凋落物多样性及组成对凋落物分解和土壤微生物群落的影响

凋落物分解是生态系统营养物质循环的核心过程,而土壤微生物群落在凋落物分解过程中扮演着极其重要且不可替代的角色。随着生物多样性的丧失日益严峻,探讨凋落物多样性及组成对凋落物分解和土壤微生物群落的影响,不仅有助于了解凋落物分解的内在机制,而且可为退化草原生态系统的恢复提供参考。以内蒙古呼伦贝尔草原退化恢复群落中的草本植物为研究对象,依据植物多度、盖度、频度和物种的重要值及其在群落中的恢复程度筛选出排序前4的羊草（Leymus chinensis）、茵陈蒿（Artemisia capillaris）、麻花头（Serratula centauroides）、二裂委陵菜（Potentilla bifurca）的凋落物为实验材料,通过设置3种凋落物多样性水平（1,2,4）,包括11种凋落物组合（单物种凋落物共4种,两物种凋落物混合共6种,四物种凋落物混合共1种）,利用磷脂脂肪酸（PLFA）方法来研究分解60 d后凋落物多样性及组成对凋落物分解和土壤微生物群落的影响。结果表明：（1）凋落物物种多样性仅对C残余率具有显著影响,表现在两物种混合凋落物C残余率显著低于单物种凋落物,而凋落物组成对所观测的4个凋落物分解参数（质量、C、N残余率以及C/N）均具有显著影响;（2）凋落物物种多样性对细菌（B）含量具有显著影响,而凋落物组成对真菌（F）含量具有显著影响,两者对F/B以及微生物总量均无显著影响;（3）冗余分析结果表明凋落物组成与凋落物分解相关指标（凋落物质量、C、N残余率及C/N）和土壤微生物（真菌、细菌含量）的相关关系高于凋落物多样性。（4）进一步建立结构方程模型（Structural Equation Model,SEM）发现,凋落物初始C含量对凋落物质量、C、N残余率及C/N有显著正的直接影响;凋落物木质素含量对凋落物质量、C、N残余率有显著正的直接影响;凋落物初始N含量对N残余率有显著正的直接影响,而对C残余率及C/N有显著负的直接影响;凋落物初始C/N对凋落物质量、N残余率有显著正的直接影响,而对C/N有显著负的直接影响。此外,凋落物初始C、N、木质素含量及C/N均对真菌含量具有显著正影响,并可通过真菌对凋落物质量分解产生显著负的间接影响。以上结果表明该退化恢复区域优势种凋落物分解以初始C、木质素为主导,主要通过土壤真菌影响凋落物的分解进程,这将减缓凋落物的分解速率进而减慢草原生态系统的进程。这些结果为凋落物多样性及组成对自身分解和土壤微生物群落的影响提供了实验依据,也为进一步分析凋落物分解内在机制以及草原生态系统的恢复提供了数据参考。     

凋落物多样性及组成对凋落物分解及土壤微生物群落的影响——二氧化碳倍增条件下

受全球变化的影响生物多样性的丧失日益严重,及时了解凋落物物种多样性及其组成如何直接或者通过调节微生物群落来间接影响凋落物分解已经成为生态学领域的热点问题之一。在呼伦贝尔典型草原区,羊草（Leymus chinensis）为原生群落建群种,茵陈蒿（Artemisia capillaris）、麻花头（Serratula centauroides）、二裂委陵菜（Potentilla bifurca）在退化及恢复群落中的多度均较大,本研究以此4种植物的凋落物为研究对象,在两倍于当前大气CO₂浓度（800 μmol/mol）条件下,通过嵌套实验设计来研究凋落物多样性（凋落物组成）对凋落物质量、C、N残余率和残余C/N的影响,并深入分析凋落物初始性质以及土壤革兰氏阳性菌（G⁺）、革兰氏阴性菌（G^-）、细菌（B）、真菌（F）及土壤总微生物磷脂脂肪酸（Phospholipid Fatty Acid,PLFA）含量和F/B对凋落物分解的影响。结果表明：（1）凋落物多样性及组成对凋落物质量、C、N残余率以及残余C/N均具有显著影响;凋落物组成对G⁺ PLFAs含量具有显著影响;（2）冗余分析（Redundancy Analysis,RDA）结果表明凋落物组成对凋落物分解和土壤微生物群落相关指标的影响高于凋落物多样性;（3）结构方程模型（Structural Equation Model,SEM）结果表明凋落物初始木质素含量和初始C/N均对凋落物分解具有显著影响,其中凋落物初始木质素含量起主导作用,其还可通过对土壤真菌PLFAs含量的影响来间接影响凋落物N残余率和残余C/N。所得结果可为大气CO₂浓度升高条件下退化草原生态系统的物质循环特征的预测乃至草原生态系统功能的合理评估提供数据支持。     

