Spatial heterogeneity in water velocity drives leaf litter dynamics in streams

1. Stream hydro-morphology refers to the heterogeneous distribution of hydrologic conditions that occur above a complex benthic surface such as a streambed.
2. We hypothesised that hydro-morphological conditions will influence the retention, re-distribution, and microbial-driven decomposition of leaf litter inputs in stream ecosystems because each process varies with overlying water velocity.
3. We tested this hypothesis using: (1) the spatial distribution of water velocity within a stream reach as a surrogate of stream hydro-morphology; (2) leaf tracer (i.e. Ginkgo biloba L.) additions with serial recovery to examine the relationship between benthic retention and overlying velocity; and (3) measurements of leaf litter decomposition (i.e. Alnus glutinosa [L.] Gaertn.) under different water velocity conditions.
4. Results demonstrate that water velocity exerts a significant influence on the retention and re-distribution of leaf litter inputs within the reach. The observed range of water velocity (from c. 0 to 0.92 cm/s) also strongly influences the range of leaf litter decomposition rates (0.0076–0.0222/day).
5. Our findings illustrate that water velocity influences leaf litter dynamics in streams by controlling leaf litter transport, retention and re-distribution as well as how leaves decompose within recipient stream reaches. Ultimately, the results show that the efficiency of leaf litter inputs in supporting stream ecosystem function is dependent on the hydro-morphological characteristics of the receiving stream ecosystems.

     

Leaf litter transport and retention in a tropical Rift Valley stream: an experimental approach

The impact of a drought on freshwater snail and trematode communities was investigated in a lake. Before the drought, 15 gastropod species (Valvatidae, Planorbidae, Lymnaeidae, Ancylidae, Physidae) and 10 trematode species (cercariaeum, xiphidiocercariae, echinostome, furcocercariae, notocotyle, lophocercous) were recorded. The rate of parasitism was 5.13% and there were 11 host species. The 2 major consequences of desiccation were the disappearance of snails, except Valvata piscinalis and Lymnaea peregra, and the absence of trematodes infecting the surviving snails. As soon as favourable conditions were restored, the littoral area was recolonized, first by hygrophilic and amphibious species, second by aquatic species. Nine months after the drought, the gastropod community was restored. Recolonization by the trematodes was delayed compared with that of gastropods. During the study, the overall prevalence was equal to 0.36% and only 4 trematode species and 5 host species were recorded. Because of the great variability of freshwater ecosystems, long-term studies are necessary to understand the dynamics of snail and trematode populations and determine the regulatory effect of parasitism in the field.     

Effects of organic matter and season on leaf litter colonisation and breakdown in cave streams

1. Low organic matter availability is thought to be a primary factor influencing evolutionary and ecological processes in cave ecosystems. We examined links among organic matter abundance, macroinvertebrate community structure and breakdown rates of red maple (Acer rubrum) and corn litter (Zea mays) in coarse‐ (10 × 8 mm) and fine‐mesh (500‐μm) litter bags over two seasonal periods in four cave streams in the south‐eastern U.S.A. 2. Organic matter abundance differed among cave streams, averaging from near zero to 850 g ash‐free dry mass m^?2. Each cave system harboured a different macroinvertebrate community. However, trophic structure was similar among caves, with low shredder biomass (2–17% of total biomass). 3. Corn litter breakdown rates (mean k = 0.005 day^?1) were faster than red maple (mean k = 0.003 day^?1). Breakdown rates in coarse‐mesh bags (k = 0.001–0.012 day^?1) were up to three times faster than in fine‐mesh bags (k = 0.001–0.004 day^?1). Neither invertebrate biomass in litter bags nor breakdown rates were correlated with the ambient abundance of organic matter. Litter breakdown rates showed no significant temporal variation. Epigean (surface‐adapted) invertebrates dominated biomass in litter bags, suggesting that their effects on cave ecosystem processes may be greater than hypogean (cave‐adapted) taxa, the traditional focus of cave studies. 4. The functional diversity of our cave communities and litter breakdown rates are comparable to those found in previous litter breakdown studies in cave streams, suggesting that the factors that control organic matter processing (e.g. trophic structure of communities) may be broadly similar across geographically diverse areas.     

