粤北地区溪流中的树叶分解及大型底栖动物功能摄食群

利用2种孔径(5mm的塑料网袋和0.1mm的布袋)的分解网袋对2种树叶在广东北部的横石水河的3级溪流中,进行了为期101d的树叶分解研究.结果表明:人面子树叶在网袋和布袋中的分解速率分别为0.0247d-1和0.0151d-1;而蒲桃树叶的分解速率则分别为0.0108d-1和0.0095d-1.说明2种树叶在布袋中的分解速率均比网袋慢,且人面子树叶的分解速率比蒲桃树叶快.定殖在2种树叶网袋中的功能摄食群以刮食者的比例最高(36%),其次是集食者(33%)和捕食者(25%),撕食者的比例最低(6%).在实验中后期,人面子树叶上的底栖动物个体总数、优势类群数和密度显著高于蒲桃树叶.说明在亚热带地区的中等级别的溪流中,由于撕食者种类减少,刮食者的类群数及密度对树叶分解速率具有显著影响.对微生物活动的抑制作用和对底栖动物取食的驱避作用使富含单宁成分的蒲桃树叶的分解速率下降.     

亚热带溪流中树叶凋落物多酚含量对树叶分解过程的影响

利用邻二氮菲-铁(Ⅲ)分光光度法测定了蒲桃与人面子树叶在二级溪流中分解时植物多酚含量的变化,并研究了多酚含量对树叶分解速率、底栖动物定殖以及微生物呼吸量的影响。结果表明,蒲桃叶片中初始多酚含量(19 %)比人面子树叶的含量高(6 %),其分解速率(分解系数k=0.01 d-1)比人面子树叶慢(k=0.04 d-1 )。研究还发现,蒲桃叶片上的微生物呼吸量比人面子的低(每克叶片单位时间的耗氧量分别为0.2 和0.4毫克),而且底栖动物中撕食者的种类和数量也比人面子树叶少。说明蒲桃叶片中较高的多酚含量抑制了微生物的活性和底栖动物的取食,从而减缓了蒲桃树叶的分解进程,表明叶片中多酚含量与树叶凋落物分解速率呈负相关关系。     

两种树叶在华南地区陆地与水环境中的分解速率比较

利用粗细2种孔径的分解袋对两种树叶（蒲桃和白兰）在广州长岗山自然保护小区的陆地和池塘中分别进行了为期210d和60d的分解研究。在陆地环境中,蒲桃在粗细网袋中的分解速率分别为0．003318d^-1和0．003728d^-1,白兰在粗细网袋中的分解速率分别为0．009238d^-1和0．004379d^-1;在静水环境中,蒲桃在粗细网袋中的分解速率分别为0．009536d^-1和0．012591d^-1,白兰在粗细网袋中的分解速率分别为0．017949d^-1和0．020759d^-1。结果表明,两种树叶在陆地中的分解速率均慢于水环境。另外,由于富含丹宁的蒲桃叶片具有抑菌作用,因此,无论在陆地还是水环境,蒲桃树叶的分解速率均慢于白兰树叶。     

两种树叶在华南地区贫营养型池塘中的分解速率研究

在热带亚热带地区,凋落物在湖泊、湿地中的分解过程知之甚少。为了解亚热带地区树叶凋落物在静水环境中的分解状况,利用分解网袋法对2种树叶（大叶相思和人心果）在广州长岗山自然保护小区一贫营养型池塘中进行了为期130d的树叶分解研究。结果显示,两种树叶在池塘中的分解速度非常缓慢,130d后大叶相思和人心果树叶的干重剩余率分别为74.3％和77．5％,经指数衰减模型拟合,两者的分解速率系数（k）分别为0．00145d^-1和0．00105d^-1。定殖在两种树叶上的大型底栖动物仅5种,其中优势类群为摇蚊幼虫和钩虾。结果表明寡营养型池塘中大型底栖动物功能摄食群中撕食者种类与数量的稀少是引起这两种树叶分解缓慢的主要因素之一。     

