Effect of legume understorey on decomposition and nutrient content of eucalypt forest litter

Summary In Jarrah (Eucalyptus marginata Donn ex Sm.) forest of south-western Australia dense germination and regeneration of the native legumeAcacia Pulchella R. Br. can occur following moderate to high intensity fire. The effect of this legume understorey on rate of decomposition and change in nutrient content ofE. marginata litter was investigated using the mesh bag techniques and by examining four components of forest floor litter representing increasing stages of decomposition. E. marginata leaf litter confined in mesh bags lost 37% of its initial dry weight in the first 8 months on the forest floor and 44% of its initial dry weight after 20 months. During this period weight loss was similar for leaf litter located in forest without legume understorey and for leaf litter placed under dense stands ofA. pulchella. MixingA. pulchella litter withE. marginata litter had no significant effect on rate ofE. marginata litter breakdown. The presence of understorey vegetation had a marked effect on chemical composition of decomposingE. marginata leaves. After 8 and 20 months exposure on the forest floor, leaf litter in mesh bags placed underA. pulchella understorey had significantly (P<0.001) higher concentration and contained significantly (P<0.001) greater amounts of N, P, K, S, Ca and Mg than leaf litter placed in areas without legume understorey. This effect was particularly marked for N and P. In forest without legume understorey the amounts of these two nutrients inE. marginata leaf litter changed little during the first 20 months of decomposition, but forE. marginata leaf litter in mesh bags underA. pulchella there were absolute gains of up to 68% in the amount of N and 109% in the amount of P during this period. This represents accumulation of N and P from sources outside the litter bags. The concentration of N, P, S, Ca and Mg were higher at each of the four stages of decomposition in eucalypt leaf litter collected from the forest floor beneathA. pulchella compared to eucalypt leaf litter collected in forest without understorey. Concentrations of N, P and S increased with stage of decomposition. Levels of these three nutrients in eucalypt litter from under the legume were 1.5 to 2.9 fold higher than in the same component of litter from forest without understorey. The effect of legume understorey on nutrient concentrations in the forest floor and on Cielement ratios in decomposing litter is discussed in relation to long term rates of litter breakdown and net mineralisation of litter nutrients.     

The influence of invertebrates on the breakdown ofPotamogeton pectinatus L. in a coastal marina (Zandvlei,South Africa)

The influence of invertebrates upon the decomposition ofPotamogeton pectinatus L. in a coastal Marina system was examined over 112 days using litter bags. Invertebrate inclusion bags (2 mm mesh, 5 mm holes) registered a dry mass loss of 1% d^–1, while exclusion litter bags (80 µm mesh) produced a 0.4% mass loss d^–1 (a 2.5 fold difference). Losses of ash and N from inclusion bags were greater than those from exclusion bags (p < 0.05). There was a three fold difference between the two treatments in the time taken for litter to breakdown to half the initial stock: T_1/2 for inclusion bags = 43 d, exclusion bags = 130 d. In both treatments, minerals showed an expected rapid loss, due to leaching, with a subsequent slow increase relative to the dry material remaining. A total of nine invertebrate taxa was recorded from inclusion bags, with a peak biomass of 64 mg g^–1 dry massPotamogeton bag^–1 reached at 64 days after immersion. Grazing amphipods,Melita zeylanica Stebbing andAustrochiltonia subtenuis (Barnard), numerically dominated the litter bag fauna, whileM. zeylanica and nymphs of the zygopteran predatorIschnura senegalensis (Rambur) formed most of the biomass. Scanning Electron Microscopy indicated heavy grazing of micro-organisms by invertebrates, with major qualitative differences occurring 112 days after immersion. Invertebrates significantly accelerated the rate of litter breakdown through their feeding activities, assisting fragmentation and thus contributing to plant losses and also by increasing the surface area for microbial colonisation and attack.     

Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter

Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C₄), Sorghastrum nutans (C₄), and Poa pratensis (C₃) plants that were grown in large open-top chambers under ambient or twice ambient CO₂ and with or without nitrogen fertilization (45 kg N ha⁻¹). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO₂ on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However, there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C₄ grasses. We conclude that an indirect effect of CO₂ on decomposition and nutrient cycling could occur if CO₂ induces changes in the relative aboveground biomass of the prairie species.     

Variation in the decomposition of Phragmites australis litter in a monomictic lake: the role of gammarids

A decomposition study has been carried out in Lake Geestmerambacht, a moderately deep (max. ca. 22 m), monomictic slightly brackish lake in The Netherlands. To assess the relative importance of biotic (benthos) and physico-chemical factors, the mass loss rate (K) of reed leaf litter was measured at 10 sites, both in winter and in summer, in the absence (`protected' litter bags) and the presence (`unprotected' litter bags) of invertebrates. The aim was to investigate the variation in mass loss rate within the habitat and between seasons, and the role of the litter-associated invertebrate community. The experiments showed high spatial variation in decomposition rates. The spatial pattern changed with season. In summer, decomposition rates were higher than in winter: 4.4 times in the presence of invertebrates, and 2.6 times in their absence. The exclusion of invertebrates (`protected' litter bags versus `unprotected' litter bags) led to significantly lower decomposition rates. In particular, the decomposition rate was strongly correlated with the number of gammarids, the dominant taxon in the litter bags, which are well known for their ability to feed on leaf litter. The abundance of gammarids was directly correlated to the level of dissolved oxygen and inversely correlated to the effective fetch in summer, when the spatial structure of the decomposition process was evident. Therefore, the results of this study indicate that there are seasonal and spatial differences in the rate of detritus decomposition, most likely due to changes in habitat characteristics that influence the distribution of gammarids, key-species responsible for the first steps of the leaf breakdown in Lake Geestmerambacht. The spatial dependency of the process leads to formation of heterogeneous ecological patches in which the probability of disturbance propagation may vary.     

干旱与半干旱区灌丛微生境中红砂枯落物分解特征及中小型节肢动物的作用

在干旱区(内蒙古乌拉特后旗)和半干旱区(宁夏盐池)荒漠草原区,选择柠条灌丛内外微生境为研究样地,以红砂枯落物为研究对象,利用2种规格网孔分解袋(30目和250目网孔),探索中小型节肢动物在红砂枯落物分解过程中的作用规律,研究灌丛微生境中红砂枯落物质量损失变化特征及节肢动物群落的贡献。结果表明：(1)在干旱与半干旱区,红砂枯落物分解常数K均表现为灌丛内外微生境间无显著差异,且有无节肢动物参与对K的影响均较小。(2)分解至12个月时,无节肢动物参与的情况下,干旱与半干旱区红砂枯落物残留率均表现为裸地显著低于灌丛;但有节肢动物参与时,枯落物残留率则表现为灌丛内外微生境间无显著差异。分解至44个月时,无节肢动物参与的情况下,仅在干旱区枯落物残留率表现为裸地显著高于灌丛;而有节肢动物参与时,干旱与半干旱区枯落物残留率均表现为灌丛内外微生境间无显著差异。(3)节肢动物对红砂枯落物质量损失的贡献率呈现单峰值现象,且在分解至24个月时达到峰值。枯落物分解至12个月时,仅半干旱区节肢动物对红砂枯落物分解的贡献率表现为裸地显著低于灌丛;分解至44个月时,仅干旱区节肢动物对红砂枯落物分解的贡献率表现为裸地显...     

