黏菌物种多样性及其与影响因子关系的研究进展

黏菌是一类具有独特特征且广泛分布在陆地生态系统中的菌物,具有调节微生境微生物群落、影响营养和生物量分配等作用。黏菌的物种多样性及影响因素一直是黏菌生态学的研究热点。本文综述了不同微生境中黏菌的发生情况以及影响黏菌物种多样性的非生物因子和生物因子3个方面的研究进展,进一步揭示黏菌在生态系统中的生态功能。     

水电开发对河岸植被影响研究进展

河岸植被是河流生态系统的重要组成部分, 在维持河流生态系统完整性和河岸生物多样性保护方面具有重要作用。目前, 水电开发影响下河岸植被的物种组成、多样性、种间关联等几方面日益受到关注, 是河流生态学研究中的重要热点。文章阐述了水电开发后河流水文、河岸生境、繁殖体扩散、外来物种入侵等影响下河岸植被的响应机制。探讨了河岸植被与生态环境的相关性, 提出了今后河岸植被与水电开发相互作用机制, 及水电开发的正负生态效应综合影响研究。     

固氮类植物在陆地生态系统中的作用研究进展

固氮类植物是陆地生态系统中的一个重要功能群,它们广泛存在于陆地生态系统中,是陆地生态系统最重要的氮源,大量研究表明,固氮类植物在陆地生态系统中的生态功能表现出明显的复杂性和多样性,对于生态过程有很强的主导性和控制性.通过与固氮微生物形成不同的共生固氮类型,它们可以改善土壤结构和营养组成以及地表微生境,直接影响碳氮磷循环、种子萌发和植株生长、植被演替、凋落物构成及其分解4个关键生态过程,进而提高群落结构复杂性、生物多样性和初级生产力,促进植被恢复和减少水土流失.未来研究中,应该加强对陆地生态系统固氮过程的定量化分析,确定影响共生固氮的主导因子和生态机制从而为陆地系统的生态恢复提供依据.     

东苕溪中下游河岸类型对鱼类多样性的影响

河流修复工程被美国《科学》杂志列入2000年最具发展潜力的六大领域之一,河流修复工程对水生生态系统的影响也成为各国科学家的研究热点。本文以东苕溪中下游河段为对象,研究4种不同河岸类型（自然河岸 水生植物（A）、自然河岸 无水生植物（B）、人工河岸 水生植物（C）、人工河岸 无水生植物（D））对鱼类生物多样性的影响。本次调查共采集鱼类标本499尾,经鉴定为32种,隶属于7目10科24属。鱼类生物多样性结果显示A、B的物种丰度和Shannon-Wiener指数与D存在显著差异（P<0.05）; A的优势度指数与D存在显著性差异（P<0.05）; A、C的均匀度与D存在显著性差异。鱼类群落NMDS排序与相似性分析（ANOSIM）显示D与A、B、C能完全分开,且D与A、C存在显著性差异（P<0.05）,其中A与C存在显著性差异。因此,河流修复工程中水生植被的恢复对于水生生物多样性的维持至关重要,且恢复水生植被的河流修复工程会减少该工程对鱼类群落结构和生物多样的负面影响。     

以枯叶蛱蝶属为例揭示山地生物多样性演化和遗传机制

<正>生物多样性的成因是生物学中的核心问题之一。陆地环境中,山区生态系统蕴藏着丰富的陆地生物多样性。山地环境中巨大的海拔梯度变化形成了多样的微环境,为种群的分化提供了条件[1]。因此,山地生物区系及其与低地生物多样性热点的关系为人们理解多样性的形成原因提供了重要的切入点。枯叶蛱蝶属(Kallima)蝴蝶物种丰富,在山地和低海拔的生物热点地区均有分布,是研究山地物种多样性产生机制的理想系统。     

