陆地生态系统混合凋落物分解研究进展

凋落物分解在陆地生态系统养分循环与能量流动中具有重要作用,是碳、氮及其他重要矿质养分在生态系统生命组分间循环与平衡的核心生态过程。自然生态系统中,植物群落大多具有较高的物种丰富度和多样性,其混合凋落物在分解过程中也更有可能发生养分传递、化学抑制等种间互作,形成多样化的分解生境,多样性较高的分解者类群以及复杂的级联效应分解,这些因素和过程均对研究混合凋落物分解过程、揭示其内在机制形成了极大的挑战。从构成混合凋落物物种丰富度和多样性对分解生境、分解者多样性及其营养级联效应的影响等方面,综合阐述混合凋落物对陆地生态系统凋落物分解的影响,探讨生物多样性在凋落物分解中的作用。通过综述近些年的研究发现,有超过60%的混合凋落物对其分解速率的影响存在正向或负向的效应。养分含量有差异的凋落物混合分解过程中,分解者优先利用高质量凋落物,使低质量的凋落物反而具有了较高的养分有效性,引起低质量凋落物分解加快并最终使混合凋落物整体分解速率加快;而凋落物物种丰富度对土壤动物群落总多度有轻微的影响或几乎没有影响,但是对线虫和大型土壤动物的群落组成和多样性有显著影响,并随着分解阶段呈现一定动态变化;混合凋落物改变土壤微生物生存的理化环境,为微生物提供更多丰富的分解底物和养分,优化微生物种群数量和群落结构及其分泌酶的活性,并进一步促进了混合凋落物的分解。这些基于植物-土壤-分解者系统的动态分解过程的研究,表明混合凋落物分解作用不只是经由凋落物自身质量的改变,更会通过逐级影响分解者多样性水平而进一步改变分解速率和养分释放动态,说明生物多样性确实在一定程度上调控凋落物分解及其养分释放过程。

The research of mixed litter effects on litter decomposition in terrestrial ecosystems

Decomposition is one of the most important ecosystem processes, which plays a critical role in regulating nutrient cycling and energy flow in terrestrial ecosystems. In terrestrial ecosystems, multiple plant species coexist in a community with high plant species richness, which may lead to diverse plant litter input and complicated litter chemicals, high microhabitat heterogeneity, and highly diverse decomposers and their interactions. Mixed soil litters with diverse plant species usually have more complex mechanism underlying decomposition because of the complementary use of nutrients and transfer among different species, greatly challenging the assumptions about litter decomposition and biodiversity. We reviewed the studies on decomposition of mixed-species litter in terms of the impact of plant diversity on litter quality, decomposing microhabitats, and decomposers and their interactions. We found that the majority of recent studies revealed a non-additive effect of mixed litters on mass loss and nutrient dynamics during the duration of decomposition. The occurrence of some specific plant species might strengthen the non-additive effect because they contained some special compounds. Different litter types differ in chemical composition and physical properties, and decomposing of high-quality litter by decomposer organisms eventually leads to a high nutrient availability and allows nutrient transfer to low-quality litter. Transferred nutrients, in turn, lead to a more rapid decomposition of the low-quality litter and, consequently, of the entire litter mixture. Litter species identity was an important determinant of abundance and diversity of soil fauna, while litter mixing had weak or no significant effect on the soil fauna communities; however, it had significant effect on components of the macrofauna and nematodes and their diversity. Moreover, the effects of mixed litters on decomposers usually depend on the decomposing time. Some studies showed that litter diversity may induce significant changes in the composition, diversity, and enzyme activities of decomposers such as soil fauna and microbes, and also modify the interactions among the decomposers, which may induce further changes in litter decomposition. These results suggest significant effects of mixed litter on decomposition rate and an important role of decomposers in regulating decomposition of mixed litters, which are helpful to understand the effects of mixed litter on litter decomposition and nutrient dynamics in the plant-soil-decomposer system.