蒲桃和人面子叶片单宁含量与凋落物分解速率及底栖动物定殖的关系

在广州龙洞水库一条天然2级溪流中,测定了蒲桃和人面子凋落物105 d分解过程中单宁含量的变化.结果表明：蒲桃叶片单宁的初始含量（0.191 g·g^-1DM）高于人面子（0.057 g·g^-1DM）.在最初一周内, 两种树木叶片的单宁含量分别下降了45 %和22 %,其中人面子叶片单宁含量降速比蒲桃快;21 d后,其下降速度减缓,而凋落物分解的速度加快,人面子叶片分解比蒲桃迅速（k值分别为0.038和0.013 d^-1）.定殖在人面子叶片上的底栖动物的平均密度显著高于蒲桃叶片（P<0.05）,分别为每克叶片287.9头和26.2头;底栖动物的数量变化随叶片单宁含量的降低而呈逐渐增加趋势.富含单宁成分的蒲桃叶片分解速率缓慢,可能是凋落物中高浓度缩合单宁抑制了底栖动物,尤其是撕食者的定殖所致.     

大型底栖无脊椎动物对溪流中三角枫落叶分解的影响

采用复合网袋法,研究了冬季南京紫金山三角枫落叶在无干扰溪流和生态恢复溪流中的分解过程.结果表明：112 d后,三角枫落叶无灰干质量剩余率为31％～62％,分解速率符合指数衰减模型(P<0.05).在生态恢复溪流和无干扰溪流的流水生境中, 三角枫落叶的分解速率分别为0.0030 d^-1和0.0064 d^-1,静水生境中分别为0.0018 d^-1和0.0016 d^-1.流水生境中,无干扰溪流网袋内的大型底栖动物多度和生物量显著高于恢复溪流(P<0.05),而静水中无显著差异(P>0.05).无干扰溪流中的撕食者多度比例最高(70.4%),以栉水虱为主;生态恢复溪流中滤食者的多度比例最高(37.8%),以长跗摇蚊属为主.流水生境中三角枫落叶的分解速率与撕食者物种丰富度和多度相关性显著(P<0.01),而与生物量的相关性不显著(P>0.05).说明冬季溪流中撕食者的物种丰富度和多度决定三角枫落叶的分解速率.     

广东横石水河流域溪流大型底栖动物漂流的昼夜节律

比较了广东横石水河流域二条相邻的3级溪流大型底栖动物的漂流种类组成及昼夜节律，其中一条溪流受广东大宝山矿外排的酸性矿山废水严重污染，水体pH值仅为3.45且重金属严重超标，而另一条为相邻的清洁溪流.结果表明：清洁溪流中大型底栖动物的数量和种类远比受酸性矿山废水污染的溪流丰富.在清洁溪流中共采获漂流底栖动物6 871头，隶属10目52类群，其中水生昆虫的数量和种类占绝对优势 (99.5%).但总漂流密度占优势的类群（相对多度超过5%）不多，主要集中在以下几种水生昆虫：七鳃假二翅蜉 (28.5%)、宜兴似动蜉 (13.8%)、短脉纹石蛾(13.2%)、白背锯形蜉（7.5%)、摇蚊科(6.5%) 和肖扁泥甲(5.0%).蜉蝣目种类和数量最多，占全部漂流底栖动物总个体数的65%，其中又以四节蜉科居多，占蜉蝣目总个体数的63%.毛翅目昆虫的数量（18%）仅次于蜉蝣目.大型底栖动物的漂流表现出明显的昼夜节律，漂流主要在夜间进行，未发现有日漂者.漂流密度高峰出现在21:00和2:00，漂流密度分别为（70.3±10.8）和（289.0±124.6） 头·100 m^-3.大多数优势种类漂流高峰出现的时段略有不同，但有些优势种类（如摇蚊科和肖扁泥甲）并未表现出明显的漂流昼夜差异.在受酸性矿山废水污染的溪流中，漂流动物只有1种嗜酸性的多足摇蚊，其漂流活动也在夜间进行，并有3个明显的漂流高峰，分别出现在19:00、0:00和4:00，最高漂流密度仅为（6.7±5.2)头·100m^-3.说明酸性矿山废水不仅降低了溪流中漂流底栖动物的物种多样性和数量，也改变了其漂流模式.     

