.g. generic richness) and ecological indices (e.g. maturity index and plant-parasitic index). Grazing effects on soil nematodes varied strongly by grassland type, grazing intensity and duration, and livestock type. Grazing decreased bacterial-feeding nematodes in steppe. In meadow, grazing increased plant-feeding nematodes and reduced nematode diversity. The abundance of bacterial-feeding and fungal-feeding nematodes significantly decreased in long-term grazing (>10 years). Light grazing increased fungal-feeding nematodes and maturity index. Heavy grazing decreased total nematode abundance, the abundance of all trophic groups except plant-feeding nematodes and the enrichment index. Sheep grazing produced a stronger negative response than cattle grazing on the abundance of bacterial-feeding and omnivorous-predatory nematodes, Shannon-Wiener index and enrichment index. Environment factors and soil properties influenced the grazing effects on nematode abundance. Our results showed that the grazing effects on nematode abundance were well explained by pH and soil organic carbon. Synthesis and applications. Our findings highlight that grazing effects on soil nematodes are context-specific. As the contribution of soil nematodes to grassland management and ecosystem functions, we propose that policymakers should consider devising local-scale grazing strategies for conserving soil biota and the functions of soil food webs.