Similar breakdown rates and benthic macroinvertebrate assemblages on native and Eucalyptus globulus leaf litter in Californian streams

1. Eucalyptus globulus, a tree species planted worldwide in many riparian zones, has been reported to affect benthic macroinvertebrates negatively. Although there is no consensus about the effects of Eucalyptus on aquatic macrobenthos, its removal is sometimes proposed as a means of ecological restoration. 2. We combined the sampling of macroinvertebrates with measurement of the colonisation of leaf packs in mesh bags, to examine the effects of riparian Eucalyptus and its litter on benthic macroinvertebrates in three small streams in California, U.S.A. Each stream included one reach bordered by Eucalyptus (E‐site) and a second bordered by native vegetation (N‐site). 3. The macrobenthos was sampled and two sets of litter bags were deployed at each site: one set with Eucalyptus litter (Euc‐bags) and one with mixed native tree litter (Nat‐bags) containing Quercus, Umbellularia, Acer and Alnus. Bags were exposed for 28, 56 and 90 days and this experiment was repeated in the autumn, winter and spring to account for effects of changing stream flow and insect phenology. 4. Litter input (average dry mass: 950 g m^?2 year^?1 in E‐sites versus 669 g m^?2 year^?1 in N‐sites) was similar, although in‐stream litter composition differed between E‐ and N‐sites. Litter broke down at similar rates in Euc‐bags and Nat‐bags (0.0193 day^?1 versus 0.0134 day^?1), perhaps reflecting the refractory nature of some of the leaves of the native trees (Quercus agrifolia). 5. Summary metrics for macroinvertebrates (taxon richness, Shannon diversity, pollution tolerance index) did not differ significantly between the E and N sites, or between Euc‐bags and Nat‐bags. No effect of exposure time or site was detected by ordination of the taxa sampled. However, distinct seasonal ordination clusters were observed in winter, spring and autumn, and one of the three streams formed a separate cluster. 6. The presence of Eucalyptus was less important in explaining the taxonomic composition of the macrobenthos than either ‘season’ or ‘stream’. Similarly, these same two factors (but not litter species) also helped explain the variation in leaf breakdown. We conclude that patches of riparian Eucalyptus and its litter have little effect on stream macrobenthos in this region.     

雪被斑块对高山森林两种灌木凋落叶质量损失的影响

高山/亚高山森林灌木层植物凋落物的分解对于系统物质循环等过程具有重要意义, 并可能受到冬季不同厚度雪被斑块下冻融格局的影响。该文采用凋落物分解袋法, 研究了高山森林典型灌层植物华西箭竹(Fargesia nitida)和康定柳(Salix paraplesia)凋落物在沿林窗-林下形成的冬季雪被厚度梯度(厚型雪被斑块、较厚型雪被斑块、中型雪被斑块、薄型雪被斑块、无雪被斑块)上在第一年不同关键时期(冻结初期、冻结期、融化期、生长季节初期和生长季节后期)的质量损失特征。在整个冻融季节, 华西箭竹和康定柳凋落叶的平均质量损失分别占全年的(48.78 ± 2.35)%和(46.60 ± 5.02)%。冻融季节雪被覆盖斑块下凋落叶的失重率表现出厚型雪被斑块大于薄型雪被斑块的趋势,而生长季节无雪被斑块的失重率明显较高。尽管如此, 华西箭竹凋落物第一年分解表现出随冬季雪被厚度增加而增加的趋势, 但康定柳凋落物第一年失重率以薄型雪被斑块最高, 而无雪被斑块最低。同时, 相关分析表明冻融季节凋落叶的失重率与平均温度和负积温呈极显著正相关, 生长季节凋落叶的失重率与所调查的温度因子并无显著相关关系, 但全年凋落物失重率与平均温度和正/负积温均显著相关。这些结果清晰地表明, 未来冬季变暖情境下高山森林冬季雪被格局的改变将显著影响灌层植物凋落物分解, 影响趋势随着物种的差异具有明显差异。     

