基于栖息地斑块尺度的青弋江河源溪流鱼类群落的时空格局

确定鱼类的栖息地利用格局是研究物种与环境关系的基础, 也是鱼类多样性保护和管理的必要前提。目前, 有关溪流鱼类群落的栖息地斑块利用格局尚存在争议。基于2012年9月至2013年8月对青弋江河源溪流的逐月调查数据, 初步研究了鱼类群落的栖息地斑块利用格局, 着重在栖息地斑块尺度上解析了鱼类群落的时空变化规律。主要研究结果显示, 深潭和急滩2类斑块间的底质、流速、水深、溶氧栖息地因子显著差异, 且深潭斑块的环境稳定性高于急滩。研究共采集鱼类15种, 其中鲤科鱼类8种, 占采集物种数50%以上。基于鱼类物种存在与否的不连续变量的分析结果显示, 鱼类物种组成的斑块间和月份间变化均不具显著性。但是, 基于鱼类物种多度的连续变量的分析结果显示, 鱼类群落结构存在有显著的斑块间变化和时间动态; 就斑块间变化而言, 原缨口鳅(Vanmanenia stenosoma)在急滩斑块中的多度更高, 而宽鳍 (Zacco platypus)、光唇鱼(Acrossocheilus fasciatus)和尖头 (Phoxinus oxycephalus)等其他关键物种则在深潭中具有更高多度。深潭斑块的鱼类物种数显著高于急滩, 但2类斑块间的个体数无显著差异。深潭斑块的鱼类物种数较稳定, 而个体数月变化显著, 可能与鱼类繁殖和群体补充以及越冬死亡等有关; 急滩鱼类物种数和个体数的月变化均显著, 除了与鱼类群体补充和越冬死亡有关以外, 还可能受越冬时栖息地斑块选择变化的影响。上述结果表明, 在栖息地斑块空间尺度上, 由于研究区域内大多数物种在栖息地斑块选择上无明显的特化性, 深潭和急滩斑块间鱼类的物种组成分布不符合前人所报道的生境-共位群格局, 但区域内常见种多度的变化可引起鱼类群落结构的斑块间差异和季节动态。       

高山森林溪流冬季不同时期凋落物分解中水溶性氮和磷的动态特征

为了解高山森林溪流凋落物冬季分解过程中水溶性氮和磷的变化过程,采用凋落叶分解袋法,以川西高山森林典型乔木(四川红杉、方枝柏)和灌木(高山杜鹃、康定柳)凋落叶为研究对象,研究冬季不同时期(冻结初期、冻结期、融化期)溪流、河流、河岸带以及林下凋落叶水溶性氮和磷的动态特征.结果表明:经过一个冬季的分解,4种凋落物在不同生境下各时期的水溶性氮含量无显著变化.水溶性磷含量除林下外在其他生境均显著降低,表现出河流＜溪流＜河岸带＜林下的规律.高山森林凋落叶分解过程中水溶性磷含量与平均温度、正积温、负积温和流速呈显著负相关,水溶性氮含量与正积温呈显著正相关,物种显著影响凋落物分解过程中水溶性氮和磷的含量.高山森林凋落物冬季分解过程中水溶性磷更易随河流和溪流等水体的流动而流失,而水溶性氮受冬季水环境的影响相对较小.     

雪被斑块对川西高山森林凋落叶N和P释放的影响

采用凋落物网袋法,研究冬季不同关键时期雪被斑块对川西高山森林6种代表性树种凋落物分解过程中N和P释放的影响.结果表明: 整个雪被覆盖季节凋落物N表现为富集,P表现为释放,且雪被融化期P释放速率最大.厚型和中型雪被斑块下凋落物P释放速率大于薄型和无雪被斑块,而薄型和无雪被斑块下凋落物的N释放速率明显较高.6种凋落物N释放率和释放速率与日均温呈显著负相关;除岷江冷杉外,其他树种凋落物P释放率和释放速率与日均温表现为正相关.气候变暖情景下冬季雪被覆盖的减小将促进高山森林冬季凋落物分解过程中N释放,抑制P释放.     

