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

土壤动物是凋落物分解、养分转化过程的重要调节者,全球变化驱动的氮沉降与降雨变化通过改变其分解环境和土壤动物群落结构,进而影响凋落物分解进程。为了探究中小型土壤动物对凋落物分解的贡献受氮沉降和降雨变化的影响,本研究利用不同网孔(2 mm和0.01 mm)的凋落物分解网袋法,以建群种短花针茅为研究对象进行野外分解试验。试验采用裂区设计,主区为自然降雨(CK)、增雨30%(W)和减雨30%(R)3个水分处理,副区为0(N₀)、30(N₃₀)、50(N₅₀)和100(N₁₀₀) kg·hm^-2·a^-1 4个氮素处理。结果表明: 1)降雨变化显著影响了凋落物的分解速率,增雨处理中凋落物的分解速率加快,且随着氮添加浓度的升高,凋落物重量残留率逐渐降低,100 kg·hm^-2·a^-1时分解速度最快;在减雨处理与对自然降雨处理中凋落物的分解速率则呈先降低后升高的趋势,在50 kg·hm^-2·a^-1时分解速度最快。氮沉降和降雨变化对凋落物分解无显著的交互作用。2)在整个分解过程中,共捕获中小型土壤动物1577只,隶属于1门3纲13目(含亚目)49科,优势类群为蜱螨目、鞘翅目幼虫和弹尾目;增雨施氮提升了中小型土壤动物群落的类群数和个体数。3)凋落物重量残留率与中小型土壤动物类群数、个体数均呈极显著负相关,增雨处理整体提高了中小型土壤动物对凋落物分解的贡献率。综上,荒漠草原上中小型土壤动物对凋落物的分解具有积极作用,且水分和氮素输入的增加提高了中小型土壤动物的类群数及个体数,增加了其对凋落物分解的贡献;在水分不足时,过量的氮素会抑制中小型土壤动物群落的发展,导致中小型土壤动物对凋落物分解的贡献降低。

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.