季节性冻融期间土壤动物对高山草甸两种凋落叶失重的贡献

季节性冻融期间高山草甸凋落叶的分解可为生长季节植物生长提供必要的养分,对于维持生态系统物质循环和养分平衡具有重要作用。然而,土壤动物对凋落叶分解是否具有明显的贡献仍然缺乏一致认识。因此,以高山草甸代表性植物黄花亚菊(Ajania nubigena)和黑褐苔草(Carex atrofusca)凋落叶为研究对象,采用不同孔径凋落叶袋排除土壤动物的方法,研究冬季不同冻融时期(冻结前期、冻结期和融化期)土壤动物对凋落叶失重的贡献。整个季节性冻融期间土壤动物对黄花亚菊和黑褐苔草两种凋落叶失重率的作用分别为12.07%和4.03%,总贡献率分别为46.39%和24.14%。土壤动物对两种凋落叶失重率的作用均在融化期最大,而土壤动物对黄花亚菊凋落叶失重率的作用在冻结初期最小,土壤动物对黑褐苔草凋落叶失重率的作用在冻结期最小。整个季节性冻融期,土壤动物对凋落叶失重率的作用和贡献率与正积温和凋落叶初始C、N浓度和C/N比均呈显著的正相关关系。因此,季节性冻融期间土壤动物对高山草甸凋落叶分解具有明显的贡献,但这些过程受冻融格局和凋落叶初始质量的调控。

Contribution of soil fauna to the decomposition of foliar litter of two alpine meadow plants during the season with freeze-thaw cycles

Foliar litter decomposition during the season with freeze-thaw cycles helps to replenish the store of nutrients necessary for ecosystem productivity for the subsequent growing season in alpine meadow ecosystems, and as such is an important process for the maintenance of materials cycling and nutrient balance in alpine meadows. However, little information is currently available about what effect soil fauna may have on foliar litter decomposition in cold-biome alpine meadow ecosystems, given that the severity of the environment during the season with freeze-thaw cycles might restrict soil fauna activity. To examine the possible influence of soil fauna, we conducted a field experiment in an alpine meadow in southwestern Sichuan, China, using litterbags of different mesh sizes to exclude or include soil fauna. The contribution of soil fauna to the foliar litter mass loss of two common plants, Ajania nubigena and Carex atrofusca, was examined during three distinct periods:the pre-freeze period, the freeze period, and the thaw period. Over the entirety of the season with freeze-thaw cycles, A. nubigena and C. atrofusca foliar litters lost 26.09% and 16.35% of their initial mass, respectively, in large-mesh litterbags, but lost only 14.02% and 12.31% of their initial mass, respectively, in small-mesh litterbags. However, the contribution of soil fauna to the foliar litter mass loss of two common plants, A. nubigena and C. atrofusca,were 46.39% and 25.14%, respectively, and the mass loss rates driven by soil fauna were 12.07% and 4.03%, respectively, during the season with freeze-thaw cycles. Compared with other periods, rates of foliar litter mass loss driven by soil fauna were highest in the thaw period for both A. nubigena and C. atrofusca. On the other hand, the lowest rates of mass loss driven by soil fauna occurred in the pre-freeze period for A. nubigena foliar litter but during the freeze period for C. atrofusca foliar litter. Moreover, it is notable that soil fauna negatively affected foliar litter mass loss in the pre-freeze period but positively impacted foliar litter in both the freeze and thaw periods. In addition, the rate of mass loss attributable to soil fauna was significantly (P<0.05) correlated with temperature and initial foliar litter quality, such as initial carbon (C) and nitrogen (N) concentrations and the C/N ratio during the season with freeze-thaw cycles. Loss of foliar litter mass was also significantly (P<0.05) influenced by the interactions between litterbag mesh size and litter decomposition period. Soil fauna also seemed to play a more active role in A. nubigena foliar litter decomposition than in C. atrofusca foliar litter decomposition. These results indicated that although soil fauna play a large role in the decomposition of foliar litter during the season with freeze-thaw cycles in alpine meadow ecosystems, this process is modulated by the dynamics of the freeze-thaw cycle and the initial quality of the foliar litter. A shorter period of snow cover or reduction in snow depth resulting from climate change could affect soil fauna activity and thus the rates of foliar litter decomposition in these alpine environments.