森林凋落物分解研究进展

Review on litter decomposition in forest ecosystems

森林凋落物分解是森林生态系统养分生物循环的重要环节,而分解过程中所释放的CO2是全球碳素收支的重要组分,开展森林凋落物分解研究是充分认识森林生态系统结构和功能的基础。研究认为:凋落物分解的预测指标可分为3类,即环境指标(如实际蒸散量)、凋落物物理质量(如叶抗张强度)和化学质量指标(如C/N比、木质素/N比和C/P比等);凋落物分解过程中养分释放机制极其复杂,养分动态模式主要有淋溶—释放、淋溶—富集—释放和富集—释放3种,并因凋落物种类、分解阶段和元素本身性质的不同而异;凋落物混合分解并非单一树种分解的简单叠加,因树种组成和比例不同,基质的化学组成会发生变化,从而影响分解者的多样性、丰富度和生理活性,进而直接和间接地影响其分解速率;凋落物混合分解中可能存在无效应、促进效应和抑制效应;现有的研究结果显示,凋落物混合分解的适宜比例应与群落中不同树种的种群比例相一致;CO2浓度升高不仅影响凋落物的化学性质,而且与分解环境中土壤的生物活性密切相关,但CO2浓度升高并不改变凋落物质量与分解速率之间的关系;越来越多的研究显示,CO2浓度升高的环境下,植物群落的物种组成会产生变化,这种变化对养分循环速率的影响远大于单纯大气CO2浓度变化的影响。

Abstract Litter decomposition and related nutrient release are fundamental process of nutrient est ecosystems, and an important component of global carbon budget. A thorough understanding cycling in forof decomposition process is essential in understanding the structure and functioning of forest ecosystems. Decomposition predictors can be divided into three types, including environmental index （e. g. actual evapotranspiration （AET））, litter physical and chemical quality indices （e. g. leaf tensile strength （LTS）, C/N, lignin/N and C/P ratios etc. ）. The mechanism of nutrient release in decomposition is extremely complicated. There are three types of dynamical patterns of nutrients during the decomposition process such as leaching-release, leaching-accumulation-release, and accumulation-release, which vary with litter types, decomposition phases, and elements with respect to both the mobility of nutrients and limitations of nutrients on decomposer organisms. The decomposition of mixed-species litter exhibits different responses such as synergistic, antagonistic or null response, depending largely on species composition and the proportion of individual litter types. Mixtures of different litters likely result in both chemical diversity and microhabitat complexity, which correlated with the change in abundance and physiological activities of the decomposers. Emerging researches suggested that in the mixed-litter experiment, the representation of litter types in proportions should determined by those in the natural setting. Elevated CO2 can affect the litter chemistry and biotic and abiotic environment including soilresource availability, soil fauna community and the activity of soil enzymes responsible for the decomposition of litter. However, elevated CO2 do not alter the relationship between litter chemistry and decomposition. The resuhs from most emerging under elevated CO2 have a spheric CO2 alone. researches implied that changes in the species composition of the plant community much larger effect on the long-term rate of nutrient cycling than changes in atmospheric CO2 alone.