The failure of nitrogen and lignin control of decomposition in a North American desert

We measured mass losses of both buried and surface litter of six litter types: leaves of the perennial evergreen shrub, Larrea tridentata, leaves of the winter deciduous perennials Fluorensia cernua, Prosopis glandulosa and Chilopsis linearis (a desert riparian species), an evergreen monocot, Yucca elata, and a mixture of annual plants. These species differed in lignin content and carbon-nitrogen ratios. There was no correlation between rates of mass loss and percent lignin, carbon-nitrogen ratio, or lignin-nitrogen ratio. The leaves of F. cernua and the mixed annuals exhibited the highest rates of mass loss. Surface litter of Y. elata, the mixed annuals and C. linearis exhibited higher mass loss than buried litter of the same species. The patterns of mass loss of buried and surface litter differed with buried litter mass loss occurring as a negative exponential and surface litter exhibiting low rates in winter and spring and high rates in summer. There was no correlation between mass loss in surface bags that were field exposed for 1 month and actual evapotranspiration (AET) but there was a correlation between AET and mass losses in buried litter. A model relating mass loss to AET and initial lignin content underestimated mass losses in all species examined.     

Holcus lanatus invasion slows decomposition through its interaction with a macroinvertebrate detritivore, Porcellio scaber

Detritus based food webs may mediate the impacts of invasive species on ecosystem processes. Holcus lanatus (L.) is an invasive perennial grass that is rapidly spreading in the coastal prairie of California. We used litterbags to determine if H. lanatus altered the rate of litter decomposition through its interaction with the dominant macroinvertebrate detritivore at our study site, the isopod Porcellio scaber (Latreille). Over the course of a year, H. lanatus litter loss was 15% less than annual grasses, a difference that was directly attributable to P. scaber. Although there was no effect of isopods on litter loss during the winter, when most decomposition occurred, isopods had substantial effects on litter loss of annual grasses during the summer. P. scaber had no effect on litter loss of H. lanatus litter. Our findings suggest that H. lanatus invasion slows decomposition in the coastal prairie because it is unusually refractory to an important detritivore. The decreased decomposition of H. lanatus litter, along with increased production during the growing season, lead to a doubling of the end-of-season litter biomass where H. lanatus had invaded.     

In situ studies on the breakdown ofNymphoides peltata (Gmel.) O. Kuntze (Menyanthaceae); Some methodological aspects of the litter bag technique

Summary Thein situ breakdown ofNymphoides peltata (Gmel.) O. Kuntze has been studied with special attention for methodology by: (1) using fresh and pre-dried material to establish the influence of pre-drying on breakdown and losses of nutrient stocks during decomposition; (2) enclosing different amounts of material in litter bags; (3) using litter bags with different mesh sizes, and (4) placing litter bags in water (floating leaves, petioles), on the sediment (long shoots) and in the hydrosoil (short shoots, roots). Of the material incubated in water, the floating leaves decomposed at a faster rate than the petioles, while the long shoots had the slowest breakdown. In the sediment the short shoots disappeared at a faster rate than the roots. By incubating the same morphological structure, both in the water and the sediment it appeared that the rate of breakdown was faster in the upper layers of the sediment. Pre-dried plant parts showed in water a larger initial weight loss than normal senescent plant parts, while in the sediment dried plant parts had a significantly slower loss of mass than the freshly incubated structures. Losses of nutrient stocks during decomposition were also markedly altered by pre-drying the material. When a larger amount ofNymphoides material was enclosed in the bags a tendency of a faster decay could be demonstrated. Macro-invertebrates colonized the litter bags with the 0.5 mm mesh size but usually could not-enter the 0.25 mm mesh size bags. The browsing of the detritivores did not result in a faster disappearance of organic matter, but organic matter must have been transported into the bags resulting in a larger amount of remaining organic matter when compared with the 0.25 mm mesh size bags.     