冰川及雪线后退对河流水生生物影响的研究进展

冰川影响下的河流形成了独特的冷水生态系统, 为水生生物提供了多样的栖息地。然而在全球气候变暖的背景下, 冰川和积雪不断退缩、甚至加速消融, 破坏了原有的水生生态系统。文章综述了国内外有关冰川积雪融水对河流水生生物及环境因子影响的研究现状, 探讨了冰川流域水生生物研究存在的问题及未来相关的方向。冰川积雪融水对河流水生生物的群落结构及遗传多样性产生了不同程度的影响。同时某些水生生物在形态、生活史和行为适应能力等方面也产生了抵抗极端环境的进化。笔者提出应重点关注水生生物对冰川和积雪退化的响应机制与变化趋势, 以期为冰川流域水生生物多样性及保护提供一定依据。     

内蒙古草原凋落物分解对生物多样性变化的响应

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。     

滨岸带对河流生态系统的影响机制研究进展

从水文调节、水质改善、物质输入调控、生物多样性维持等方面梳理了滨岸带对河流生态系统的影响机制。滨岸带具有良好的水文调节效应, 这种调节效应主要通过滨岸带植被根系对土壤水分持留, 植物残体对径流路径的影响, 以及挺水和沉水植物对水流的物理作用等途径实现。滨岸带显著影响水质过程, 对于面源污染径流具有较好的净化效果。滨岸带能够经历周期性的干湿交替, 同时具有发达的植被系统和丰富的土壤微生物类型, 独特的水文和地球化学条件使滨岸带成为氮磷迁移转化的热区。滨岸带对水生态系统的物质输入起到重要的调控作用, 既能够为水体生态系统提供丰富的物质来源, 又能够避免过量的营养物质输入。这种调控作用对于水生态系统群落结构的维持和生态系统功能的发挥具有重要意义。滨岸带水生和湿生植被的生长使水体生态系统食物链不断完善, 大型无脊椎生物和鱼类种群数量得以增加, 对水体生物多样性的提升具有明显的贡献。自然的洪水扰动可能是滨岸带生物多样性的维持机制, 而水媒传播过程则可能是滨岸带影响河流生物多样性的重要机制。当前对于滨岸带生态机制过程的认识尚不够深入, 今后滨岸带研究要加强物质过程和生态学过程的探讨, 尤其是水文、水质、生物群落等要素的耦合机制, 滨岸带水环境效应的模拟预测, 以及滨岸带对河流生物多样性的影响机制研究等。     

河岸植被缓冲带主要生态服务功能研究的现状与展望

河岸植被缓冲带是河流生态系统和陆地生态系统之间的生态交错带,具有独特的生态系统结构和服务功能,也是近年来生态学和环境科学研究的热点之一.本文对河岸带的生态系统结构及其在生物多样性维持、非点源氮素污染防治等主要生态服务功能方面的研究进行了系统总结和分析.由于岸边缓冲带具有结构复杂、系统内外干扰因子多、时空异质性强等特征,要实现对河岸带生态系统的科学有效管理,还需要进行大量的理论和案例研究.从系统生态学和景观生态学的角度,展望了该领域的研究前景:(1)加强人类活动干扰如土地利用的时空变化对河岸区域生物多样性分布特征和生态环境效应的影响研究;(2)加强不同河岸植被缓冲带结构和区域环境特征对非点源氮素污染净化机理和控制过程的研究;(3)在小尺度长期定位观测和机理研究的基础上,综合运用数学方法、遥感(RS)和地理信息系统(GIS)等工具,开发适合我国地域特点和环境特征的生态系统管理模型,定量研究河岸带生态系统结构、过程与功能动态变化及其与人类活动干扰之间的相互关系和影响机制,为区域社会经济的可持续发展提供科学依据和管理对策.     

湿地生物地球化学过程研究进展

1　湿地生物地球化学过程的概念及内涵营养物质在生态系统之间的输入和输出以及在生物各圈层之间进行的物质和能量交换称为生物地球化学循环 (ｂｉｏｇｅｏｃｈｅｍｉｃａｌｃｉｒｃｕｌａｔｉｏｎ) [4 ] ,它实质上是指生物有机体及其产物与无机环境之间进行的物质交换和能量转换过程。湿地是介于陆地生态系统和水生生态系统之间的过渡地带[3 ] ,它是一种特殊的生态系统 ,其独特多样的生物条件显著影响着生物地球化学过程。这些过程不仅改变了物质的化学组成 ,而且使它们在湿地内发生空间位移以及生物地球化学转化。湿地生物地球化学过程是…     

