尕海湿地植被退化过程中土壤轻重组有机碳动态变化特征

以甘肃省甘南尕海湿地内的沼泽化草甸为研究对象,采用野外取样和室内测试相结合的方法,研究植被退化过程中土壤轻重组有机碳含量及动态变化。结果表明:不同植被退化阶段0—20cm土壤轻组有机碳含量差异显著(P0.05),表现为未退化轻度退化重度退化中度退化;20—100cm土壤轻组有机碳受植被影响较小。整个土壤剖面重组有机碳含量表现为中度和重度退化显著高于未退化和轻度退化(P0.05)。土壤轻重组有机碳含量均随土壤剖面下降显著降低(P0.05)。各退化阶段沼泽化草甸土壤轻重组有机碳均呈现出明显的时间变化,在0—20cm土层,未退化阶段轻组有机碳表现为"降—升—降"的变化趋势,即5月最高,7月和9月最低,其他各退化阶段则在6月降低并趋于稳定;20—100cm土层轻组有机碳变化幅度较小。各退化阶段土壤重组有机碳动态变化较为一致,均随时间延长呈线性下降,不同月份之间差异显著(P0.05)。说明植被退化导致轻组有机碳含量下降,重组有机碳增加,而在植被生长过程中主要消耗轻组有机碳,重组有机碳相对稳定。相关分析表明,地下生物量与土壤含水量的变化对土壤轻重组有机碳影响显著。

Dynamic Characteristics of Soil Light and Heavy Fraction Organic Carbon During Vegetation Degradation in Gahai Wetland

In order to study the contents and dynamic characteristics of soil light and heavy fraction organic carbon during the vegetation degradation process, the filed and laboratory experiments were conducted in marsh meadow of Gahai wetland in Gannan state, Gansu province. The main results were as follows:The soil light fraction organic carbon contents in 0-20 cm layers varied in different stages of vegetation degradation of marsh meadow, following the order of UD (undegraded) > LD (lightly degraded) > HD (heavily degraded) > MD (moderately degraded). The soil light fraction organic carbon in 20-100 cm layer was less effected by vegetation degradation. The soil heavy fraction organic carbon contents HD and MD stages of vegetation degradation were significant higher than UD and LD in entire soil layer (P<0.05). With the increasing soil layers, all the soil light and heavy fraction organic carbon contents significantly decreased. The soil light and heavy fraction organic carbon showed the obvious dynamic characteristics with time in all stages of vegetation degradation. The soil light fraction organic carbon contents gave a trend of "down-up-down" in UD stages of vegetation degradation in 0-20 cm soil layer, i.e., the highest in May, the lowest in July and September. But the contents were reduced and stabilized in June in the other stages of vegetation degradation. The variations of soil light fraction organic carbon contents was small in 20-100 cm soil layers. The variations of soil heavy fraction organic carbon contents were consistent in all stages, giving linear decreases with time, the significant difference occurred between different months (P<0.05). These findings indicated that vegetation degradation could result in the decreases of soil light fraction organic carbon, and the increases of heavy fraction organic carbon. However, the main consumption of soil organic carbon is the light fraction, and the heavy fraction is relatively stable. Correlation analysis showed that the changes of underground biomass and soil moisture contents had significant influence on soil light and heavy fraction organic carbon.