The response of soil macroinvertebrates to alpine meadow degradation in the Qinghai-Tibetan Plateau, China

The alpine meadow in the Qinghai-Tibetan Plateau has degraded in recent years; however, the response of soil macroinvertebrates to the alpine meadow degradation is unknown. We hypothesized that (i) soil macroinvertebrate diversity and abundance decrease gradually during alpine meadow degradation and (ii) the composition of soil macroinvertebrate communities is specific to particular degradation phases. We investigated the soil macroinvertebrates, plant communities and soil properties in a swampy meadow, grassland meadow, moderately degraded meadow and severely degraded meadow to test the hypotheses from April 2009 to October 2011. These areas represent four degradation phases of alpine meadows. The structure of the soil macroinvertebrate community in the moderately degraded meadow was notably different from that of the swampy meadow and the grassland meadow. Most of the macroinvertebrate groups disappeared from the severely degraded meadow. Taxonomic richness and abundance were significantly greater in the moderately degraded meadow and were significantly lower in the severely degraded meadow. Significant seasonal dynamics were only found for taxonomic richness in the moderately degraded meadow. Furthermore, the abundances of Polydesmida and Coleoptera differed significantly between the four habitats, but no significant seasonal changes were observed in the four habitats. The soil macroinvertebrate structures were influenced by the plant and soil variations, particularly the available soil P and K, the pH and vegetation heights, which changed significantly among the habitats. The soil macroinvertebrate taxonomic richness was also significantly correlated with the species richness, species coverage, vegetation height, aboveground biomass of the plant community, bulk density, organic matter, available soil N, P and K and pH. However, the abundances of the soil macroinvertebrate community and Polydesmida were only correlated with the available soil P and K, while Coleoptera was significantly correlated with all measured soil parameters, plant species richness and species coverage. Our results demonstrated that moderate and severe degradation in the alpine meadow have significant effects on the structure, diversity and abundance of soil macroinvertebrate communities, and the available soil P and K, pH and vegetation height are the determining factors. Our results also indicated that the soil macroinvertebrates in moderately degraded meadows will be more easily affected by climate changes in the future.