内蒙古草原凋落物分解对生物多样性变化的响应

Responses of litter decomposition to biodiversity manipulation in the Inner Mongolia grassland of China

生物多样性与生态系统功能紧密相关。凋落物分解作为生态系统重要功能之一,对植物群落的物种组成和多样性具有反馈作用。本研究在内蒙古草原通过功能群去除产生不同的多样性梯度,应用分解网袋法,研究了草原生态系统的生物多样性变化对凋落物分解过程的影响。实验分为相互补充的三个部分,(1)分解微生境实验:研究了由于功能群多样性改变引起的分解微生境变化对凋落物分解的影响;(2)凋落物组成实验:研究了4个功能群的优势物种羊草(Leymus chinensis)、大针茅(Stipa grandis)、细叶葱(Allium tenuissimum)、刺穗藜(Chenopodium aristatum)的单种及不同组合的混合凋落物在相同的分解微生境下物种间的相互作用对凋落物分解过程的影响;(3)综合分解微生境和凋落物组成两种影响因素,将收集的凋落物的单种及其混合物放回原样方进行分解。结果表明,功能群多样性高的样方中,其微生境有利于凋落物的分解;混合凋落物的分解具有非加和性效应。混合凋落物的分解速率与其初始碳含量呈负相关,与其初始氮、磷含量呈正相关;当混合凋落物在功能群多样性不同的微生境中分解时,重量降解速率与微生境中的功能群多样性没有显著的相关关系,氮流失与功能群多样性呈正相关。我们的研究表明,群落中凋落物组成和凋落物的功能群多样性相比,前者是影响凋落物分解的决定性因素;与地上存活植株所参与的生物学过程相比,凋落物分解受生物多样性的影响较小;在生物多样性更高的区域,氮的循环加速,有利于提高群落的生产力。

Litter decomposition as one of the important ecosystem functions has strong interactions with ecosystem biodiversity. This is because recycling of nutrients during litter decomposition has major control over the carbon cycle and nutrient availability. Therefore, decomposition is crucial to qualify diversity effects on ecosystem processes. Here, we conducted a litterbag experiment in temperate grassland of Inner Mongolia, China, to examine the effects of altering plant functional group diversity on litter decomposition. We performed three related decomposition experiments within the Inner Mongolia Grassland Removal Experi- ment （IMGRE）, which was established with a manipulated gradient of functional group diversity. （1） The first experiment is a microenvironment experiment, furca were used to examine the decomposition rates in which litters of Kochia prostrata and Potentilla biof different functional group assemblages. （2） The second experiment is litter quality experiment, which included four species, Leymus chinensis, Stipa grandis, Allium tenuissimum, and Chenopodium aristatum. Different litter combinations of the four species were placed in a homogeneous environment to test the effects of litter composition on the decomposition. （3） The third experiment was a combination of the above two experiments. The single or a combination of plant litter from species rich plots was placed back to its original plots. Our results showed that decomposition rates of both Kochia prostrata and Potentilla bifurca litter increased with the number of functional groups in the decom- posing environment in the first experiment. Non-additive patterns of mass loss were observed in the second experiment. A significant negative correlation between carbon content of the litter mixtures and litter mass loss rate, and positive correlations between nitrogen, phosphorus concentrations and litter mass loss rates were observed. When decomposition microenvironment and litter composition were assessed simutanously, no significant correlations were observed between decomposition rates and the number of functional groups or species diversity. However, a positive correlation was found between nitrogen loss and functional groups. Thus, we concluded that litter diversity itself had smaller effects than species identity, and decomposition was less sensitive to changes in plant diversity compared with other ecosystem processes which depend more on vitality of plants. Furthermore, our results have the implication that higher plant species richness allows vegetation to exploit soil resources more efficiently.