Butterflies as an indicator group of riparian ecosystem assessment

Riparian ecosystems play an important role in modulating a range of ecosystem processes that affect aquatic and terrestrial organisms. Butterflies are a major herbivore in terrestrial ecosystems and are also common in riparian ecosystems. Since butterflies use plants for larval food and adult nectar sources in riparian ecosystems, butterfly diversity can be utilized to evaluate riparian ecosystems. We compiled butterfly data from 33 sites in three riparian ecosystem types across the country and compared butterfly diversity in terms of number of species and quality index in relation to riparian environmental variables. Number of butterfly and plant species was not different among three riparian habitat types. Additionally, there was no significant ecological variable to distinguish the butterfly communities on three riparian habitats. Non-metric multi-dimensional scaling ordination showed that butterfly communities in three riparian ecosystem types differed from each other, and butterfly riparian quality index was the main variable for butterfly assemblages. Five indicator species for moor and another five species for riverine riparian ecosystems were identified. Three and one indicator species for moor and riparian ecosystems, respectively, were plant specialists, while 44 butterflies were general feeders, feeding on a wide range of hostplants in several habitats. These results suggest that butterfly species use actively riparian habitats for nectar and larval food, and the butterfly riparian quality index can be employed to track faunal change in riparian habitats, which are frequently threatened by disturbances such as water level and climate changes, and invasive species.     

Complex hydromorphology of meanders can support benthic invertebrate diversity in rivers

In freshwater environments, high biodiversity is commonly associated with habitat heterogeneity. River bends and meanders are particularly complex morphodynamic elements of watercourses. However, the specific spatio-temporal interactions between hydromorphology and the resident biota have scarcely been studied. This article reviews the relationships between hydraulic processes, and morphological units that are typical for meanders, and analyzes the concomitant spatial and temporal dynamics of habitats suitable for aquatic invertebrates. Flow in river bends is characterized by significant cross-stream velocities, which modify primary flow patterns, and create helical flow trajectories. Consequently, boundary shear stresses at the river-bed are altered, so that complex erosion, transport, and accumulation processes characteristically shape bed and bank morphology. The diversity of substrate types and complex bathymetry in meanders provide a large variety of habitat conditions for benthic invertebrates within a relatively small spatial domain, which are connected via hydraulic pathways. Periodic reversal of hydro-morphological processes between low and high flow, and seasonal growth of aquatic macrophytes creates spatio-temporal dynamics at the meso- and microhabitat scales. Such habitat dynamics increases benthic invertebrate diversity to the extent it is consistent with spatio-temporal scales of invertebrate mobility and life cycle. Furthermore, the presence of flow refugia, and hydraulic dead zones in meanders is essential to sustain species richness. This study concludes that meanders are highly complex morphodynamic elements that exhibit several self-regulating principles supporting invertebrate diversity and resilience in fluvial ecosystems.     

Spatial and temporal aquatic–terrestrial transitions in the temporary Albarine River,France: responses of invertebrates to experimental rewetting

1. In temporary rivers, viewed as coupled terrestrial–aquatic ecosystems, spatial and temporal transition zones between aquatic and terrestrial conditions are common and occur simultaneously. 2. The effects of artificial rewetting on terrestrial and aquatic invertebrate assemblages were examined in dry sediments collected from the Albarine River, France. Rewetted sediments had previously been dry for between 0.1 and 142 days. Dry sediments were collected directly from the streambed (DS) and from riparian gravel bars (RGB). 3. We first predicted that invertebrate responses to rewetting would vary with the duration of the preceding dry period. Second, we predicted convergence of the invertebrate assemblages in DS and RGB sediments with increasing duration of the dry period. Third, we predicted that an aquatic ‘invertebrate seedbank’ (aquatic life stages that persist within streambed sediments during dry periods) would contribute substantially to the resilience of benthic assemblages. 4. Results indicated that the duration of the dry period was the primary driver of aquatic and terrestrial responses to artificial rewetting. The density and richness of aquatic taxa decreased with the duration of the dry period in both DS and RGB sediments, whereas the density of terrestrial invertebrates increased in DS sediments. 5. No convergence between DS and RGB assemblage composition was observed with an increasing dry period. Although there were more aquatic organisms in DS sediments than in RGB sediments, there was no difference in taxonomic richness between sediment types. Even after prolonged dry periods (142 days), there was typically a lower density and taxonomic richness of terrestrial invertebrates in DS sediments than in adjacent RGB sediments. 6. The results suggest that the aquatic invertebrate seedbank could contribute substantially to the resilience of benthic assemblages in the Albarine River, in addition to other mechanisms such as drift and oviposition. Of the taxa in the benthos before and after the summer dry period, 65% were also recovered from artificially rewetted DS sediments. The simultaneous presence of temporal and spatial terrestrial–aquatic transition zones in temporary rivers increases successional diversity (i.e. mosaics of dry and saturated streambed patches at various stages of terrestrial and aquatic succession). This contribution to biodiversity emphasises the need to protect dry reaches of temporary rivers.     