雪被斑块对川西亚高山森林凋落物冬季分解过程中钾和钠动态的影响

亚高山森林冬季不同厚度雪被斑块下显著的冻融格局差异可能对凋落物分解过程中钾(K)和钠(Na)的动态具有重要影响, 然而已有研究还不足以清晰地认识这一过程。以川西亚高山森林6种代表性树种凋落物为研究对象, 采用凋落物网袋法, 探讨冬季不同厚度雪被斑块下雪被形成期、覆盖期和融化期凋落物分解过程中K和Na元素释放或富集的特征。整个雪被覆盖时期, 6种凋落物分解过程中Na均表现为富集特征, 且以覆盖期最为明显; 而K表现为释放特征, 以雪被融化期释放率最大。相对于其他雪被斑块, 厚型和中型雪被斑块下凋落物K释放率相对较高; 除康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)外, 其他物种凋落物在厚型和中型雪被斑块下Na富集率较高。同时, 统计分析结果表明, 物种和雪被显著影响冬季不同关键时期凋落物K和Na元素动态。除红桦(Betula albosinensis)和方枝柏(Sabina saltuaria)凋落物外, 温度因子与凋落物K和Na动态变化呈显著正相关。这些结果表明气候变暖情景下冬季雪被覆盖的减小将抑制亚高山森林冬季凋落物分解过程中K和Na元素的释放, 但是释放程度受凋落物质量和雪被覆盖时期的显著影响。     

Effects of snow patch on the dynamics of potassium and sodium during litter decomposition in winter in a subalpine forest of western Sichuan

亚高山森林冬季不同厚度雪被斑块下显著的冻融格局差异可能对凋落物分解过程中钾(K)和钠(Na)的动态具有重要影响, 然而已有研究还不足以清晰地认识这一过程。以川西亚高山森林6种代表性树种凋落物为研究对象, 采用凋落物网袋法, 探讨冬季不同厚度雪被斑块下雪被形成期、覆盖期和融化期凋落物分解过程中K和Na元素释放或富集的特征。整个雪被覆盖时期, 6种凋落物分解过程中Na均表现为富集特征, 且以覆盖期最为明显; 而K表现为释放特征, 以雪被融化期释放率最大。相对于其他雪被斑块, 厚型和中型雪被斑块下凋落物K释放率相对较高; 除康定柳(Salix paraplesia)和高山杜鹃(Rhododendron lapponicum)外, 其他物种凋落物在厚型和中型雪被斑块下Na富集率较高。同时, 统计分析结果表明, 物种和雪被显著影响冬季不同关键时期凋落物K和Na元素动态。除红桦(Betula albosinensis)和方枝柏(Sabina saltuaria)凋落物外, 温度因子与凋落物K和Na动态变化呈显著正相关。这些结果表明气候变暖情景下冬季雪被覆盖的减小将抑制亚高山森林冬季凋落物分解过程中K和Na元素的释放, 但是释放程度受凋落物质量和雪被覆盖时期的显著影响。     

雪被覆盖对高山森林凋落物分解过程中水溶性和有机溶性组分含量的影响

季节性雪被可能通过冻结、淋溶以及冻融循环等对高山森林凋落物水溶性和有机溶性组分含量产生影响.本文采用凋落物分解袋法,以川西高山森林典型乔木（四川红杉、岷江冷杉、红桦、方枝柏）和灌木（高山杜鹃、康定柳）凋落物为研究对象,研究了雪被覆盖不同时期（雪被形成期、雪被覆盖期和雪被融化期）和雪被厚度（厚型雪被、中型雪被、薄型雪被和无雪被）下凋落物水溶性和有机溶性组分含量的动态变化特征.结果表明： 在一个冬季的分解过程中,6种凋落物水溶性组分含量在雪被形成期和融化期降低而雪被覆盖期增加,但除高山杜鹃凋落物有机溶性组分含量在雪被覆盖期增加外,其他5种凋落物有机溶性组分含量在整个冬季呈降低趋势.相对于凋落物有机溶性组分含量,不同厚度雪被斑块对凋落物水溶性组分含量变化的影响更大,且主要表现在雪被形成期和雪被覆盖期.相对于其他雪被斑块,薄型雪被斑块更加显著地促进了高山柳和高山杜鹃凋落物水溶性组分含量降低,但显著抑制了方枝柏凋落物水溶性组分含量降低,而其他凋落物水溶性组分含量变化在不同斑块间无显著差异.冬季高山森林雪被对凋落物水溶性和有机溶性组分含量的影响主要受控于凋落物质量.     

