祁连山典型流域谷地植被斑块演变与土壤性状

植物群落演变与土壤性状变化之间的相互作用和过程研究对于认识生态系统结构和功能演变有着重要的意义.对祁连山谷地灌丛草甸退化演变过程中植物群落物种组成、土壤物理和化学性状特征、及土壤与植被的相互作用进行了研究,结果表明,在祁连山谷地阴坡林线以下较小的空间范围,植被斑块由金露梅群落向金露梅-马蔺群落斑块和马蔺群落斑块演变,植被盖度降低,但物种多样性增加.不同植被斑块之间土壤水分有显著的梯度变化,土壤水分的变化导致植被的退化演替.植被斑块的演变导致土壤性状的明显分异,从金露梅灌丛斑块向金露梅-马蔺群落斑块和马蔺群落斑块演变,土壤容重显著增加,土壤团聚体组成由大粒级的大团聚体(》1mm)破碎为小粒级的大团聚体(1-0.25mm)和微团聚体(《0.25mm),团聚体稳定性降低,表明土壤结构的退化;土壤有机碳含量下降了31.2%和55.9%,干筛各粒级土壤团聚体中有机碳含量金露梅-马蔺群落斑块和马蔺群落斑块显著低于金露梅斑块,土壤团聚体平均重量粒径与有机碳含量存在显著相关,植被退化演变中土壤有机碳的损失部分地由于团聚体的破碎引起;土壤全氮和有效氮不同斑块之间也有显著的差异,植被斑块退化演变使氮的有效性降低;但磷、钾养分对植被变化的响应不敏感.植被的退化演变使土壤团聚体破碎、土壤结构退化,有机碳和全氮含量下降,使其抗侵蚀能力和水源涵养功能显著降低,又进一步加速植被的退化演替.在气候变暖的趋势下,马蔺斑块将进一步向林线逼近,灌丛草甸植被将会进一步退化和萎缩.

Changes in vegetative patches and characteristics in soil properties in the valleys of Qilian Mountains

Research on interaction and processes between plant community succession and soil property changes has significant implications for understanding evolution of ecosystem structure and function. In this paper, plant species composition, characteristics in soil physical and chemical properties and vegetation-soil interactions in the degraded succession stage of shrub meadow community were investigated in the valleys of Qilian Mountains. Within a small spatial scale in the edge of forest in the valley of southern of mountains, plant community patch evolved from Potentilla fruticosa community to Potentilla fruticosa- Iris lacteal patch, and further to Iris lacteal community patch. The vegetative coverage decreased, but the species diversity increased. There was an evident gradient change in soil water content among different vegetative patches, showing that soil water availability resulted in the succession in vegetative community patches. The evolution of vegetative patch has a strong influence on soil physical and chemical properties. From Potentilla fruticosa patch to Iris lacteal patch, soil bulk density significantly increased, the proportion of larger macro-aggregate fractions (>1mm) decreased and that of small macro-aggregate (1-0.25mm) and micro-aggregate fractions (<0.25mm) increased, and aggregate stability decreased, suggesting that soil structure degraded. Soil organic carbon concentration (SOC) decreased by 31. 2% and 55.9% in Potentilla fruticosa-Iris lacteal patch and Iris lacteal patch, respectively, compared with Potentilla fruticosa patch. Also, OC concentration in dry-sieved aggregate classes was higher in the Potentilla fruticosa patch than in the other two patches. There is a close linear relationship between SOC and mean weight diameter of dry-sieved aggregates (DMWD). Loss of SOC in the degraded succession of vegetation is partly due to the breakdown of macro-aggregates. Total and available nitrogen concentrations decreased significantly from Potentilla fruticosa patch to Iris lacteal patch, but the decreased extent is less than that of SOC, resulting in a decreased C/N in Iris lacteal patch. However, the differences in total and available phosphorus and potassium nutrients among different vegetative patches were not observed. The degradation of soil structure due to macro-aggregate breakdown and the decline in SOC and nitrogen availability resulted in the decrease in resistance to erosion and in the function of water and soil conservation, and in turn, further accelerate degraded succession of vegetation. Under the drive of drought due to global climate warming, Iris lacteal community patch may further develop towards forest line and shrub meadow vegetation may further degrade and shrink.