Drivers of litter mass loss and faunal composition of detritus patches change over time

Decomposition of vegetal detritus is one of the most fundamental ecosystem processes. In complex landscapes, the fate of litter of terrestrial plants may depend on whether it ends up decomposing in terrestrial or aquatic conditions. However, (1) to what extent decomposition rates are controlled by environmental conditions or by detritus type, and (2) how important the composition of the detritivorous fauna is in mediating decomposition in different habitats, remain as unanswered questions. We incubated two contrasting detritus types in three distinct habitat types in Coastal Georgia, USA, to test the hypotheses that (1) the litter fauna composition depends on the habitat and the litter type available, and (2) litter mass loss (as a proxy for decomposition) depends on environmental conditions (habitat) and the litter type. We found that the abundance of most taxa of the litter fauna depends primarily on habitat. Litter type became a stronger driver for some taxa over time, but the overall faunal composition was only weakly affected by litter type. Decomposition also depends strongly on habitat, with up to ca. 80% of the initial detrital mass lost over 25 months in the marsh and forest habitats, but less than 50% lost in the creek bank habitat. Mass loss rates of oak versus pine litter differed initially but converged within habitat types within 12 months. We conclude that, although the habitat type is the principle driver of the community composition of the litter fauna, litter type is a significant driver of litter mass loss in the early stages of the decomposition process. With time, however, litter types become more and more similar, and habitat becomes the dominating factor in determining decomposition of older litter. Thus, the major driver of litter mass loss changes over time from being the litter type in the early stages to the habitat (environmental conditions) in later stages.     

Riparian leaf litter decomposition on pond bottom after a retention on floating vegetation

Allochthonous (e.g., riparian) plant litter is among the organic matter resources that are important for wetland ecosystems. A compact canopy of free‐floating vegetation on the water surface may allow for riparian litter to remain on it for a period of time before sinking to the bottom. Thus, we hypothesized that canopy of free‐floating vegetation may slow decomposition processes in wetlands. To test the hypothesis that the retention of riparian leaf litter on the free‐floating vegetation in wetlands affects their subsequent decomposition on the bottom of wetlands, a 50‐day in situ decomposition experiment was performed in a wetland pond in subtropical China, in which litter bags of single species with fine (0.5 mm) or coarse (2.0 mm) mesh sizes were placed on free‐floating vegetation (dominated by Eichhornia crassipes, Lemna minor, and Salvinia molesta) for 25 days and then moved to the pond bottom for another 25 days or remained on the pond bottom for 50 days. The leaf litter was collected from three riparian species, that is, Cinnamomum camphora, Diospyros kaki, and Phyllostachys propinqua. The retention of riparian leaf litter on free‐floating vegetation had significant negative effect on the carbon loss, marginal negative effects on the mass loss, and no effect on the nitrogen loss from leaf litter, partially supporting the hypothesis. Similarly, the mass and carbon losses from leaf litter decomposing on the pond bottom for the first 25 days of the experiment were greater than those from the litter decomposing on free‐floating vegetation. Our results highlight that in wetlands, free‐floating vegetation could play a vital role in litter decomposition, which is linked to the regulation of nutrient cycling in ecosystems.     

亚热带3种树种凋落叶厚度对其分解速率及酶活性的影响

对中国亚热带树种杉木(Cunninghamia lanceolata)、香樟(Cinnamomum camphora)、银杏(Ginkgo biloba)3个树种在不同凋落物厚度下凋落物分解速率和分解酶活性进行了探究.利用分解网袋法,根据浙江省的平均酸雨水平,在酸雨(pH4.0)条件下设置了凋落物40g、凋落物20g、凋落物10g 3个梯度.结果表明:凋落物分解速率随厚度的增加呈加快的趋势,杉木凋落物10、20、40g的年分解系数K分别为0.24、0.27、0.34,香樟凋落物10、20、40g的年分解系数K分别为0.25、0.3、0.32,银杏凋落物10、20、40g的年分解系数K分别为0.42、0.5、0.58;脲酶活性表现为:凋落叶40g＞凋落叶20g＞凋落叶10g,纤维素酶活性表现为:凋落叶40g、凋落叶20g＞凋落叶10g,蔗糖酶活性表现为:后期凋落叶40g＞凋落叶20g＞凋落叶10g,凋落物分解过程是多种酶共同作用的结果.     