硫铁矿酸性矿山废水对大型底栖动物群落结构的影响

2006年11月和2007年1月通过金属和生物指标的量化监测，就酸性矿山废水对大型底栖动物群落结构的影响及高岚河污染现状进行研究。典型对应分析表明：酸性废水对高岚河上游大型底栖动物群落结构影响最大。对高岚河大型底栖动物群落结构和功能摄食类群进行分析，研究硫铁矿酸性矿山废水对河流大型底栖动物群落的影响，结果表明：高岚河自矿源起约16km河段，大型底栖动物群落结构已经遭到严重破坏；多足摇蚊Polypedilum tritum和真凯氏摇蚊Eukiefferiellab rehmi对酸和金属均具有较强的耐受力；捕食者和刮食者对矿山酸性废水带来的污染反应最为敏感。逐步回归分析表明：大型底栖动物生物多样性受Al、Ca、Cd、Fe、Mg、Mn等金属影响最大；密度受Ca、Cr和Mg的影响最大。     

树叶凋落物的分解速率对酸性矿山废水污染的响应

按照广东大宝山矿酸性矿山废水对横石水河的酸性污染梯度,从上游到下游在横石水河及其支流设置7个污染样点、3个清洁样点,利用孔径为0.5 mm的分解网袋采集了2种树叶(藜蒴,Castanopsis fissa;荷木,Schima superba),研究树叶凋落物在不同污染梯度下的分解状况.结果表明,随着pH值逐渐升高,水体重金属浓度逐渐降低,2种树叶的分解速率逐渐加快,各污染样点的分解速率均显著低于清洁样点的分解速率(P<0.05),其中藜蒴和荷木的树叶凋落物在清洁点I点的分解速率分别比距离污染源头最近、污染最重的样点A快6.5和10.5倍.回归分析表明,2种树叶的分解速率均与河流的pH值呈正相关.与河流的Cu、Cd、Zn、Pb 4种重金属浓度呈负相关,即河流pH值越低,重金属含量越高,树叶分解速率越慢.说明树叶凋落物的分解速率对水质变化是比较敏感的,可以作为评价河流生态系统完整性的一个参数.     

酸性矿山废水对底栖藻类的影响

酸性矿山废水中低的pH和高浓度的重金属对水生态系统影响巨大.依据"参照(Control)-受损(Impaired)-恢复(Recovery)"的设计方法,对高岚河受酸性矿山废水影响的河段、不受影响的河段及恢复河段进行对比分析.结果表明底栖藻类密度、叶绿素a浓度、无灰干重及自养指数等受酸性矿山废水影响明显,且枯水期酸性矿山废水的影响更显著.相关分析表明自养指数与各金属显著正相关而与pH值显著负相关,可以很好地指示矿山酸性废水对底栖藻类的影响.     

Effect of sudden flow reduction on the decomposition of alder leaves (Alnus glutinosa [L.] Gaertn.) in a temperate lowland stream: a mesocosm study