Evaluation of the faster initial decomposition of tropical floating leaves ofNymphaea elegans Hook

Contributions of abiotic and biotic processes to the decomposition of floating leaves ofNymphaea elegans were separately evaluated by comparing the rate obtained from anin situ experiment of submerging dry leaf material in a lake, and that from a laboratory experiment of submerging dry leaf material in lake water with a bio-fixing reagent. It took 8 days to decompose 79.4% of the initial dry weight of the floating leaf ofN. elegans in a tropical lake. Of the dry weight loss, 32.9% and 67.1% were atributed to abiotic and biotic decomposition, respectively. The relationship between decomposition rate and the mesh size of the leaf litter bags was examined by the application of a mathematical model. A reasonable value of decomposition loss at an early stage could be obtained using a bag with a mesh opening of 9.9 mm². The decomposition rate of floating leaves is faster than that of other aquatic plants. Rapid decomposition ofN. elegans leaves may be attributed to the fact that the plant has a low carbon to nitrogen ratio.     

Decomposition of emergent macrophytes in a Wisconsin marsh

Loss of both dry weight and nutrients during decomposition was measured using litter bags, both in a natural marsh and in controlled experiments. At 348 days dry weight remains of Typha latifolia, Sparganium eurycarpum, Scirpus fluviatilis shoot litter in the marsh were 47.5, 26.9, 51.4% respectively, and for the rootrhizome litter were 59.1, 42.1, 27.8% (Scirpus > Sparganium > Typha). Under controlled conditions both temperature and type of water produced significant effect on dry weight loss of Typha leaves. Sterilization and antibiotics effectively inhibited the growth and activities of decomposers. Initial weight, N, P, Ca, and Mg losses resulted chiefly from leaching. These elements accumulated in spring and summer; N exhibited the highest accumulation. In the laboratory, N accumulation occurred within 15 days, as a result of microorganisms inhabiting the litter. Increase in P, Ca, Mg in later stages of decomposition were attributed to microorganisms, epiphytes, and precipitation from solution. High C : N ratios and relatively low P, Ca, Mg in original standing crop may be the cause of low herbivore consumption, whereas the relative increases in N, P, Ca, Mg in decomposed litter provide a more nutrient-rich substrate for detritivores. Much of the nutrient uptake in the annual cycle is via microbial and detritivore growth rather than by macrophyte producers.     

Leaf decomposition in an experimentally acidified stream channel

Decomposition of Alnus rugosa and Myrica Gale leaves immersed in artificial stream channels fed by a small headwater creek was followed over a three month period. At the end of experiment, remaining weights of both leaf types confined in litter bags were significantly higher after immersion in experimentally acidified water (pH 4.0) than when immersed in control water (pH 6.2–7.0). For both types of leaves and for all sampling times, there was generally no difference in the C:N ratios between leaves in acidified and those in control water. In control water, oxygen uptake by microorganism on A. rugosa leaves was significantly higher after 46 days of immersion, whereas differences between treatments appeared only after 69 days for M. Gale leaves. Transfer of A. rugosa leaves from acid to control water led to a rapid increase in microbial activity; this increased activity was reflected in a fast weight loss of the leaves. For both leaf types, total numbers of macroinvertebrates were usually higher in litter bags immersed in control water. Macroinvertebrates colonizing the litter bags were mainly collector-gatherers: Chironomidae were numerically dominant in control leaf packs whereas Oligochaeta dominated in acid leaf packs. Macroinvertebrate biomass in M. Gale litter was higher in control than in acidified water, which contrasted with macroinvertebrate biomass in A. rugosa leaf packs which was not significantly different between treatments. Macroinvertebrate contribution to the breakdown of leaf litter was thus considered less important than the microbial contribution. This study demonstrated that decomposition of leaf litter in acidic headwater streams can be seriously reduced, mainly as a result of a lower microbial activity.     