泰山4种优势造林树种叶片凋落物分解对凋落物内细菌群落结构的影响

为研究泰山不同造林树种凋落物叶分解对细菌群落的影响。以泰山4种主要优势造林树种刺槐(Robinia pseucdoacacia)、麻栎(Quercus acutissima)、油松(Pinus tabulaeformis)和赤松(Pinus densiflora)为研究对象,采用凋落物分解袋法及Illumina Miseq测序平台对细菌16S rDNA V4—V5区扩增产物进行双端测序,分析了4种树种叶片凋落物分解对细菌群落结构及多样性的影响。结果表明:(1)4种树种叶片分解速率差异显著(P0.05),刺槐分解速率显著高于其他3个树种(P0.05),表现为刺槐赤松油松麻栎。(2)4种叶凋落物分解一年后化学元素含量与初始化学元素相比均存在显著差异。C、木质素含量均显著降低(P0.05);N、P含量显著升高(P0.05)。(3)所有样品一共获得643440条有效序列,分属于35门,92纲,121目,246科,410属,206种。细菌群落NMDSβ-多样性分析显示除油松和赤松间差异较小外,其他树种间差异程度均较大。其中,细菌群落相对丰度在5%以上的优势类群是变形菌门、放线菌门、拟杆菌门、酸杆菌门,且在4种处理之间差异显著(PSymbol|@@0.05)。在纲水平上,α-变形菌纲、β-变形菌纲、不明放线菌纲、鞘脂杆菌纲、γ-变形菌纲、δ-变形菌纲为主要的优势纲,其中不明放线菌纲和鞘脂杆菌纲差异显著(PSymbol|@@0.05)。在种水平上,Bradyrhizobium elkanii和Luteibacter rhizovicinus在4个处理中都为优势种,每个处理也都有自己所特有的优势种。(4)4个处理细菌丰富度(OUT、观测到的物种数和ACE指数)和系统发育多样性(PD指数)之间差异显著(PSymbol|@@0.05),且阔叶树种刺槐和麻栎显著高于针叶树种赤松和油松。(5)叶片凋落物性状和细菌群落NMDS分析表明,细菌群落多样性受到凋落物化学性质的影响,尤其是凋落物初始C/N比和木质素/N比。此外,在细菌群落多样性和叶片凋落物化学性质两个因素中,分解速率与凋落物化学性质相关性更大。研究结果有助于理解细菌群落结构和多样性对森林生态系统叶片凋落物分解的影响。     

根系在凋落物层生长对凋落叶分解及酶活性的影响

根系向凋落物层生长是森林生态系统存在的普遍现象,研究根系存在对凋落物分解的影响对理解森林生态系统的养分物质循环具有重要意义.在福建三明市楠木和格氏栲林进行1年的凋落叶分解试验,设置有根处理和无根处理(对照),研究根系生长对凋落叶分解速率、养分释放和酶活性的影响.结果表明:在分解360 d后,有根处理楠木和格氏栲凋落叶干...     

