Abstract:

Soil microarthropod communities are an important component of grassland ecosystems and community structures are highly sensitive to environmental changes. This study aimed to characterize the changes in soil microarthropod communities associated with alpine grassland degradation and to make tentative deductions on the roles of microarthropods in the process of degradation. Four alpine grasslands in Northwest Sichuan， comprising a degradation series including non-degraded， lightly degraded， moderately degraded and severely degraded grasslands， were selected for study and the soil microarthropod communities within the 0-20 cm soil layer were investigated in July 2019 and July 2020. Soil microarthropods were extracted from the soil samples for 48 h at 38 ℃ using the Tullgren method in the laboratory. It was found that： 1） The taxonomic composition and dominant taxonomic groups of soil microarthropod communities differed among the four different degradation stages. With increasing degradation， the density， number of taxonomic groups and Shannon diversity index of soil microarthropod communities initially increased then decreased （P<0.01）， while Simpson index initially decreased then increased （P<0.01）. 2） Different groups of soil microarthropods responded variously to degradation. The abundance of mites decreased steadily with each increase in alpine grassland degradation （P<0.01）， while the abundance of Collembola increased from non-degraded to moderately grassland but was decreased in severely degraded grasslands （P<0.01）. 3） The density and diversity of soil microarthropods were significantly correlated with soil environmental factors such as soil organic carbon， humidity， total N， pH， C/N ratio， height and species number of plant communities （P<0.001， 0.01 or 0.05）. The mite abundance differed significantly with differences in soil bulk density， soil organic carbon， total N， C/N ratio and pH （P<0.001， 0.01 or 0.05）， but none of these factors was significantly linked to change in the Collembola abundance （P>0.05）. The results indicate that the degradation of alpine grasslands affects the taxonomic composition， density and diversity of soil microarthropod communities mainly through soil environmental factors， and the abundance of mites can be used to monitor the degree of degradation of alpine grasslands.

Key words: soil microarthropod, alpine grassland, degradation, Northwest Sichuan