[Effects of soil meso- and micro-fauna on litter decomposition under nitrogen deposition and rainfall changes]

Soil fauna are important regulators of litter decomposition and nutrient transformation. Nitrogen deposition and rainfall changes driven by global changes could affect litter decomposition by changing environment and soil faunal community. Different mesh size (2 mm and 0.01 mm) litter bags were used to explore how soil meso- and micro-fauna contribute to decomposition of Stipa breviflora litter under nitrogen deposition and rainfall changes. The experiment followed split-plot design, with rainfall change (natural rainfall, CK; rainfall addition 30%, W; rainfall reduction 30%, R) as the main trement and nitrogen addition (0, N₀; 30, N₃₀; 50, N₅₀; 100 kg·hm^-2·a^-1, N₁₀₀) as the sub-treatment. The results showed that: 1) Rainfall change significantly affected litter decomposition rate, which was increased by rainfall addition. Moreover, litter decomposition rate was accelerated with increasing nitrogen addition rates. Litter residual rate decreased gradually with increasing N addition, and got to the highest in N₁₀₀. Litter decomposition rate decreased first and then increased, and peaked in N₅₀ in rain reduction and natural rainfall treatment. There was no significant interactions between rainfall change and nitrogen addition in affecting litter decomposition. 2) During the whole decomposition process, a total of 1577 soil meso- and micro-fauna were captured, belonged to 1 phyla, 3 classes, 13 orders (including suborders) and 49 families. The dominant groups were Acarina, Coleoptera larvae, and Collembola. Nitrogen addition significantly increased abundance and group numbers of soil meso- and micro-fauna. 3) The litter mass residue rate was significantly negatively correlated with abundance and group numbers of soil meso- and micro-fauna. The contribution rate of soil meso- and micro-fauna to litter decomposition increased with increasing rainfall. In summary, soil meso- and micro-fauna had a positive effect on decomposition of Stipa breviflora litter in desert steppe. Their contribution to litter was promoted by the enhancement of soil mesofauna abundance and group under rainfall and nitrogen addition. Excessive nitrogen would inhibit soil meso- and micro-fauna community and group density when water was insufficient, and would thus weaken the function of soil mesofauna to litter decomposition.