长白山白桦(Betula platyphlla)纯林和白桦山杨 (Populus davidiana)混交林凋落物的分解

采用交互分解实验,研究长白山白桦叶片和白桦、山杨与水曲柳混合叶片在白桦纯林和白桦山杨混交林内的分解过程。两年的分解实验结果表明,两种类型叶片均存在一个快速分解阶段和一个慢速分解阶段,森林类型和凋落物类型对凋落物分解率的影响在快速分解阶段不显著而在慢速分解阶段显著;混交林内的环境促进了凋落物分解和养分元素释放;在同一林型内,底物质量高的混合叶片其分解率和养分元素释放率均大于底物质量低的白桦叶片;凋落物的底物质量在一定程度上可以抵消森林类型对凋落物分解的影响;白桦山杨混交林混合叶片分解速率和养分元素释放率要显著大于白桦纯林内的白桦叶片,说明白桦山杨混交林的物质循环速度和养分元素供应能力要显著大于白桦纯林。     

长白山白桦(Betula platyphlla)纯林和白桦山杨 (Populus davidiana)混交林凋落物的分解

采用交互分解实验,研究长白山白桦叶片和白桦、山杨与水曲柳混合叶片在白桦纯林和白桦山杨混交林内的分解过程。两年的分解实验结果表明,两种类型叶片均存在一个快速分解阶段和一个慢速分解阶段,森林类型和凋落物类型对凋落物分解率的影响在快速分解阶段不显著而在慢速分解阶段显著;混交林内的环境促进了凋落物分解和养分元素释放;在同一林型内,底物质量高的混合叶片其分解率和养分元素释放率均大于底物质量低的白桦叶片;凋落物的底物质量在一定程度上可以抵消森林类型对凋落物分解的影响;白桦山杨混交林混合叶片分解速率和养分元素释放率要显著大于白桦纯林内的白桦叶片,说明白桦山杨混交林的物质循环速度和养分元素供应能力要显著大于白桦纯林。     

底栖分解类群对金佛山森林溪流凋落物混合分解的影响

凋落物分解对于维持源头溪流生态系统碳和养分平衡有重要意义。以亚热带典型源头溪流金佛山溪流为代表,选取3种河岸带常见凋落叶为分解对象,设计3个单种和4个混合物种的凋落物组合,在原位放置3种孔径的分解袋（0.05mm、0.25mm和2mm）,探讨混合凋落物的性状与底栖分解类群对叶片质量损失和混合效应的影响。结果表明：（1）微生物在凋落物分解过程中相对贡献均大于50%,小型和大型底栖动物进一步加速了凋落物的分解过程。（2）单种凋落物分解速率存在显著差异：八角枫（Alangium chinense,质量损失率为53.05%）>缺萼枫香（Liquidambar acalycina,30.00%）>薄叶润楠（Machilus leptophylla,12.63%）。（3）混合凋落物中仅微生物参与的处理均表现为负的非加和效应,其中八角枫+缺萼枫香、八角枫+薄叶润楠、八角枫+缺萼枫香+薄叶润楠三个处理的效应显著;小型底栖动物加入后均表现为正的非加和效应,但不显著;在微生物、小型和大型底栖动物的共同作用下,缺萼枫香+薄叶润楠和八角枫+缺萼枫香+薄叶润楠的两个处理的正的非加和效应显著。亚热带源头溪流中凋落物分解功能与河岸植物和分解者类群的复杂性密切相关。     

