内蒙古温带典型草原植物凋落物和根系的分解及养分动态的研究

Decomposition and nutrients dynamics of plant litter and roots in Inner Mongolia steppe

在中国科学院内蒙古草原生态系统定位研究站,利用不同放牧强度下连续放牧了10年(1990-1999)的放牧样地,对停牧后草地恢复过程中的羊草(Leymuschinensis)、糙隐子草(Cleistogenessquarrosa)和星毛委陵菜(Potentillaacaulis)的凋落物和根系的分解及养分释放特性进行了研究。结果表明,植物凋落物和根系的分解及养分释放速率均以建群种羊草最高,重度退化种星毛委陵菜最低;凋落物和根系的分解及养分释放速率与木质素含量、C∶N、木质素∶N和木质素∶P均呈显著的负相关关系,而与土壤温度和土壤湿度则呈显著的正相关关系;在凋落物和根系的分解及养分释放过程中,土壤温度与土壤湿度存在极显著的互作效应。

∶Plant litter decomposition is a fundamental process of ecosystem functioning because it is a major determinant of nutrient cycling. The rate of plant decomposition and nutrient release varies with a number of factors, including the nature of the plant material. In general, low-nutrient species produce litter that is more difficult to decompose than litter from high-nutrient species. In arid and semiarid grasslands late-seral dominant grasses tend to have high tissue N concentrations and low C∶N ratios and lignin concentrations, which result in fast decomposition and nutrient mineralization. In this system, high-nutrient grasses are palatable to ungulate grazers, whereas low-nutrient grasses are unpalatable to ungulate grazers. In order to prove these hypothesis, a field experiment was conducted in the typical steppe area of central Inner Mongolia to test the characteristics of decomposition and nutrient release from leaf litter and roots from Leymus chinensis (high-nutrient, palatable grass), Cleistogenes squarrosa (middle-nutrient,palatable grass) and Potentilla acaulis (low-nutrient, unpalatable grass). Leaf litter and roots of each species were incubated in 3 mm mesh bags for 12 months at their source sites. Leaf litter decomposition was faster (P<0.01) in the palatable than in the unpalatable species and, on average, root decomposition was faster (P<0.01) in Leymus chinensis than in Cleistogenes squarrosa and Potentilla acaulis. At the end of the incubation period nitrogen (N) and phosphorus (P) release from the leaf litter and roots was higher (P<0.01) in the palatable than in the unpalatable species. The results on leaf litter and roots support the hypothesis that decomposition and nutrient release are faster in the palatable than in the unpalatable grasses. Moreover, decomposition of and nutrients release from plant litter and roots have significantly positive correlations with soil temperature and moisture, and significantly negative correlations with lignin content, C∶N ratio, Lignin∶N ratio and Lignin∶P ratio.