[Effects of soil meso- and micro-fauna on litter decomposition under nitrogen deposition and rainfall changes]. / 氮沉降与降雨变化下中小型土壤动物对凋落物分解的影响.

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.

Effects of exogenous nitrogen input and water change on litter decomposition in a desert grassland.

Under the background of global climate change, atmospheric nitrogen deposition and precipitation are undergoing substantial changes, which leads to an uncertainty on litter decomposition in desert grassland. The experiment was set up with a split-plot design. There were three precipi-tation treatments, including natural precipitation, an increase of 30% and a decrease of 30%, and four levels of nitrogen application, including 0 (N0), 30 (N30), 50 (N50) and 100 kg·hm-2·a-1 (N100). A two-year decomposition experiment aimed to examine how water and nitrogen manipulations interactively influence litter decomposition of three dominant species in the desert grassland, i.e., Salsola collina, Stipa breviflora and Kochia prostrata. The results showed that litter mass remaining rate decreased with time, which was consistent with Olson negative exponential decay model. Litter decomposition coefficient (k) was highest for S. collina, followed by S. breviflora and K. prostrata. The decomposition coefficient (k=0.028) was the highest under the treatment of increased precipitation 30% and N application level of 100 kg·hm-2·a-1. Under single factor treatment, litter decomposition was the fastest under increased precipitation 30% and N application level of 50 kg·hm-2·a-1. Under the combined water and nitrogen treatments, litter decomposition under increased precipitation 30% and N application level of 100 kg·hm-2·a-1 was the fastest. The initial nitrogen content was the greatest for S. collina, followed by S. breviflora and K. prostrata. The decomposition coefficients were positively correlated with initial nitrogen contents for S. collina and S. breviflora. The total carbon content, cellulose content, lignin content, C/N, lignin/N and cellulose/N were higher in K. prostrata than in S. breviflora and S. collina. The litter characteristics were negatively correlated with decomposition coefficient for S. collina. For S. breviflora and K. prostrata, the decomposition coefficients decreased with increasing C/N, lignin/N and cellulose/N. The results indicated that the decomposition rate was the highest in S. collina, and the lowest in K. prostrata. The findings suggest that appropriate amounts of added water and nitrogen will contribute to accelerating litter decomposition, promoting nutrient cycling, and will play an important role in the sustainability and ecological balance of the desert grassland .