不同林龄尾巨桉人工林凋落物和土壤C、N、P化学计量特征

为正确认识桉树(Eucalyptus spp.)人工林凋落物和土壤C、N、P时空分配格局及两者间的关系,对5个林龄尾巨桉林分凋落物及土壤C、N、P含量及化学计量比进行测定分析。结果表明,凋落物的C含量均显著大于土壤,且不同林龄间凋落物C含量无显著差异,1年生人工林土壤表层(0~20 cm)的C含量显著小于3~7年生,其他土层C含量在不同林龄间差异不显著。凋落物的N含量均显著高于土壤,且1年生人工林显著大于其他林龄的,而土壤表层的N含量以7年生人工林最大,1年生的最小。凋落物的P含量除1年生人工林显著大于3年生外,其他林龄间均无显著差异,土壤的P含量在不同林龄间的差异均不显著。凋落物C∶N随林龄呈逐渐增大趋势,且显著大于土壤层。凋落物的C∶P和N∶P在不同林龄间的差异不显著,但均显著大于土壤层。凋落物的N含量与表层土壤的C、N含量呈极显著负相关,凋落物的C∶N与表层土壤的C∶P,N∶P呈显著正相关,表层土壤C、N积累受到凋落物N的制约。因此,在桉树人工林经营管理过程中如何降低凋落物分解的N限制性、提高养分传递效率及合理施肥显得十分重要。     

Across-reach consistency in macroinvertebrate distributions among litter patch types in Japanese headwater streams

Different types of litter patches with contrasting macroinvertebrate assemblages have been observed within a stream reach. This study examined whether distributions of macroinvertebrates among three litter patch types (riffle, middle, edge) were consistent between reaches with different channel characteristics in headwater streams in central Japan. Mass of leaves per unit area was significantly higher in riffle and edge patches than in middle patches, which was consistent between reaches, while no consistent pattern was evident between reaches for mass of either woody material or small litter fragments. Distribution among the patch types was consistent between reaches for 11 out of 13 dominant macroinvertebrate taxa; density was highest in riffle patches for 5 taxa and in middle patches for 5 taxa. Although we previously related densities of some taxa to mass of woody material or small litter fragments, hydraulic characteristics (water depth, current velocity), which were consistent between reaches, may be more important determinants of macroinvertebrate distributions among the patch types, even within pools (i.e. middle and edge patches) where current is uniformly low. The results of this study indicate that a reach-scale macroinvertebrate community structure associated with litter is likely to vary according to litter patch type composition, which would be affected by channel characteristics of the reaches.     

Impact of highway construction on leaf processing in aquatic habitats of eastern Tennessee

Rates of leaf litter processing at eight sites were used in conjunction with other methods to evaluate the impact of highway construction on aquatic habitats. Monthly processing of white oak leaves from four different mesh size bags at unimpacted reference sites indicated that the three larger mesh sizes were useful for comparing sites, as they did not restrict invertebrate colonization and provided similar rates of processing within sites. Small mesh size (0.12 mm) prevented leaf shredding macroinvertebrates from colonizing bags, and caused significantly slower leaf processing in a riffle.Leaf processing was fastest in a reference riffle above an area of highway construction but was significantly slower in the reference pool due to low current velocity and the absence of shredders. Leaf processing in a riffle below the highway was slower than the reference riffle, and the number of shredders was reduced. Removal of streamside vegetation during highway construction caused increased stream temperatures and reduced the amount of natural leaf accumulations, thereby reducing shredder habitat. At other sites highway construction caused less of an impact than preexisting environmental influences. Leaf processing in an riffle of a lower pH stream was significantly slower than in the reference riffle. Shredders were absent from the low pH stream, and rates of leaf processing in the acid impacted riffle and pool were similar to those of the reference pool. Comparisons of the low pH stream with the reference stream indicated that physical processes were less important than biological processes of leaf decay. Leaf processing in ponds was similar to that of stream pools. Processing was faster in a small versus large pond, and a high density of invertebrates was associated with leaf bags in the small pond after one year.     

