贵州喀斯特山区不同植被下土壤C、N、P含量和空间异质性

西南喀斯特地区是中国四大生态脆弱地区之一,为了解喀斯特生态环境下植被演替对土壤养分循环的影响,选取贵州中部喀斯特地区由乔木林、灌木林和灌草丛等不同植被类型下的土壤为研究对象,采用样块法采集了表层土壤样品,测定C、N、P全量及有效态含量,分析了这些元素的空间异质性特点.结果表明,各养分元素无论全量和有效态含量均在乔木林下最高,灌木林下有机碳及N、P全量的下降并不显著,但养分有效态含量显著下降,而灌草丛下土壤养分无论是全量还是有效态含量均较灌木林下显著降低下降;土壤养分空间异质性在灌木林下最高,土壤全磷素特别是速效磷的空间异质性高于有机碳和N.这显示,不仅是土壤养分含量,而且土壤养分的空间异质性都随植被演替而改变.这种变化中,土壤养分有效态较全量更为剧烈.植物类型和结构变化下凋落物返还及土壤生物化学转化环节的变化可能是引起喀斯特生态系统退化下土壤养分库降低而空间异质化提高的主要原因,这最终也会影响土壤养分在生态系统内的循环和分布.

Changes in pools and heterogeneity of soil organic carbon, nitrogen and phosphorus under different vegetation types in Karst mountainous area of central Guizhou Province, China

The karst areas of Southwest China had been considered as one of four ecotones in China. To understand the impacts of the succession of vegetation on soil nutrient pool and the heterogeneity in the karst ecosystems, quadram sampling of topsoil was done and pools (total and available contents) and the spatial distribution were analysed under three different vegetation types (forest, shrubs and grassland) in karst mountainous area from central Guizhou province,China. The results showed that, both total and vailable pool of OC, N and P was highest under forest and decreased under shrub and grasslands, with the more prominent descending trend for available pools. However, highest satial heterogeneity of nutrient pools was found under schrub and associated with soil P. This indicated changes both in total pool and in spatial distribution with vegetation degrdation in the karst area. Nutrient availability was shown in prompt response to vegetation degradation. Changs in littering and the associated soil biochemical transfromation may occur under vegetation degradation which, in turn, may result in reduction of nutrient pool and increase in spatial variability. These changes in soil nutrient status may ultimastely impact on ecosystem cycling of life elements and the productivity in the long run.