Areas of endemism of the Patagonian steppe: an approach based on insect distributional patterns using endemicity analysis

Aims  To delimit areas of endemism in the Patagonian steppe using endemicity analysis (EA), which evaluates areas of endemism by means of an endemicity index, and to compare the resulting endemic areas with those proposed for the Patagonian steppe by previous authors.
Location  The Patagonian steppe, a region of South America found approximately below parallel 36° S to the east of the Andes Mountains.
Methods  Distributional data for 159 species of insects collected in the Patagonian steppe, and consisting of 1317 georeferenced samples were used to identify areas of endemism. A data grid of presence and absence (with cells of 1° × 1°) was constructed. Initially, two different types of EA were performed, seeking areas defined by 'four or more' species. A first analysis was performed without taking into consideration those quadrats where no species had been recorded (empty quadrats), which in many cases meant a discontinuous distribution. The second analysis was performed assuming a continuous distribution for each species. A third analysis, assuming continuous distributions, was performed using 'three or more' as the number of species necessary for an area to be identified as an endemic area.
Results  In the first two analyses, EA recognized the same five areas of endemism: western Patagonia, south-western Payunia, northern Suabandean, southern Subandean and Austral Patagonia. The results of the third analysis allowed the identification of three more areas of endemism: northern Payunia, Chubutian and Santacrucian.
Main conclusions  We identified five areas of endemism for the Patagonian steppe, some of which have been defined in previous contributions. These areas are: Western Patagonia, Payunia and Subandean Patagonia (which can be divided into septentrional and meridional), Central Patagonia (Chubutence and Santacrucense) and Austral Patagonia.     

Spatial and temporal patterns in the aquatic insect community of a high altitude Andean stream (Mendoza,Argentina)

Benthic invertebrate communities have been poorly studied in Andean streams apart from the Patagonian region. The primary objective of this work was to analyse the faunal composition at three different altitudes and to observe whether there were differences in aquatic insect community structure at spatial and temporal scales. Physicochemical variables were measured on a monthly basis. Sixteen families were found, the most frequent and abundant taxa being Massartellopsis (Ephemeroptera), Andesiops (Ephemeroptera), Metrichia neotropicalis (Trichoptera), Cailloma lucidula (Trichoptera), Austrelmis (Coleoptera), and the Chironomidae (Diptera). There was a change in benthic composition associated with land use and with the diminution of water quality from the headwaters to the mouth of the system. The middle reach was a transitional area where headwater species coexisted with species characteristic of the lower reach, with Austrelmis and the family Chironomidae being the most abundant elements.     

Effects of inorganic sedimentation and riparian clearing on benthic community metabolism in an agriculturally-disturbed stream

An in situ chamber technique was used to obtain seasonal estimates of benthic community metabolism at three stations in an agriculturally disturbed stream. Two stations with open canopies were examined. Sand was the dominant substrate at one site, cobble at the other. The third station was shaded by riparian vegetation and had a sand substrate.Seasonal estimates of net community productivity (NCP) and community respiration (CR) at the cobble section were significantly higher than those calculated for the sand sections (p>0.05). Ratios of gross community productivity (GCP) to 24 h respiration indicated autotrophic conditions in the cobble and extreme heterotrophy in the sand. NCP was significantly higher (p<0.05) in the open canopy sand than in the riparian shaded sand only when turbidity and discharge were low. Measurements of periphyton ash-free dry mass (AFDM) and chlorophyll a support metabolism estimates. Measurements of loose detrital AFDM were very low and variable compared to others reported in the literature. Therefore, allochthonously derived detritus may not be an important energy source for the benthic community.     

The impact of vertebrate and invertebrate predators on a stream benthic community

I assessed the impact of both vertebrate and invertebrate predators on a lotic benthic community in a 1-month-long experiment, using enclosures containing cobble/gravel bottoms, with large-mesh netting that allowed invertebrates to drift freely. Brown trout (Salmo trutta) and leeches (Erpobdella octoculata) were used as predators and four treatments were tested: a predator-free control, leeches only, trout only, and leeches and trout together. A density of 26.7 leeches/m² (20 leeches/enclosure) and 1.3 trout/m² (one trout per enclosure) was stocked into the enclosures. The total biomass of invertebrate prey was significantly lower in the trout and trout plus leech treatments than in the leech and control treatments, which were due to strong negative effects of trout on Gammarus. On the individual prey taxon level, both trout and leeches affected the abundance of Asellus , Baetis and Ephemerella, whereas the abundance of Gammarus was only affected by trout, and the abundance of Orthocladiinae and Limnephilidae was only affected by leeches. In the treatment with trout and leeches together, the abundance of Ephemerella and Baetis was higher than when trout or leeches were alone, which was probably due to predator interactions. Leeches and trout had no effects on prey immigration but did affect per capita emigration rates. Both trout and leeches indirectly increased periphyton biomass in enclosures, probably due to their strong effects on grazers. Both trout and leeches were size-selective predators, with trout selecting large prey, and leeches selecting small prey. Size-selective predation by trout and leeches affected the size structure of five commonly consumed prey taxa. Trout produced prey populations of small sizes owing to consumption of large prey as well as increased emigration out of enclosures by these large prey. Leech predation produced prey assemblages of larger size owing to consumption and increased emigration of small prey. These results suggest that in lotic habits, predatory invertebrates can be as strong interactors as vertebrate predators. Received: 23 June 1997 / Accepted: 4 May 1998     