Influence of urban tributaries on freshwater mussel populations in a biologically diverse piedmont (USA) stream

We investigated the distribution patterns of senescent and green leaf litter patches on a streambed to evaluate the hypothesis that the different immersion times of senescent leaves in long-term benthic storage and newly retained green leaves affect streambed distribution patterns in summer (June, July, and August). We counted all the leaf litter patches in the streambed of the study reach, comparing the physical condition of patches and classifying the trapping obstacles associated with each patch type. The distribution patterns of senescent and green leaf litter patches differed. Green leaf litter patches were more numerous at every sampling date, with most trapped by cobbles, whereas senescent leaf litter patches were retained by twig obstacles, backwaters, and cobbles. In June and July, senescent leaf litter patches were located in significantly deeper stream areas than were green leaf litter patches. The distribution of senescent leaves would be primarily determined during spring snowmelt-driven floods. We speculate that senescent leaves were originally located at the edges of pools in the main flow pathway of the channel, which overflowed in the floods. We conducted flume experiments to clarify the transport characteristics of senescent and green painted maple and manchurian alder leaves in the water column. Our hypothesis was that the transport characteristics of each leaf type differ when they first enter the water, because of differing leaf properties. The flume experiments showed that duration of surface flotation differed for senescent and green leaves and for the two tree species. These differences in the duration of leaves on the streambed and in the floating time of green leaves of different trees ensure varied food resources for macroinvertebrates in various physical conditions. Handling editor: B. Oertli     

Disappearance of overstorey and understorey litter in an open eucalypt forest

Litter accumulation dynamics and first year rates of disappearance were investigated for leaves of overstorey and understorey species in the mixed eucalypt forest in the Griffith University study area, Queensland, Australia. The average biomass of the litter layer, was 10.2 t/ha. The wood and overstorey leaf litter formed 62.7% of the accumulated litter biomass, and were spread continuously across the ground. The distribution of shrub litter was discontinuous, being concentrated in localized patches beneath individual plants. The litter bag and tethered leaf techniques were used to measure the rate of disappearance of overstorey and shrub leaves. The ‘pairedquadrat’ technique was used to measure the weight loss of the grasses. The small leaves of the dominant shrub, Pultenaea villosa Willd. disappeared most rapidly, followed by the overstorey leaves, grasses and Acacia leaves. Fragmentation by physical factors and litter fauna appeared to be the major factors responsible for the disappearance of the overstorey leaves during the first year of exposure. The data suggest that removal of leaf constituents by leaching and microbial decomposition were more important for the shrub litter than the overstorey leaves. Fractional disappearance rates (loss constants) obtained from the short term weight loss measurements, and calculated using the steady-state model of litter accumulation (k=L/X), overestimated the rate of litter disappearance and litter decomposition. For the overstorey leaves in particular, the loss constants also overestimated the rate of loss of material from the litter layer since the fragmented and consumed tissues accumulated in the fraction of comminuted fragments before moving into the humus/soil subsystem. A compartment model of the components of the litter layer in the mixed eucalypt forest is presented. It incorporates overstorey and understorey litter accession, accumulation and disappearance data. The adoption of a two dimensional decomposition/accumulation matrix is suggested as an appropriate framework within which to simulate the dynamics of the litter subsystem in mixed eucalypt forest ecosystems.     

Differences in patches of retention among leaves,woods and small litter particles in a headwater stream: the importance of particle morphology

The location of retention in the channel can influence invertebrate assemblage and breakdown processes associated with a litter particle in heterogeneous streams. We previously identified four types of litter patches that formed on riffles or different locations in pools (middle, edge, alcove), and demonstrated that middle patches had higher litter processing rates than the other patches. In this study, we examined differences in retention on the four patch types among leaves, woody materials and small litter particles, and among leaves of different sizes, by sampling natural and manipulated litter particles that were newly retained. Proportionally more woody materials, leaf pieces (16–50 mm) and particulate organic matter (1–16 mm) than leaves (>50 mm) were retained on middle patches, while proportionally more leaves than the other litter particles were retained on riffle and edge patches. The retention pattern of leaf species with different leaf sizes and a released experiment of leaf particles revealed that proportionally more leaf particles with smaller sizes were retained on middle patches. The flexibility, shape and dryness of litter particles also seem to affect the location of retention in the channel. These results suggest that the morphology of litter particles have the potential to affect the biological use and breakdown of litter particles through determining the location of retention within the channel. The size of leaves and processes that alter leaf size may have important roles on the breakdown and utilisation by invertebrates in these heterogeneous streams.     