西双版纳热带季节雨林凋落叶分解与土壤动物群落：两种网孔分解袋的分解实验比较

 以西双版纳热带湿性季节沟谷雨林混合凋落叶作为分解基质,在不同位置季节雨林样地,采用不同网孔（ 2和0.15 mm）分解袋,开展大中型土壤动物对雨林凋落叶分解影响的实验,测定了不同网孔分解袋土壤动 物多样性、凋落叶分解速率和主要养分元素释放状况。结果显示：2 mm网孔分解袋土壤动物类群相对密度 年均值为2.67～2.83目•g－1凋落物干重,个体相对密度年均值为22.3～21.77个•g－1凋落物干重,显著 高于0.15 mm网孔分解袋的类群相对密度0.27～0.28目•g－1凋落物干重和个体相对密度2.88～2.77个•g－ 1凋落物干重（p<0.01）,并且0.15 mm网孔分解袋中极少量的动物个体主要为小型类群弹尾目和蜱螨目（ 原生动物、湿生土壤动物线虫不计）,由此我们视2 mm网孔分解袋凋落叶分解由绝大多数土壤动物和其它 土壤生物共同作用,而0.15 mm网孔分解袋基本排除了大中型土壤动物对袋内凋落叶分解的影响。2 mm网 孔分解袋凋落叶物质失重率（71%左右）、分解率指数（1.88～2.44）和主要养分元素释放率明显高于 0.15 mm分解袋（34%～35%,0.48～0.58）。通过比较两种不同网孔分解袋凋落叶失重率和元素释放率的 差异,显示出季节雨林大中型土壤动物群落对凋落叶物质损失的贡献率为年均值46%左右,并使凋落叶C/N 和C/P明显降低,而对不同元素释放率的影响不同,其中对N、S和Ca元素释放率的影响较大,而对K素释放 的影响作用最小。相关分析显示,2 mm网孔分解袋内土壤动物群落类群和个体的相对密度与凋落叶物质残 留率有较好的负相关关系,而群落香农多样性指数与凋落叶分解率指数表现出一定的正相关关系。     

A modified litter bag design for use in lentic habitats

A modified litter bag design and handling procedure were tested to establish whether these reduced the exaggerated fragmentation losses that occur with standard litter bags. The modified design was compared with standard coarse (5 mm) and fine (0.25 mm) mesh litter bags using Phragmitesleaf litter. All were positioned in a section of a reedbed subject to water level management but negligible water flow. Breakdown rates were significantly reduced with the modified design but these were still significantly greater than those in the fine mesh bags. Owing to the extended period, results were influenced by invertebrates colonising the fine mesh bags. The significance of bag design and invertebrate colonisation are discussed.     

高山林线交错带高山杜鹃的凋落物分解

凋落物分解是维持生态系统生产力、养分循环、土壤有机质形成的关键生态过程。高山林线交错带是陆地生态系统中对气候变化响应的敏感区域。季节变化和海拔梯度上的植被类型差异可能会影响该区域凋落物的分解,进而对高山生态系统的碳氮循环产生重要影响。采用凋落物分解袋的方法,研究了川西高山林线交错带优势种高山杜鹃(Rhododendron lapponicum)凋落叶在雪被期和生长季的分解特征。结果显示:(1)季节变化和植被类型对高山杜鹃凋落物的分解均具有显著影响(P0.05),凋落叶的质量损失主要发生在生长季且在高山林线最大,暗针叶林中雪被期的质量损失略高于生长季,但差异不显著;(2)林线交错带上高山杜鹃凋落叶分解缓慢,一年干物质失重率为9.62%,拟合分解系数k为0.145;(3)高山杜鹃凋落叶的质量变化主要体现在纤维素降解显著且集中在雪被期,木质素无明显降解,在高山林线上C/N、C/P、木质素/N变化幅度较小且C、N、P的释放表现得稳定而持续。结果表明,季节性雪被对林线交错带内高山杜鹃分解的影响不仅局限在雪被期内,雪被融化期间频繁的冻融作用和雪融水淋洗作用可能会促进高山杜鹃凋落物在生长季初期的分解。总的来看,在气候变暖的情景下,雪被的缩减、生长季的延长和高山杜鹃群落的扩张可能加速高山林线交错带高山杜鹃凋落物的分解。     