Litter Decomposition and Nutrient Release in a Tropical Seasonal Rain Forest of Xishuangbanna,Southwest China1

We studied litter decomposition and nutrient release in a tropical seasonal rain forest of Xishuangbanna, Southwest China. The monthly decay rates (k) of leaf litter ranged from 0.02 to 0.21/mo, and correlated with rainfall and soil moisture. Annual k values for leaf litter (1.79/yr) averaged 4.2 times of those for coarse wood (2.5–3.5 cm in diameter). The turnover coefficients of forest floor mass (annual litterfall input/mean floor mass) were: 4.11/yr for flowers and fruits, 2.07/yr for leaves, and 1.17/yr for fine wood (≤2 cm in diameter), with resident time decreasing from fine woods (0.85 yr) to leaves (0.48 yr) and to flower and fruits (0.24 yr). Nutrient residence times in the forest floor mass were ranked as: Ca (1.0 yr) > P (0.92 yr) > Mg (0.64 yr) > N (0.36 yr) > K (0.31 yr). Our data suggest that rates of litter decomposition and nutrient release in the seasonal rain forest of Xishuangbanna are slower than those in typical lowland rain forests, but similar to those in tropical semideciduous forests.     

Does nitrogen availability control rates of litter decomposition in forests?

The effects of increased exogenous N availability on rates of litter decomposition were assessed in several field fertilization trials. In a jack pine (Pinus banksiana Lamb.) forest, needle litter decomposed at the same rate in control plots and in plots fertilized with urea and ammonium nitrate (1350 kg N ha^-1) with or without P and K. Mixed needle litter of western hemlock (Tsuga heterophylla (Raf.) Sarg.), western red cedar (Thuja plicata Donn) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) incubated in plots recently amended with sewage sludge (500 kg N ha^-1) lost less weight during 3 years than did litter in control plots. Forest floor material also decomposed more slowly in plots amended with sewage sludge. Paper birch (Betula papyrifera Marsh.) leaf litter placed on sewage sludge (1000 kg N ha^-1), pulp sludge, or sewage-pulp sludge mixtures decomposed at the same rate as leaf litter in control plots. These experiments demonstrate little effect of exogenous N availability on rates of litter decomposition.The influence of endogenous N availability on rates of litter decomposition was examined in a microcosm experiment. Lodgepole pine (Pinus contorta var. latifolia Engelm.) needle litter collected from N-fertilized trees (525 kg N ha^-1 in ammonium nitrate) were 5 times richer in N than needles from control trees (1.56% N versus 0.33% N in control trees), but decomposed at the same rate. Green needles from fertilized trees contained twice as much N as needles from control trees (1.91% N versus 0.88% N), but decomposed at the same rate. These experiments suggest that N availability alone, either exogenous or endogenous, does not control rates of litter decomposition. Increased N availability, through fertilization or deposition, in the absence of changes in vegetation composition, will not alter rates of litter decomposition in forests.     

Biodiversity correlates with regional patterns of forest litter pools

We compared litter pools of more than 1,000 forests differing in tree species diversity over a large scale in Catalonia (NE Spain). Monospecific forests always had smaller litter pools than mixed (from 2 to 5 tree species) forests. Whether there was a positive effect beyond two species mixtures depended on the species and functional identity of the dominant tree species. In sclerophyllous forests the positive effect of diversity was a step-function from one to more species. However, in conifers, litter pools increased constantly with tree diversity. The identity of the dominant tree species and functional type had also a significant effect on litter pools. For instance, forests dominated by sclerophyllous tree species had larger litter pools than forests dominated by deciduous and conifer tree species. When other forest structure parameters (i.e. tree basal area, wood production, successional stage, shrub cover and leaf area index) and environmental factors (i.e. mean annual temperature, mean annual precipitation, annual evapotranspiration and hillside position) where included in the analysis only leaf area index, basal area, wood production and mean temperature influenced litter pools positively. Our analysis emphasizes that at the regional scale, the litter compartment can be as influenced by biodiversity components as by other forest structure and climate components. In mixed forests, species and functional identity of the trees determine whether litter pools increase with tree diversity.     

