森林凋落物分解重要影响因子及其研究进展

当前 ,森林凋落物分解被放在陆地生态系统碳平衡背景下进行研究 ,认识凋落物分解过程的影响因素和影响机理对理解地表碳平衡具有重要意义。凋落物在分解过程中 ,伴随有养分含量的变化 ,低品质凋落物在分解前期 (可达 2～ 3年 )会从环境中固定养分 ,特别是氮磷养分 ,而在后期则会释放出养分。凋落物本身的养分含量是影响分解速率的重要因素 ,高养分含量的凋落物分解快些 ,阔叶凋落物比针叶凋落物分解快些。有资料显示 ,在总分解率为2 9 4 %的构成中 ,理化因素、微生物因素与土壤动物因素对凋落物分解的贡献率分别为 7 2 %、8 0 %和 14 2 %。不同类型凋落物在分解过程中的土壤动物类群也不同 ,它也是造成凋落物分解速率不同的关键因素 ,通常阔叶树种凋落物分解过程中 ,会有更多的微节肢动物出现。CO2浓度升高将造成植物有机质含碳量与其它养分的比值升高 ,形成低品质的凋落物 ,从而间接影响凋落物分解速率 ,一般认为 ,全球CO2 浓度升高会加强土壤作为碳汇的功能。

Key factors of forest litter decomposition and research progress

This paper reviews the research advance in litter decomposition of forest ecosystem,with special attention to nutrient processes and the factors regulating the decomposition.Traditionally,litter decomposition has been studied on the background of nutrient cycle in forest ecosystem.But modern work is associated with the carbon balance of terrestrial ecosystem on the background of global change.Lots of documents have addressed such factors regulating the decomposition as litter quality,biological contribution and physical factors.Nutrient release from the litter is related to the stage of decomposition.About 2 years or 50% of decay are often the time when litter begins to release nutrients for many litter types,while during the initial period,decomposition often results in immobilization of nutrient from the environment.This occurs mainly for N and P,but not for metal elements.Litter quality is the key factor governing the nutrient release,with which C/N ratio is highly correlated.Litter quality is also a key factor determining the decomposition rate.Litter of high nutrient content (especially of N and P) decomposes fast.This quality controlled process mainly happens in the initial stage of decomposition.Some organic components such as lignin and cellulose in litter are also important factors governing the decomposition.Lignin/N,lignin/P and other ratios of recalcitrant substance to inorganic nutrient are widely used indicators of litter decomposability.Biological and physical-chemical factors contribute to the litter decomposition.Reference data of contribution are 7.2% (only physical-chemical),8% (only microbiological) and 14.2% (only soil animals) in a total decomposition of 29 4%.Litter quality results in the difference of soil fauna and microbes,which in return influences the decomposition rate.Abundance of soil fauna and microbes as a result of better quality of broadleaf litter accounts for the accelerated decomposition of pine needles when they are mixed together.Rise of CO 2 concentration in the atmosphere enhances the primary productivity of forest ecosystem,but the quality of litter decrease,as a result,with higher C/N.Lower quality litter decomposes more slowly.High CO 2 seems no direct impact on the decomposition.In general,high CO 2 as a consequence of global change is expected to strengthen the role of soil as a sink of carbon.However,more investigation is needed in this context.