Decomposition processes of Spartina maritima in a salt marsh of the Basque Country

Decomposition dynamics of aerial parts and root-rhizomes of Spartina maritima in a Basque Country salt marsh was studied, using litter bags placed on the soil surface and buried 10 cm below ground. Aerial parts of the plant in aboveground position showed higher breakdown rates than samples placed belowground. There was no significant difference found between aerial parts and root-rhizomes buried. Nitrogen and phosphorus followed different dynamics (seasonal changes and progressive losses) that may be a consequence of distinctive mineralization pathways. The low faunal richness and densities belowground reflect the unfavourable life conditions in such a situation and, to a certain extent, the lower decomposition rates of buried litter. Four mathematical expressions that fit the data are presented and discussed.     

Connecting plant–microbial interactions above and belowground: a fungal endophyte affects decomposition

Mutualisms can strongly affect the structure of communities, but their influence on ecosystem processes is not well resolved. Here we show that a plant–microbial mutualism affects the rate of leaf litter decomposition using the widespread interaction between tall fescue grass (Lolium arundinaceum) and the fungal endophyte Neotyphodium coenophialum. In grasses, fungal endophytes live symbiotically in the aboveground tissues, where the fungi gain protection and nutrients from their host and often protect host plants from biotic and abiotic stress. In a field experiment, decomposition rate depended on a complex interaction between the litter source (collected from endophyte-infected or endophyte-free plots), the decomposition microenvironment (endophyte-infected or endophyte-free plots), and the presence of mesoinvertebrates (manipulated by the mesh size of litter bags). Over all treatments, decomposition was slower for endophyte-infected fescue litter than for endophyte-free litter. When mesoinvertebrates were excluded using fine mesh and litter was placed in a microenvironment with the endophyte, the difference between endophyte-infected and endophyte-free litter was strongest. In the presence of mesoinvertebrates, endophyte-infected litter decomposed faster in microenvironments with the endophyte than in microenvironments lacking the endophyte, suggesting that plots differ in the detritivore assemblage. Indeed, the presence of the endophyte in plots shifted the composition of Collembola, with more Hypogastruridae in the presence of the endophyte and more Isotomidae in endophyte-free plots. In a separate outdoor pot experiment, we did not find strong effects of the litter source or the soil microbial/microinvertebrate community on decomposition, which may reflect differences between pot and field conditions or other differences in methodology. Our work is among the first to demonstrate an effect of plant–endophyte mutualisms on ecosystem processes under field conditions.     

Decomposition of cellulose,soil organic matter and plant litter in a temperate grassland soil

The formation of mor humus in an experimental grassland plot, which has been acidified by long-term fertiliser treatment, has been studied by comparing the rates of cellulose, soil organic matter and plant litter decay with those in an adjacent plot with near-neutral pH and mull humus. The decomposition of cellulose filter paper in litter bags of 5 mm, 1-mm and 45-μm mesh size buried at 3 to 4 cm depth the plots was followed by measuring the weight loss and changes in glucose content over a 6 month period. Soil pH was either 5.3 or 4.3. Decomposition of native soil organic matter and plant litter in soil from the same plots were followed using CO₂ evolution in laboratory microcosms. Cellulose weight loss at pH 5.3 was greatest from the 5-mm mesh bags and least from the 45-um mesh bags. At pH 4.3 there was little weight loss from bags and no significant differences in weight loss between bags with different sized mesh. There was, however, a reduction in the glucose content of the hydrolysed and derivatised filter paper with time. The decomposition rate of native soil organic matter in the low pH soil was increased to that observed in the less acid soil when the pH of the former was increased from 4.3 to 5.3. The increase in decomposition rate of added plant litter in the more acid soil as a result of CA(OH)₂ addition was only 60% of that observed in the soil with pH 5.3. These data support the hypothesis that the absence of soil animals and the restricted microbial decomposition in the acidic soil was responsible for mor humus formation.     