More than a barrier: The complex effects of ecotone vegetation type on terrestrial consumer consumption of an aquatic prey resource

Community structure and dynamics can be influenced by resource transfers between ecosystems, yet little is known about how boundary structure determines both the magnitude of exchanges and their effects on recipient and donor communities. Aquatic and terrestrial ecosystems are often linked by resource fluxes and riparian vegetation is commonly affected by anthropogenic alterations to land use or river hydrological regime. I investigated whether shrubs at the freshwater–terrestrial interface alter the supply, distribution and importance of aquatic prey resources to terrestrial consumers. Shrubs were predicted to alter the larval community composition of aquatic insects and the emergence of winged adults, thus affecting aquatic prey subsidies to terrestrial consumers. In addition, shrubs were hypothesized to alter the microclimatic suitability of the riparian zone for adult aquatic insects, act as a physical barrier to their dispersal and affect terrestrial community composition, particularly the abundance and type of predators that could benefit from the aquatic prey resource. Stable isotope dietary analyses and a survey of shrub‐dominated and open grassland riparian habitats revealed that larval densities of aquatic insects (EPTM: Ephemeroptera, Plecoptera, Trichoptera and Megaloptera) were higher in shrub than grassland habitats; however, reduced emergence and lateral dispersal in shrub areas led to lower densities of adults. The temperature and relative humidity of the riparian zone did not differ between the habitats. Ground‐active terrestrial invertebrate communities had a higher proportion of cursorial spiders in grassland, coinciding with greater abundances of aquatic prey. Aquatic prey contribution to cursorial spider diet matched adult aquatic insect abundances. Overall, riparian shrubs reduced the magnitude, or at least altered the timing, of cross‐ecosystem subsidy supply, distribution and use by consumers through mechanisms operating in both the aquatic and terrestrial ecosystems. Thus, the structure of ecosystem boundaries has complex effects on the strength of biological interactions between adjacent systems.     