Limited evidence that mixing leaf litter accelerates decomposition or increases diversity of decomposers in streams of eastern Canada

Most studies of terrestrial litter decomposition in streams and rivers have used leaves from a single tree species, but leaf packs in streams in eastern North America are usually mixtures of two or more species. Litter mixtures may decay more quickly than either of the component species. If so, estimates of stream energy and nutrient budgets may be inaccurate. In northern Nova Scotia, Canada, we measured mass loss from binary mixtures (1:1 mass ratio) of leaf litter in mesh bags, using freshly fallen or air-dried litter from five species of canopy trees. We repeated the experiment eight times, in summer and fall, in two streams and a small river, over 3 years. In some trials we enumerated benthic invertebrate and fungal colonization of decaying litter. Although there were marked differences in mass loss rates among litter types, decomposition was accelerated in mixtures relative to the mean of the component species in only three of eight trials, and only in mixtures containing N-rich speckled alder leaves. Mixing yellow birch and red maple leaves inhibited decomposition. Diversity (Shannon–Weaver Index), species richness, and abundance of aquatic hyphomycete fungi, as indexed by conidial production, were never greater (and sometimes less) on litter mixtures than on the component species. Total numbers, taxonomic richness and diversity of benthic invertebrates generally, and litter-feeding species in particular, were not augmented by mixing litter types. Litter mixtures appear to dilute a preferred substrate with patches of a less preferred substrate. Our results provide only weak support for the contention that combining two litter types leads to acceleration of decomposition rates. Handling editor: K. Martens     

Flow-substrate interactions create and mediate leaf litter resource patches in streams

1. The roles that streambed geometry, channel morphology, and water velocity play in the retention and subsequent breakdown of leaf litter in small streams were examined by conducting a series of field and laboratory experiments. 2. In the first experiment, conditioned red alder (Alnus rubra Bongard) leaves were released individually in three riffles and three pools in a second‐order stream. The transport distance of each leaf was measured. Several channel and streambed variables were measured at each leaf settlement location and compared with a similar number of measurements taken at regular intervals along streambed transects (‘reference locations’). Channel features (such as water depth) and substrate variables (including stone height, stone height‐to‐width ratio, and relative protrusion) were the most important factors in leaf retention. 3. In the second experiment, the role of settlement location and reach type in determining the rate of leaf litter breakdown was examined by placing individual conditioned red alder leaves in exposed and sheltered locations (on the upper and lower edges of the upstream face of streambed stones, respectively) in riffle and pool habitats. After 10 days, percent mass remaining of each leaf was measured. Generally, leaves broke down faster in pools than in riffles. However, the role of exposure in breakdown rate differed between reach types (exposed pool > sheltered pool > sheltered riffle > exposed riffle). 4. In the third experiment, the importance of substrate geometry on leaf litter retention was examined by individually releasing artificial leaves upstream of a series of substrate models of varying shape. Substrates with high‐angle upstream faces (were vertical or close to vertical), and that had high aspect ratios (were tall relative to their width), retained leaves more effectively. 5. These results show that streambed morphology is an important factor in leaf litter retention and breakdown. Interactions between substrate and flow characteristics lead to the creation of detrital resource patchiness, and may partition leaf litter inputs between riffles and pools in streams at baseflow conditions.     

Leaf litter patches in stream create overwintering habitats for Ezo brown frog (<Emphasis Type="Italic">Rana pirica</Emphasis>)

Only fragments are known about the functions of leaf litter patches in streams for terrestrial organisms. We investigated the movement patterns of Ezo brown frogs (Rana pirica) on two occasions, in autumn 2014 and summer 2015, and the occurrence of frogs in rivers and along riverbanks on three occasions from summer to autumn 2014 along a 1.5-km stream segment that flows through the Bekanbeushi wetland, northern Japan. Ezo brown frog movement was biased toward the river channel in late autumn and this movement pattern coincided with relatively abundant Ezo brown frogs on the riverbed from autumn to winter 2014. The distribution shift was also supported by decreasing abundance of Ezo brown frogs on riverbanks from autumn to winter (no sighting in winter) during daytime observations. The abundance of overwintering Ezo brown frogs in the channel was associated most positively with leaf litter dry mass and depth, with flow velocity being relatively less important at the quadrat scale (0.063 m²). Our results demonstrated that Ezo brown frogs overwinter in the stream and suggest that leaf litter patches positively affect the quality of the overwintering habitat.     