Climate change leads to summer low flow conditions and premature litter input in lowland streams in Central Europe. This may cause a sudden reduction of flow and fragmentation into isolated pools of permanently flowing streams, with a simultaneous increase in the food supply for detrivores during summer months. We performed a mesocosm study to investigate shredder and microbial mediated litter decomposition under these conditions. Leaf litter was placed in a lowland stream with a natural flow regime (reference) and in a stream mesocosm with significant flow reduction (FR) and a representative density of macroinvertebrates and detritus. Physicochemical parameters, leaf mass loss, macroinvertebrate abundance and biomass, leaf-associated respiration, fungal sporulation, and biomass were measured at regular intervals for 6 weeks. Coarse and fine-mesh bags were used to include or exclude macroinvertebrate shredders. In the coarse-mesh bags, leaf mass loss was significantly lower in the FR system than in the reference regime. In the fine-mesh bags, leaf respiration, fungal sporulation, and biomass but not leaf mass losses were substantially lower with flow reduction. Chironomid larvae (Micropsectra spp.) appeared to effectively fragment leaf litter in fine-mesh bags. In the FR system, leaf respiration was higher in the coarse-than in the fine-mesh bags. Our results suggest that, in temperate lowland streams, premature litter input during or after a sudden fragmentation into isolated pools and a reduction of stream flow reduces direct shredder-mediated litter decomposition, but shredders may indirectly influence the decomposition process. Handling editor: B. Oertli     

The influence of different litter bag designs on the breakdown of leaf material in a small mountain stream

Leaf breakdown of two riparian tree species, Cunonia capensis L. and Ilex mitis (L.) Radlk. was investigated in vitro at Window Stream, Table Mountain, using three different designs of litter bag. Breakdown of Cunonia and Ilex in coarse-mesh (5 mm) litter bags was very rapid (respectively 14.79 and 13.93% loss d^–1), and was significantly greater than the loss of leaf material of 1% d^–1 for both species from fine-mesh bags (180 µm). Differences recorded between fine-mesh and composite-mesh bags (180 µm mesh with 5 mm mesh top) represented macro-invertebrate ingestion, and at t = 28 d, amounted to 67.57% material loss in Cunonia and 62.58% in Ilex. The losses due to microbial activity and leaching, 31.28% in Cunonia and 29.17% in Ilex were not significantly different. Weight loss of Cunonia in coarse-mesh bags (14.79% loss d^–1) and in composite-mesh bags (13.93% loss d^–1) did not differ, but this was not the case for Ilex, where a significantly higher rate of loss in coarse-mesh bags (13.93% loss d^–1) than in composite-mesh bags (7.69% loss d^–1) was observed. This difference was used to quantify fragmentation losses. It was concluded that future leaf breakdown experiments in mountain streams must take cognisance of differential fragmentation losses before inferences can be made as to both invertebrate feeding preferences and biological decomposition of leaves.     

Role of transported particulate organic matter in the macroinvertebrate colonization of litter bags in streams

1. The exposure of mesh litter bags has been widely used to investigate the role of benthic macroinvertebrates in leaf processing in freshwaters. In this sense, several studies have related litter bag breakdown rates to the presence of colonizing invertebrates. A possible confounding factor in such experiments is that the litter bags trap suspended particulate organic matter that can itself attract invertebrate colonists, irrespective of the intended experimental treatment.
2. We attempted to quantify the accumulation of particulate organic matter (POM) within litter bags and to investigate its possible impact on macroinvertebrate density and richness. In seven headwater forested streams we exposed mesh bags filled either with beech leaves ( Fagus sylvatica ) or with plastic strips of an equal surface area.
3. Principal component analysis (PCA) showed that bag type and stream were the main explanatory variables for invertebrate colonization and POM accumulation within the bags. In contrast, there was little variation among sampling dates (6.4% of the total inertia).
4. The accumulated POM within the bags was substantial (up to 8.83 g ash-free dry mass (AFDM)) but highly variable among sites (mean from 0.32 to 4.58 g AFDM). At each of the seven sites, both richness and abundance of invertebrates were positively correlated with the mass of accumulated POM in bags. Macroinvertebrate colonization (notably taxon richness) was directly linked with the quantity of POM accumulated.
5. Our findings provide evidence of a potential pitfall in linking invertebrates to litter processing in mesh bags, particularly when large amounts of POM, entrained in stream flow, accumulate within the bags. An evaluation of the POM mass trapped in litter bags could account for the erratic patterns sometimes observed in their colonization by invertebrates.     