The boundaries of river systems: the metazoan perspective

1. This overview of metazoans associated with the riparian/groundwater interface focuses on the fauna inhabiting substratum interstices within the stream bed and in alluvial aquifers beneath the floodplain. The objective is to integrate knowledge of habitat conditions and ecology of the interstitial fauna into a broad spatiotemporal perspective of lotic ecosystems. 2. Most aquatic metazoans of terrestrial ancestry, secondarily aquatic forms including insects and water mites (Hydracarina), are largely confined to surface waters (epigean), most of the time penetrating only the superficial interstices of the stream bed. 3. Primary aquatic metazoans include crustaceans and other groups whose entire evolutionary histories took place in water. Some species are epigean, whereas other members of the primary aquatic fauna are true subterranean forms (hypogean ) , residing deep within the stream bed and in alluvial aquifers some distance laterally from the channel. 4. The hypogean/epigean affinities of interstitial animals are reflected in repetitive gradients of species distribution patterns along vertical (depth within the stream bed), longitudinal (riffle/pool), and lateral (across the floodplain) spatial dimensions, as well as along recovery trajectories following floods (temporal dimension). 5. Fluvial dynamics and sediment characteristics interact to determine hydraulic conductivity, oxygen levels, pore space, particle size heterogeneity, organic content and other habitat conditions within the interstitial milieu. 6. Multidimensional environmental gradients occur at various scales across riparian/groundwater boundary zones. The spatiotemporal variability of hydrogeomorphological processes plays an important role in determining habitat heterogeneity, habitat stability, and connectivity between habitat patches, thereby structuring biodiversity patterns across the riverine landscape. 7. The erosive action of flooding maintains a diversity of hydrarch and riparian successional stages in alluvial floodplains. The patchy distribution patterns of interstitial communities at the floodplain scale reflect, in part, the spatial heterogeneity engendered by successional processes. 8. Interstitial metazoans engage in passive and active movements between surface waters and ground waters, between aquatic and riparian habitats, and between different habitat types within the lotic system. Some of these are extensive migrations that involve significant exchange of organic matter and energy between ecosystem compartments. 9. The generally high resilience of lotic ecosystems to disturbance is attributable, in part, to high spatiotemporal heterogeneity. Habitat patches less affected by a particular perturbation may serve as ’refugia ‘; from which survivors recolonize more severely affected areas. Mechanisms of refugium use may also occur within habitats, as, for example, through ontogenetic shifts in microhabitat use. Rigorous investigations of interstitial habitats as refugia should lead to a clearer understanding of the roles of disturbance and stochasticity in lotic ecosystems. 10. Development of realistic ’whole river ‘; food webs have been constrained by the exclusion of interstitial metazoans, which may in fact contribute the majority of energy flow in lotic ecosystems. A related problem is failure to include groundwater/riparian habitats as integral components of alluvial rivers. A conceptual model is presented that integrates groundwater and riparian systems into riverine food webs and that reflects the spatiotemporal complexity of the physical system and connectivity between different components. 11. Interstitial metazoans also serve as ’ecosystem engineers, ‘; by influencing the availability of resouces to other species and by modifying habitat conditions within the sediment. For example, by grazing on biofilm, interstitial animals may markedly stimulate bacterial growth rates and nutrient dynamics. 12. Although there has been a recent surge of interest in the role of interstitial animals in running waters, the knowledge gaps are vast. For example, basic environmental requirements of the majority of groundwater metazoans remain uninvestigated. Virtually nothing is known regarding the role of biotic interactions in structuring faunal distribution patterns across groundwater/riparian boundary zones. Interstitial metazoans may contribute significantly to the total productivity and energy flow of the biosphere, but such data are not available. Nor are sufficient data available to determine the contribution of groundwater animals to estimates of global biodiversity. 13. Effective ecosystem management must include groundwater/riparian ecotones and interstitial metazoans in monitoring and restoration efforts. Evidence suggests that a ’connected ‘; groundwater/riparian system provides natural pollution control, prevents clogging of sediment interstices and maintains high levels of habitat heterogeneity and successional stage diversity. River protection and restoration should maintain or re-establish at least a portion of the natural fluvial dynamics that sustains the ecological integrity of the entire riverine–floodplain–aquifer ecosystem. Keywords: groundwater/riparian ecotones, hyporheic habitat, epigean, hypogean, interstitial fauna, biodiversity, food webs     

Woody debris and terrestrial invertebrates – effects on prey resources for brown trout (Salmo trutta) in a boreal stream

Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factors affected potential food resources for drift-feeding brown trout (Salmo trutta ) in a boreal Swedish forest stream. Specifically, we followed the effects on the abundance of aquatic and terrestrial invertebrate fauna from June to August 2007. The treatments were 1) addition of wood, unmanipulated terrestrial invertebrate inputs, 2) reduction of terrestrial invertebrate inputs (using canopy covers), no addition of wood, 3) unmanipulated ambient conditions, 4) simultaneous addition of wood and reduction of terrestrial invertebrate inputs. Added wood resulted in greater biomass of aquatic invertebrate biomass, and both input and drift of terrestrial invertebrates were reduced by canopy covers. In terms of total potential prey biomass, the addition of wood with ambient levels of terrestrial invertebrate inputs had the highest standing crop of benthic, wood-living and terrestrial invertebrates combined, whereas the treatment with reduced terrestrial input and no wood added had the lowest standing crop. Our study indicates that forest practices that both reduce the recruitment of wood and the input of terrestrial invertebrates to small streams have negative effects on prey availability for drift-feeding brown trout. The positive effects of wood addition on biomass of aquatic macroinvertebrates may partly compensate for the negative effects of reduced terrestrial invertebrate subsidies.     