Decomposition of litter in sub-alpine forests of Eucalyptus delegatensis,E. pauciflora and E. dives

The rate of decomposition of summer leaf-fall (abscised leaves), winter leaf-fall (containing some green leaves) and mature green (picked) leaves was assessed in sub-alpine forests of E. delegatensis (R. T. Baker), E. pauciflora (Sieb. ex Spreng) and E. dives (Schau.) in the Brindabella Range, Australian Capital Territory, using litter bag and tethered leaf techniques. The relative contribution of leaching, microbial respiration and grazing by invertebrate macrofauna to loss of leaf weight was determined. The effect of leaching and microbial respiration was assessed in terms of weight loss per unit area of leaf (specific leaf weight), while losses due to macro-faunal grazing were assessed by measuring reductions in leaf area. Litter decomposition constants for litter components (leaf, bark, wood) and total litter were determined from long-term records of litterfall and accumulated litter. Weight losses of abscised leaves during the initial 12 months ranged from 25% for E. pauciflora to 39% for E. delegatensis and were almost entirely due to reduction in specific leaf weight. Losses in the weight of leaves falling in winter ranged from 38 to 49%, while green leaves lost 45 - 59%. Approximately 50% of the total weight loss of green leaves was due to a loss in leaf area caused by skeletonization by litter macrofauna. Thus abscised leaves rather than green leaves must be used for measuring litter decomposition rates since abscised leaves constitute most of the litterfall in eucalypt forests. Leaves placed in the field in autumn decomposed slowly during the first summer, while the rate increased during the second winter and summer. Low litter moisture content appears to limit decomposition in the initial summer period in all communities, after which litterfall provides a mulch which reduces the rate of desiccation of lower litter layers. A simple linear regression model relating decomposition rate to the number of days (D) when litter moisture content exceeded 60% ODW accounted for 63-83% of the variation in decomposition of leaves in the field. Inclusion of mean monthly air temperature (T) and the product of D and T (day degrees when litter was wet) in a multiple linear regression increased the variation in decomposition accounted for to 80 – 90%. The rate of weight loss showed a positive linear relationship with the initial concentration of nitrogen (N) or phosphorus (P) in the leaf. These concentrations are an index of the decomposability of leaf substrates (e.g. degree of sclerophylly or lignification). The rate of loss of specific weight was similar for tethered leaves and for leaves enclosed in mesh bags. Measured loss in specific leaf weight after 70 – 90 weeks was less than that predicted using decomposition constants (k).     

Hot spots of leaf breakdown within a headwater stream reach: comparing breakdown rates among litter patch types with different macroinvertebrate assemblages

1. Detecting hot spots of litter decomposition will promote understanding of litter processing in a heterogeneous system. To identify hot spots of leaf breakdown within a headwater stream reach, we examined the difference in leaf breakdown rate among four types of litter patches, one that formed in riffles and three that formed in pools (middle, alcove, edge), in different seasons. 2. Middle patches showed the highest breakdown rate in some seasons; the rate in middle patches was 1.5–4 times higher than in the other patches. Thus middle patches can be regarded as hot spots of leaf breakdown in the study reach. This result contrasted with other studies showing higher breakdown rate in riffles than in pools. 3. Significant relationships between abundance of caddisfly shredders and breakdown rate were observed in seasons when the rate differed among patch types. Greater abundance of Lepidostoma seems to be responsible for middle patches being hot spots of leaf breakdown. 4. It is expected that when the proportion of leaves retained in middle patches within a reach is higher, the breakdown rate of the entire reach will be increased. Clarifying how the proportion of leaves retained on middle patches within a reach varies temporally and spatially would improve our understanding of leaf breakdown in headwater streams.