Long-Term Effects of Frequent Low-Intensity Burning on the Abundance of Litter-Dwelling Invertebrates in Coastal Blackbutt Forests of Southeastern Australia

Low-intensity fire is extensively used in Australian dry eucalypt forests to reduce fuel levels. The long-term impact of this management practice on terrestrial invertebrates is, however, unknown and is of concern given their contribution to ecosystem function and forest biodiversity. This study found that areas subjected to frequent low-intensity fire had significantly lower numbers of spiders, ticks and mites, pseudoscorpions, woodlice, springtails, bugs, beetles, ants and insect larvae in the leaf litter compared with adjacent unburnt areas. Taxa numbers were between 41 and 82% lower and these reductions in abundance have led to an overall decline in taxon richness. This decrease was attributed to a reduction in the amount of litter and associated moisture levels, and a simplification of habitat structure. The extent of local and regional extinctions will depend upon the scale of this disturbance, with future studies investigating the impact on individual species within these communities. A comparison of two sampling techniques, pitfall-trapping and litter extraction, highlighted important considerations for spatial components of invertebrate sampling designs.     

青冈林土壤跳虫群落结构在落叶分解过程中的变化

1993年5月至1995年4月,用落叶代法研究青冈（Cyclobalanopsis glauca）落叶分解过程中跳虫的群落结构变化。用多样性指数、演替指数、相似系数分析跳虫在落叶分解过程中群落结构及其季节变化特点。青冈落叶分解经淋洗、养分固定 养分活化3个阶段,分解常数分别为k1=9.11,k2=2.57,k3=0.43（百分比／月）。跳中心在落叶分解过程中的集聚型分为3组：A组为落叶分解前期集聚的种类,B组为后期的种类,C组为中期或全过程的种类,分析讨论了落叶分解过程与跳虫功能群及群落结构变化的关系。     

Decomposition of woody branch litter on an altitudinal transect in the Himalaya

Decomposition of branch litter of four angiosperm and one conifer species was studied over a two-year period. Litter species and the corresponding forest type are: (i) Shorea robusta, sal forest at 329 m; (ii) Lyonia ovalifolia, mixed-pine broadleaf forest at 1 350 m; (iii) Pinus roxburghii, pine forest at 1 750 m; (iv) Quercus leucotrichophora, mixed oak-pine forest at 1 850 m; and (v) Quercus lanuginosa, mixed oak forest at 2 150 m. The weight loss ranged from 44–89%. Litter moisture and air temperature had significant positive effect on decomposition. The decomposition rate decreased with an increase in altitude and was inversely related with lignin content. Linear combinations of lignin content with rainfall and with temperature indicated significant interactive influence on decomposition.Authorities for plant names are given in Table 1.We gratefully acknowledge financial support from the Department of Science and Technology, Government of India.     

Parasites boost productivity: effects of mistletoe on litterfall dynamics in a temperate Australian forest

The importance of litter in regulating ecosystem processes has long been recognised, with a growing appreciation of the differential contribution of various functional plant groups. Despite the ubiquity of mistletoes in terrestrial ecosystems and their prominence in ecological studies, they are one group that have been overlooked in litter research. This study evaluated the litter contribution from a hemiparasitic mistletoe, Amyema miquelii (Lehm. ex Miq.) Tiegh., in an open eucalypt forest (Eucalyptus blakelyi, E. dwyeri and E. dealbata), at three scales; the forest stand, single trees and individual mistletoes. Litter from mistletoes significantly increased overall litterfall by up to 189%, the amount of mistletoe litter being proportional to the mistletoe biomass in the canopy. The high litter input was due to a much higher rate of mistletoe leaf turnover than that of host trees; the host litterfall and rate of leaf turnover was not significantly affected by mistletoe presence. The additional litter from mistletoes also affected the spatial and temporal distribution of litterfall due to the patchy distribution of mistletoes and their prolonged period of high litterfall. Associated with these changes in litterfall was an increase in ground litter mass and plant productivity, which reflects similar findings with root-parasitic plants. These findings represent novel mechanisms underlying the role of mistletoes as keystone resources and provide further evidence of the importance of parasites in affecting trophic dynamics.     