毛竹凋落叶组成对叶凋落物分解的影响

毛竹混交林具有较高的生产力和较好的生态功能,可能与混合凋落物的养分归还特征有关。本研究采用凋落物分解袋法对不同混合比例毛竹凋落叶分解特征进行了为期1年的研究,共设置5个处理,分别为Ⅰ(毛竹纯叶)、Ⅱ(毛竹、楠木叶比例为8:2);Ⅲ(毛竹、杉木叶比例8:2)、Ⅳ(毛竹、楠木叶比例5:5)和Ⅴ(毛竹、杉木叶比例5:5)。结果表明,不同处理凋落物分解速率符合Olson指数分解模型,R2均高于0.92。5个处理分解系数的排列顺序为Ⅱ>Ⅰ>Ⅲ>Ⅴ>Ⅳ,分别为0.68、0.66、0.58、0.55和0.49。处理Ⅰ和Ⅱ的分解速度显著高于其他处理,说明并非所有类型毛竹混合凋落叶均会促进凋落物分解,只有合适的比例和树种会促进凋落物分解。其中,竹阔混合凋落叶的分解速度高于竹针混合凋落叶的分解速度,竹阔混交可能更有利于竹林持续生产力的维持。N、P、K3种元素养分释放模式不同,N元素表现为净富集与净释放交替出现;P元素在经过4个月的快速富集后,4—5个月有短暂的净释放过程,其后呈富集状态;K元素浓度先升高后降低,在放置的前3个月净释放,随后呈富集状态。竹林凋落叶的养分含量对凋落物养分归还有重要影响,尤其是C/N和P可能作为竹林凋落...     

科尔沁沙地植物成熟叶片性状与叶凋落物分解的关系

采用室内培养的方法,对科尔沁沙质草地20个主要植物种(10个单子叶植物种和10个双子叶植物种)叶凋落物的CO2释放量和释放速率进行比较,同时测定了20种植物成熟叶片的热值、镁浓度、磷浓度、氮浓度、钾浓度、碳浓度、碳氮比、氮磷比、比叶面积、干物质含量以及叶面积等11项叶片性状,分析20种植物叶凋落物的CO2释放量和释放速率与11项叶片性状的相关关系.结果表明, 20种植物的叶片性状在物种间变异范围很大,大多数指标的最大值和最小值的差异在3倍以上,而个别指标如叶镁浓度差异更大,接近9倍之多.由于本项研究中的20种植物均来自于同一样地,因此认为20种植物的自身性状和遗传特性决定了其叶片性状的变异.20种植物叶凋落物培养28d的CO2释放量平均值为(4121±1713)μg kg-1,释放量最大的是尖头叶藜(8767±177)μg kg-1干土,释放量最小的是马唐(1669±47)μg kg-1,二者相差5倍以上.但20种植物叶凋落物CO2释放速率表现相同的变化趋势,培养初期凋落物分解迅速,后期分解相对缓慢.比较分析发现,双子叶植物和单子叶植物叶凋落物CO2释放量、CO2释放速率,以及成熟叶片的叶氮浓度、叶碳浓度、叶C/N和叶干物质含量之间差异显著.相关分析揭示,20种植物成熟叶片叶氮浓度、叶碳浓度、叶C/N和叶干物质含量与叶凋落物分解过程中的CO2释放量和释放速率之间呈显著的相关关系,说明可以利用成熟叶片的N浓度、C浓度、C/N以及干物质含量间接的预测叶凋落物的分解速率.     

Evaluation of macrofaunal effects on leaf litter breakdown rates in aquatic and terrestrial habitats

Abstract Decomposition of the organic matter is a key process in the functioning of aquatic and terrestrial ecosystems, although different factors influence processing rates between and within these habitats. Most patterns were described for temperate regions, with fewer studies in tropical, warmer sites. In this study, we carried out a factorial experiment to compare processing rates of mixed species of leaf litter between terrestrial and aquatic habitats at a tropical site, using ?ne and coarse mesh cages to allow or prevent colonization by macroinvertebrates. The experiment was followed for 10 weeks, and loss of leaf litter mass through time was evaluated using exponential models. We found no interaction between habitat and mesh size and leaf litter breakdown rates did not differ between ?ne and coarse mesh cages, suggesting that macroinvertebrates do not influence leaf litter decomposition in either habitat at our studied site. Leaf breakdown rates were faster in aquatic than in terrestrial habitats and the magnitude of these differences were comparable to studies in temperate regions, suggesting that equivalent factors can influence between‐habitat differences detected in our study.     

