Effect of water table decline on the abundances of soil mites, springtails, and nematodes in the Zoige peatland of eastern Tibetan Plateau

Despite the important role of soil fauna in the decomposition of soil organic matter, the abundance response of soil fauna to environmental changes has been scarcely studied in peatlands, where soil carbon content is exceptionally high. The water table of the Zoige peatland, the largest alpine peatland worldwide, has been declining due to climate change and human drainage in recent decades, which likely induces changes in the abundance of soil fauna. In order to examine the abundance response of soil mites, springtails, and nematodes to water table decline in the Zoige peatland, we conducted an in situ field drainage experiment, consisting of low, intermediate, and ambient water table levels for four consecutive years. We measured the abundances of mites, springtails, and nematodes at five soil depths (0-5, 5-10, 10-15, 15-20, and 20-25 cm), for four times in the third and fourth year of the experiment. Results show that the effect of water table decline on the abundance of soil fauna varied among soil animal groups, soil depths, and the sampling times over the course of the experiment. While mites did not respond significantly to the experimental treatments, the abundance of springtails at soil depths of 0-5, 5-10, and 10-15 cm and that of nematodes at a depth of 15-20 cm were significantly higher in the drained treatments than in the undrained one. Moreover, water table decline increased the proportion of herbivorous nematodes in the top soil (0-5 cm) and decreased the proportion of bacterivorous nematodes at soil depths of 0-5 and 5-10 cm, while fungivorous and omnivorous-predaceous nematodes did not respond significantly. Given the demonstrated importance of soil fauna to soil carbon dynamics, the changes in the abundances of soil mites, springtails, and nematodes depicted here indicate that soil fauna should be further studied in relation to the recently reported rapid loss of soil carbon in the Zoige peatland.