Litter decomposition rates in Canadian forests

The effect of litter quality and climate on the rate of decomposition of plant tissues was examined by the measurement of mass remaining after 3 years’ exposure of 11 litter types placed at 18 forest sites across Canada. Amongst sites, mass remaining was strongly related to mean annual temperature and precipitation and amongst litter types the ratio of Klason lignin to nitrogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean annual precipitation and Klason lignin:nitrogen ratio explained 73% of the variance in mass remaining for all sites and tissues. Using three doubled CO₂ GCM climate change scenarios for four Canadian regions, these relationships were used to predict increases in decomposition rate of 4–7% of contemporary rates (based on mass remaining after 3 years), because of increased temperature and precipitation. This increase may be partially offset by evidence that plants growing under elevated atmospheric CO₂ concentrations produce litter with high lignin:nitrogen ratios which slows the rate of decomposition, but this change will be small compared to the increased rate of decomposition derived from climatic changes.     

Litter quality, stream characteristics and litter diversity influence decomposition rates and macroinvertebrates

1. We examined the relative importance of litter quality and stream characteristics in determining decomposition rate and the macroinvertebrate assemblage living on autumn‐shed leaves. 2. We compared the decomposition rates of five native riparian tree species (Populus fremontii, Alnus oblongifolia, Platanus wrightii, Fraxinus velutina and Quercus gambelii) across three south‐western streams in the Verde River catchment (Arizona, U.S.A.). We also compared the decomposition of three‐ and five‐species mixtures to that of single species to test whether plant species diversity affects rate. 3. Decomposition rate was affected by both litter quality and stream. However, litter quality accounted for most of the variation in decomposition rates. The relative importance of litter quality decreased through time, explaining 97% of the variation in the first week but only 45% by week 8. We also found that leaf mixtures decomposed more quickly than expected, when all the species included were highly labile or when the stream environment led to relatively fast decomposition. 4. In contrast to decomposition rate, differences in the invertebrate assemblage were more pronounced across streams than across leaf litter species within a stream. We also found significant differences between the invertebrate assemblage colonising leaf mixtures compared with that colonising pure species litter, indicating non‐additive properties of litter diversity on stream invertebrates. 5. This study shows that leaf litter diversity has the capacity to affect in‐stream decomposition rates and stream invertebrates, but that these effects depend on both litter quality and stream characteristics.     

村落文化林与非文化林多尺度物种多样性加性分配

文化林是指村民按照文化传统、风俗习惯或宗教信仰自觉保护和管理的森林,具有一定社会文化功能。目前国内外对文化林物种多样性研究主要为定性描述,缺乏对文化林和非文化林生物多样性的定量比较及差异来源分析。利用物种多样性加性分配方法,将总的Gamma 多样性分成样格内的Alpha多样性以及样格间、样方间和林型间Beta多样性,对中国亚热带地区3个村落文化林的乔木层、灌木层、草本层和藤本层进行物种多样性的多尺度分析。调查发现:(1)文化林共有维管束植物296种,以苦槠,樟和米槠为优势种,非文化林共有维管束植物189种,以杉木、马尾松和毛竹为优势种。文化林乔木层和灌木层物种数显著高于非文化林,草本层和藤本层物种数差异不显著。(2)Beta多样性随尺度增大而增加,林型间Beta多样性最高,占区域总Gamma多样性的41.9%-62.8%,其次是样方间Beta多样性(18.6%-31.9%),对区域多样性贡献最小为样格内Alpha和样格间Beta多样性。(3)林型间的多样性对区域物种多样性的贡献中,文化林占主导作用,乔木层占54.4%-81.0%,灌木层占51.2%-60.2%,草本层占42.9%-64.1%,藤本层占49.9%-62.2%。(4) 物种累积-面积曲线表明,在各个尺度上,文化林物种多样性始终高于非文化林,从而在相同面积下保护了更多的物种。加性分配模型在多个空间尺度上阐明了Alpha和Beta多样性的变化,突出了文化林对区域物种多样性的贡献,对保护对象和保护范围的决策以及生物多样性的保护与恢复具有重要意义。     