Advances in the positional cloning of nodulation genes in soybean

The effect of liming on the decomposition of Norway spruce needle litter was studied in 40–60-year-old Norway spruce stands. Finely-ground limestone had been spread about 30 years ago at a dose of 2 t ha^–1 and reliming was carried out about 20 yr later at a dose of 4 t ha^–1. Needle litter was collected from both control and limed plots, and it was placed in litter bags in the middle of the humus layer of the plot from which they originated, and similarly to the other plot in May. Litter bags were sampled after 4, 12 and 16 months. The site of origin of the needle litter, whether from control plot or from limed plot, affected mainly the early stages of decomposition. Initially the effect of liming was seen as decreased concentration of water soluble material and then, during decomposition, as decreased mass loss and decreased degradation of lignin, and increased C/N ratio. The incubation site, whether the control or the limed plot, did not affect decomposition significantly.Decomposition of Scots pine needles in a young Scots pine plantation was also studied. The treatments were: 2 t ha^–1 of finely-ground limestone and 2.5 t ha^–1 of bark ash spread 8 months before this study. The treatments did not affect decomposition much, but some stimulation of the treatments on decomposition was observed. Compared to spruce needles, the C/N ratio of pine seedles was lower, they contained less lignin and more water soluble material, and decomposed faster in the first summer.     

Decomposition of leaf litter of Dombeya goetzenii in the Njoro River, Kenya

Decomposition of the leaves of Dombeya goetzenii (K. Schum) in the Njoro River is described and analysed. The loss of the ash-free dry mass was rapid during the first 14 d of exposure in the wet and humid zones. The leaves in the litter bags in the humid and wet zones were processed at a rate (±SD) of 0.005±0.001 d^-1 and 0.021±0.001 d^-1, respectively. The processing rates of the leaves in the wet zone differed significantly from those observed in the humid zone (t-value, p<0.05). The interchanged litter bags (i.e. from wet to humid zones vice versa) showed that the processing rates of the leaves in the litter bags interchanged from the wet zone to the humid zone was about 200 times lower than that of the leaves retained in the wet zone throughout; fourfold higher in the leaves in the litter bags which were transferred to the wet zone than in those leaves of the litter bags which were retained in the humid zone throughout the experiment. It took approximately 38 months for 90% of the leaf dry mass to be processed in the humid zone whilst it took 4 months for a similar percentage to be processed in the wet zone. It is concluded that the immersion and emersion of leaf litter, which may occur in the wet and humid zones, respectively, are important aspects of the decomposition process which may influence the quantity of nutrients in stream ecosystems.     

Elephant dung decomposition and coprophilous fungi in two habitats of semi-arid Botswana

In order to understand the impact of habitat changes on ecosystem processes caused by increased populations of elephants, elephant dung decomposition was studied in semi-arid Botswana. Dung decomposition rates were studied with and without the presence of arthropods, using pairs of exposed dung and dung enclosed in nylon-mesh bags, respectively. Dung decomposition rates were lower in the absence of arthropods. The rates in the late wet season were higher in the scrubland than in the woodland. In the early dry season, immediately after the wet season, the rates were higher in the woodland than in the scrubland. The difference in decomposition rates between habitats was attributed to microclimatic conditions created by vegetation cover. With regard to fungal succession, Cladosporium cladosporioides and Eurotium brefeldianum occurred only in the late stages of dung decomposition whereas Talaromyces helicus, Cercophora coprophila and Sporormiella minima occurred in all the stages. Although there was no significant difference in Shannon–Weiner fungal species diversity index between habitats, seasons, dung ages and laboratory incubation periods, there were significant differences in fungal community composition between these parameters. Species richness was higher in the late wet season than in the early dry season, indicating the importance of moist conditions for a large diversity of fungal species.