Effects of shredding amphipod density on watercress Nasturtium officinale breakdown

Shredding stream invertebrates should have a positive influence on the breakdown rates of leaf litter via direct consumption and particle fragmentation. To determine the effects of shredder density on litter breakdown, breakdown of the emergent stream macrophyte, Nasturtium officinale , was investigated using three litter bag mesh sizes [fine (0.2 mm), medium (1 mm) and coarse (3 mm) mesh] and four stocking densities of the shredder, Gammarus pseudolimnaeus , (0, 4, 8 and 16 per bag). Watercress decayed very rapidly, with breakdown rates ( k values) ranging from 0.075 d^-1 for fine mesh with no shredders to 0.24 d^-1 for coarse mesh. Stocked Gammarus increased breakdown rates significantly in fine mesh bags (p < 0.001), but only marginally in medium mesh bags (p < 0.1). Breakdown rates also increased significantly with mesh size. A regression model showed a significant relation of breakdown rate to Gammarus density and mesh size. These results clearly show that shredders can significantly influence breakdown rates and can account for up to 30% of breakdown, but that mesh size effects such as particle size reduction and loss are also very important.     

Leaf‐Litter Mixtures Affect Breakdown and Macroinvertebrate Colonization Rates in a Stream Ecosystem

Previous work in terrestrial and aquatic ecosystems has suggested that the relationship between breakdown rates of leaf litter and plant species richness may change unpredictability due to non‐additive effects mediated by the presence of key‐species. By using single‐ and mixed‐species leaf bags (7 possible combinations of three litter species differing in toughness; common alder [Alnus glutinosa ], sweet chestnut [Castanea sativa ], and Spanish oak [Quercus ilex ilex ]), I tested whether leaf species diversity, measured as richness and composition, affects breakdown dynamics and macroinvertebrate colonization (abundance, richness and composition) during 90 days incubation in a stream. Decomposition rates were additive, i.e., observed decomposition rates were not different from expected ones. However, decomposition rates of individual leaf species were affected by the mixture, i.e., there were species‐specific responses to mixing litter. The invertebrate communities colonizing the mixtures were not richer and more diverse in mixtures than in single‐species leaf bags. On the opposite, mixing leaf species had a negative, non‐additive effect on rates of shredder and taxa colonization and on macroinvertebrate diversity. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effect of Macroinvertebrate Exclusion on Leaf Breakdown Rates in a Tropical Headwater Stream1

The role of macroinvertebrates in the process of leaf breakdown is well studied in temperate streams, but less is known about their role in the tropics. We investigated the effect of reducing macroinvertebrate access to leaf material on leaf breakdown rates in a forested headwater stream in the Luquillo Experimental Forest, Puerto Rico. We measured leaf mass loss using fine and coarse mesh bags over 12 weeks for two common riparian species: Cecropia schreberiana (Moraceae) and Dacryodes excelsa (Burseraceae). Coarse mesh allowed freshwater shrimp and other macroinvertebrates to access leaf material, while fine mesh did not. Leaf breakdown rates did not differ between C. schreberiana and D. excelsa in coarse mesh bags (?0.0375/day vs. ?0.0395/day, respectively), but C. schreberiana breakdown was significantly slower than D. excelsa in fine mesh bags (?0.0159/day vs. ?0.0266/day). Additionally, breakdown in fine mesh bags was significantly slower compared to coarse mesh bags for C. schreberiana, but less so for D. excelsa. Breakdown rates for all treatments were fast relative to those in temperate‐zone streams indicating that both macroinvertebrates and macroinvertebrate‐independent processing can strongly influence leaf decomposition in tropical streams. The difference between C. schreberiana and D. excelsa indicates that the effect of macroinvertebrate exclusion can change with leaf type.