福建建溪流域常绿阔叶防护林物种多样性特征研究

从生物多样性保护原则出发,物种多样性应是评价防护林综合效益的重要指标之一。本文采用Weibull分布模型分析建溪流域防护林乔木层、灌木层的种－多度关系,用多种公式计算防护林各层次的物种多样性并与我国暖温带落叶阔叶林的物种多样性相比较,得出以下结论：1)该流域防护林乔木层的种－多度关系符合Weibull分布模型,说明个体数量较多的乔木仅限于少数几种主要的树种,群落的均匀度相对较小;2)该流域防护林主要群落内乔木层、灌木层和草本层的丰富度、均匀度和总多样性指数都较我国暖温带落叶阔叶林相对应的指数高。     

More individuals but fewer species: testing the ‘more individuals hypothesis’ in a diverse tropical fauna

A positive relationship between species richness and productivity is often observed in nature, but the causes remain contentious. One mechanism, the ‘more individuals hypothesis’ (MIH), predicts richness increases monotonically with density, as a function of resource flux. To test the MIH, we manipulated resource abundance in a community of tropical rainforest litter ants and measured richness and density responses. A unimodal relationship between richness and density most closely fitted the control and disturbance (resource removal) treatments in contrast to expectations of the MIH. Resource addition resulted in a monotonic increase in richness relative to density, a shift from the pattern in the control. In the disturbance treatment, richness was greater than in the control, opposite to expectations of the MIH. While large-scale correlations between ant diversity and net primary productivity or temperature are reconcilable with the MIH, key elements of the hypothesis are not supported.     

木质藤本及其在热带森林中的生态学功能

木质藤本是热带森林的一个重要组分,直接或间接地影响着森林中树木的生长和更新,改变森林树木的种类组成,并且可以通过改变森林碳固定量等方式在生态系统水平上发挥作用。全球气候的变化,以及热带森林片断化程度的加剧,将很大程度上影响着木质藤本的多样性和丰富度,其特殊的生物学特性将在森林动态中发挥更加重要的作用。本文结合国内外目前木质藤本研究现状,概述了木质藤本的一般知识（包括木质藤本的定义和生物学特性等）,介绍了木质藤本全球分布格局、其多样性维持机理以及木质藤本在森林生态系统中的功能与作用,并就存在的一些问题以及需进一步开展的工作展开了讨论。     

不同生境中杉阔混交林物种多样性特征初步研究

根据生境因子应用主分量分析和动态聚类方法进行生境的划分,在此基础上分析不同生境中杉阔混交林群落数量特征。结果表明：不同生境中植物群落的主要优势种组成不一,其重要值也不同。不同生境中植物群落乔木层的物种数目、物种多样性、群落均匀度均有较大差异。海拔对不同生境中植物群落乔木层的物种数目、物种多样性和群落均匀度有很大影响,坡向则对个体总数和种类的影响较大。海拔和坡向对不同生境中植物群落乔木层生态优势度则无明显影响,应该重视不同生境中杉阔混交林多样性的保护。     

Isopod effects on decomposition of litter produced under elevated CO2, N deposition and different soil types

The performance of Oniscus asellus (Isopoda) and its influence on litter mass loss and mineralization was assessed in a microcosm experiment, using beech (Fagus sylvatica) leaf litter that was produced on different soil types, contrasting atmospheric CO₂ concentrations, and different nitrogen deposition rates. Litter quality was significantly altered by these treatments, and many of the CO₂ and N effects differed between soil types. Litter quality affected subsequent litter mass loss rates, microbial respiration, and leaching of dissolved organic carbon (DOC) and nitrate. These effects were largely independent of the presence of isopods, even though isopods highly accelerated litter mass loss, stimulated microbial respiration by 37%, and increased nitrate leaching by 50%. Isopods did not change their relative rates of litter consumption and growth in response to litter quality. Isopod mortality, however, increased with increasing litter lignin/N ratios, and was significantly different between soil types, which may indicate long‐term effects on litter decomposition through altered isopod densities. Having the choice among the litter of three different species [maple (Acer pseudoplatanus), beech (Fagus sylvatica) and oak (Quercus robur)] grown at either ambient or elevated CO₂, isopods preferred maple to beech when all the litter was produced under elevated CO₂. This suggests that beyond changes in consumption, an altered food selection by isopods in a CO₂‐enriched atmosphere may affect the temporal and spatial composition of the litter layer in temperate forests. In contrast to previous findings, we conclude that isopods do not always increase their consumption rates, and hence do not differentially affect microbial decomposition in litter of poorer quality. Nevertheless changes in animal densities and/or shifts in their food preferences, could result in altered decomposition and carbon and nutrient turnover rates.