Responses to River Inundation Pressures Control Prey Selection of Riparian Beetles

Background

Riparian habitats are subjected to frequent inundation (flooding) and are characterised by food webs that exhibit variability in aquatic/terrestrial subsidies across the ecotone. The strength of this subsidy in active riparian floodplains is thought to underpin local biodiversity. Terrestrial invertebrates dominate the fauna, exhibiting traits that allow exploitation of variable aquatic subsidies while reducing inundation pressures, leading to inter-species micro-spatial positioning. The effect these strategies have on prey selection is not known. This study hypothesised that plasticity in prey choice from either aquatic or terrestrial sources is an important trait linked to inundation tolerance and avoidance.

Method/Principal Findings

We used hydrological, isotopic and habitat analyses to investigate the diet of riparian Coleoptera in relation to inundation risk and relative spatial positioning in the floodplain. The study examined patch scale and longitudinal changes in utilisation of the aquatic subsidy according to species traits. Prey sourced from terrestrial or emerging/stranded aquatic invertebrates varied in relation to traits for inundation avoidance or tolerance strategies. Traits that favoured rapid dispersal corresponded with highest proportions of aquatic prey, with behavioural traits further predicting uptake. Less able dispersers showed minimal use of aquatic subsidy and switched to a terrestrial diet under moderate inundation pressures. All trait groups showed a seasonal shift in diet towards terrestrial prey in the early spring. Prey selection became exaggerated towards aquatic prey in downstream samples.

Conclusions/Significance

Our results suggest that partitioning of resources and habitat creates overlapping niches that increase the processing of external subsidies in riparian habitats. By demonstrating functional complexity, this work advances understanding of floodplain ecosystem processes and highlights the importance of hydrological variability. With an increasing interest in reconnecting rivers to their floodplains, these invertebrates represent a key functional element in ensuring that such reconnections have demonstrable ecological value.     

Stream salinization is associated with reduced taxonomic,but not functional diversity in a riparian plant community

Abstract Dryland salinity presents an overwhelming threat to terrestrial and aquatic habitats in Australia, and yet there remains very little empirical evidence of the impacts of secondary salinization on the biodiversity of riparian communities. Here we describe the response of a riparian plant community to stream and soil salinization, 25 years after the experimental clearing of a catchment in south‐western Australia. Riparian plant species diversity was inversely related to soil salinity, and plant species composition was significantly altered by increased soil salinity. Despite the evidence for an impact of salinization on the taxonomic diversity and composition of the riparian plant community, there was little evidence for any effect of salinization on functional group diversity, or on ecological functioning, as measured by the percentage of above‐ground plant cover.     

Ecosystem Linkages between Southern Appalachian Headwater Streams and Their Banks: Leaf Litter Breakdown and Invertebrate Assemblages

We examined red maple (Acer rubrum L.) leaf litter breakdown in streams and riparian zones at two sites in the southern Appalachian Mountains to understand how differences in abiotic and biotic factors influence leaf breakdown rates. Litterbags were placed in three riparian habitats differing in litter layer moisture: stream > bank > upland. Invertebrates colonizing litterbags at one site were also examined to determine how variations in community and functional structure affect breakdown rates. Leaves broke down fastest in streams and slowest in upland habitats, whereas bank habitats were intermediate and characterized by high variability. Faster leaf breakdown rates in streams appeared to be a function of greater moisture availability, a more stable thermal regime, and a higher biomass of leaf-shredding invertebrates, especially the stonefly Tallaperla. In addition, patterns of leaf breakdown and invertebrate community structure provided evidence for a stronger than expected ecological connection between the stream and the bank. Overall, detritus processing within this narrow riparian ecosystem varied considerably depending on the availability of moisture. Results from this study show that stream channel–floodplain interactions in riparian ecosystems of steep forested mountains are analogous to ones in larger downstream or low-gradient systems. Riparian zones throughout a river network display a remarkable heterogeneity in their ability to process organic matter, which is ultimately driven by changes in hydrological conditions. Received 6 March 2001; accepted 3 July 2001.