Effects of alpine meadow degradation on soil insect diversity in the Qinghai-Tibetan Plateau

Abstract

Soil insects are an important component and play a key role in the material cycling and energy flow processes in grassland ecosystems. However, soil insect populations are easily influenced by changes in environmental factors. The Qinghai-Tibetan Plateau is the highest and largest plateau in the world, and is mainly dominated by alpine meadow vegetation. Alpine meadow degradation has become an important, widespread, and growing ecological problem in the Qinghai-Tibetan Plateau due to the effects of climate change and increasing overgrazing. The Zoigê wetland, which is located on the eastern edge of the Qinghai-Tibetan Plateau, has also degraded due to climate change and increased overgrazing over the last 50 years. Currently, there are four typical habitats (swamp meadow, grassland meadow, moderately degraded meadow, and seriously degraded meadow) in this area. However, the changes in the structure and diversity of the soil insect community among the four habitats are unknown. Six plots of 50 cm × 50 cm were selected in each habitat to investigate the effects of alpine meadow degradation on the soil insect community in April, May, July, and October of 2011. A total of 4,172 insect individuals were captured and classified into 8 orders, 35 families, and 46 taxonomic groups. The Sciaridae larvae, Chironomidae larvae, and Curculionidae larvae were the dominant groups in soil insect communities, and Sciaridae larvae comprised the most dominant group at all four degradation phases. The density and diversity indices of the soil insects were significantly lower in the seriously degraded meadow compared with the other degradation phases (P < 0.01). The Sorenson and Morisita-Horn similarity indices in the different degradation stages indicated that degradation of the alpine meadow had a strong effect on the taxonomic composition and dominant group abundances of soil insect communities. Moreover, the seasonal dynamics in the density and diversity of soil insect communities also differed among the different degradation stages. Degradation of the alpine meadow also changed the spatio-temporal distributions of the dominant taxonomic groups of soil insect communities. Correlation analysis showed that the diversity indices of soil insect communities were negatively correlated to soil pH (P < 0.01) and were positively correlated to below-ground biomass and phosphorus contents (P < 0.01), while the community density was only negatively correlated to soil pH (P < 0.01). Our results indicated that degradation of the alpine meadow influenced the taxonomic composition and spatio-temporal distributions of the soil insect communities by altering plant communities and soil properties.