Cellulase activity on decomposing leaf litter in microcosms

In this paper, we describe cellulase and cellobiose dehydrogenase (CBDH) dynamics in relation to incubation time, mass loss and chemical composition of decomposing deciduous leaf litter. Cellulose disappearance from litter coincided with periods of maximum cellulase activity. CBDH activity peaked later in decomposition after cellulase activity had declined. Enzyme activity patterns differed among litter types when expressed on the basis of decomposition time or cumulative mass loss. The patterns converged when expressed on the basis of chemical composition as indexed by the fraction of cellulose in the lignocellulose complex. We present a three-stage model of decomposition based on temporal changes in cellulase activities and coincident changes in litter chemical composition.     

落叶收集法测定叶面积指数的快速取样方法

叶面积指数(LAI)是植被冠层结构的一个重要参数,它不仅是许多生态和气候模型的重要输入变量,而且是生态系统动态变化监测的一个重要指标。LAI可通过各种间接和直接的手段来观测,而间接观测的LAI值常常需要直接的观测数据来校验。落叶收集法是一种广泛使用的直接观测LAI的方法,过去的研究还未发现有涉及落叶收集的取样技术及其观测精度的内容。对长白山和北京地区落叶阔叶林的落叶进行了3a的观测,每年一次性收集落叶样品分析,研究结果表明:①不同层次落叶的含水量差异巨大,且落叶含水量的日变化明显。上下层落叶的含水量绝对值差异高达10%以上,日变化绝对值差异高达20%以上。因此,在野外收集落叶样本时,为减小落叶含水量变化所导致的LAI观测误差,应从上到下直到地面进行取样,且尽可能多地收集落叶样本。②在落叶阔叶人工林和天然林里,无论样地的大小(1hm2或30m×30m样地),无论取样单元的大小(1m2或25m2分辨率),林内的LAI分布很不均匀,LAI介于0-15.5(1m2分辨率的1hm2样地)或者2.6-9.1(25m2分辨率的30m×30m样地)。③要准确测定落叶林的LAI,收集落叶的样地面积越大越好,且尽量选择地势平坦的样地。对于1hm2或者30m×30m大小的样地,可随机布设一个10m×10m的小样地来观测,精度分别可达85%、80%。④10m×10m小样地的LAI观测,可将其分为4个相邻的5m×5m小样进行取样。对每个5m×5m小样,快速的取样方法是:Ⅰ.随机布设6个1m2取样,这样取样可以保证在99%概率水平上,100m2、30m×30m和1hm2样地的LAI观测精度分别为90%、75%、70%左右。Ⅱ.随机布设11个1m2取样。可以保证在99%概率水平上,100m2、30m×30m和1hm2样地的LAI观测精度分别为94%、80%、75%左右。     

Cave invertebrate assemblages differ between native and exotic leaf litter

Abstract Allochtonous leaf litter is an important source of energy and nutrients for invertebrates in cave ecosystems. A change to the quality or quantity of litter entering caves has the potential to disrupt the structure and function of cave communities. In this study, we adopted an experimental approach to examine rates of leaf litter decomposition and the invertebrate assemblages colonizing native and exotic leaf litter in limestone caves in the Jenolan Caves Karst Conservation Reserve, New South Wales, Australia. We deployed traps containing leaf litter from exotic sycamore (Acer pseudoplatanus) and radiata pine (Pinus radiata) trees and native eucalypts (Eucalyptus spp.) in twilight zones (near the cave entrance) and areas deep within the caves for 3 months. Thirty‐two invertebrate morphospecies were recorded from the litter traps, with greater richness and abundance evident in the samples from the twilight zone compared with areas deep within the cave. Sycamore litter had significantly greater richness and abundance of invertebrates compared with eucalypt and pine litter in samples from the twilight zone, but there was no difference in richness or abundance among litter samples placed deep within the cave. Relative rates of decay of the three litters were sycamore > eucalypt > pine. We discuss the potential for the higher decomposition rates and specific leaf area in sycamores to explain their higher invertebrate diversity and abundance. Our findings have important implications for the management of exotic plants and the contribution of their leaf litter to subterranean ecosystems.     

Community composition and diversity of riparian forests regulate decomposition of leaf litter in stream ecosystems

Riparian forest plantings are a well‐established restoration technique commonly used to stabilize banks and intercept nutrient flow from adjacent agricultural fields. Tree species planted for these efforts may not reflect mature forest communities within the same region. Given contemporary research on links between biodiversity and ecosystem functioning, we conducted a leaf‐litter decomposition study to investigate how mixing of detrital resources that reflect forest community composition would regulate in‐stream leaf litter. Leaf litter bags containing material from a mature forest (Liriodendron tulipifera, Acer rubrum, Quercus rubra, full factorial treatments = 7) and a restored riparian forest (Cornus sericea, Fraxinus pennsylvanica, Platanus occidentalis, full factorial treatments = 7) were deployed in a stream reach that experienced riparian reforestation in 2004. Litter from the restored riparian community had less mass remaining (45.28 ± 2.27%) than that from the mature riparian community (54.95 ± 2.19%) after 5 weeks. In addition, mixed litter treatments in the restored riparian community had less mass remaining (40.54 ± 2.37%) than single‐species treatments (51.80 ± 4.05%), a pattern not observed in the mature forest community. Results highlight the importance of planting mixed‐species assemblages as this structure may regulate processes such as decomposition and food‐web structure, processes often not targeted in the restoration plans.     

A fungal endophyte slows litter decomposition in streams

1. Phyllosphere interactions are known to influence a variety of tree canopy community members, but less frequently have they been shown to affect processes across ecosystem boundaries. Here, we show that a fungal endophyte (Rhytisma punctatum) slows leaf litter decomposition of a dominant riparian tree species (Acer macrophyllum) in an adjacent stream ecosystem. 2. Patches of leaf tissue infected by R. punctatum show significantly slower decomposition compared to both nearby uninfected tissue from the same leaf, and completely uninfected leaves. These reduced rates of decomposition existed despite 50% greater nitrogen in infected tissues and may be driven by slower rates of decomposition for fungal tissues themselves or by endophyte–hyphomycete interactions. 3. Across a temperate forest in the Pacific Northwest, approximately 72% of all A. macrophyllum leaves were infected by R. punctatum. Since R. punctatum infection can influence leaf tissue on entire trees and large quantities of leaf litter at the landscape scale, this infection could potentially result in a mosaic of ‘cold spots’ of litter decomposition and altered nutrient cycling in riparian zones where this infection is prevalent.     

Macroinvertebrate identity mediates the effects of litter quality and microbial conditioning on leaf litter recycling in temperate streams

Plant litter decomposition is an essential ecosystem function that contributes to carbon and nutrient cycling in streams. Aquatic shredders, mainly macroinvertebrates, can affect this process in various ways; they consume leaf litter, breaking it down into fragments and creating suitable habitats or resources for other organisms through the production of fine particulate organic matter (FPOM). However, measures of litter‐feeding traits across a wide range of aquatic macroinvertebrates are still rare. Here, we assessed the contributions of 11 species of freshwater macroinvertebrates to litter decomposition, by measuring consumption rate, FPOM production, and assimilation rate of highly decomposable (Alnus glutinosa) or poorly decomposable (Quercus robur) leaf litter types. In general, an increase in the quality of litter improved the litter consumption rate, and fungal conditioning of the leaf litter increased both the litter consumption rate and FPOM production. Macroinvertebrates specializing in leaf litter consumption also appeared to be the most sensitive to shifts in litter quality and the conditioning process. Contrary to expectations, the conditioning process did not increase the assimilation of low‐quality litter. There was a strong correlation between the relative consumption rate (RCR) of the two litter types, and the relative FPOM production (RFP) was strongly correlated to the RCR. These findings suggest a consistent relationship between RCR and macroinvertebrate identity that is not affected by litter quality, and that the RFP could be inferred from the RCR. The varying responses of the macroinvertebrate feeding traits to litter quality and the conditioning process suggest that the replacement of a shredder invertebrate species by another species could have major consequences for the decomposition process and the detritus‐based food web in streams. Further studies onto the importance of invertebrate identity and the effects of litter quality in a variety of freshwater ecosystems are needed to understand the whole ecosystem functioning and to predict its response to environmental changes.