Diet and trophic groups of an aquatic insect community in a tropical stream.

The diet and trophic groups of an assemblage of aquatic insects were studied in a tropical stream. Genera of the orders Ephemeroptera, Odonata, Plecoptera, Lepidoptera, and Hemiptera showed feeding specialization. Others, such as Trichoptera, Coleoptera, and Diptera, showed great diet variation with genera of different trophic groups. Seasonal variation of insect diet, evident only for some genera of the orders Trichoptera, Lepidoptera, Coleoptera, and Diptera, was due to the differences observed in community composition and to generalist habits of these genera. However, the seasonal comparison of trophic groups showed no significant statistical differences. The great importance of organic matter, a non-limited resource, in the diet of Ribeir?o do Atalho aquatic insects may be the explanation for the trophic stability in this community organization.     

First results on the water chemistry, algae and trophic status of an Andean acidic lake system of volcanic origin in Patagonia (Lake Caviahue)

The acidic caldera lake Caviahue (Patagonia, Argentina) and its main tributaries were studied on two dates during September 1998. The main results are: The acidity of the Lake Caviahue (pH: 2.56, acidity: >5 mmol H⁺ l^–1) is controlled by the extremely acidic Upper Rio Agrio (pH: 1.78, acidity: >20 mmol H⁺ l^–1). The high sulphate contents of both the river and the lake can be attributed to sulphuric acid generated by the uptake of sulphurous gases in the crater lake of Copahue Volcano at approximately 2800 m a.s.l. The high concentrations of both Fe and trace metals (e.g. Cr, Ni, Zn) in Lake Caviahue originate from sulphur–acid interactions with the predominantly volcanic geology of the catchment area. The P-rich andesitic geology influences both the Upper and Lower Rio Agrio and Lake Caviahue. Both were found to have high phosphorus concentrations (300–500 g P l^–1) indicative of a high potential for eutrophication. The plankton community consisted of bacterioplankton, phytoplankton and rotifers. The phytoplankton was dominated by one green alga, Keratococcus raphidioides (>90% of total abundance) followed by a green sphaerical and Chlamydomonas sp. The total phytoplankton density was about 15000 cells ml^–1 in the upper 10 m of the water column. Rotifers were represented by one bdelloid species and their abundance was highly variable (360–4040 ind l^–1) in the water columm. In the Upper and Lower Rio Agrio, the epilithic community was dominated by one chloroccocal species and two species of Ulothricales. According to trophic categories based on phytoplankton density and TP concentration, Lake Caviahue can be classified as mesotrophic/eutrophic. However, chlorophyll a concentrations observed were not in agreement with this state.     

Soil mediates the interaction of coexisting entomopathogenic nematodes with an insect host

We tested for soil substrate effects on the movement and infectivity of naturally co-occurring entomopathogenic nematodes Steinernema feltiae and Heterorhabditis marelatus, alone and in combination. We manipulated the presence and bulk density of soil and added Galleria mellonella baits within capped and perforated 15mL centrifuge tubes. Sampling tubes were then deployed in situ into field and laboratory settings as experimental traps for infective juveniles. In comparisons with standard soil collections from Lupinus arboreus rhizospheres, sampling tubes were equally sensitive to the presence of H. marelatus and more sensitive to S. feltiae. In laboratory microcosms, both EPN species infected Galleria at high frequencies in tubes lacking soil and in the absence of heterospecifics. Infection frequency of S. feltiae was unaffected by the presence of H. marelatus, but it declined with higher soil bulk density inside tubes. In contrast, detectable infection frequency by H. marelatus was reduced only marginally by the presence of soil but severely by the presence of S. feltiae. Thus, the presence of soil in tubes reversed the identity of dominant species infecting Galleria in tubes, an effect magnified when soils were compacted. Moreover, S. feltiae rarely moved into tubes lacking Galleria baits, whereas H. marelatus colonized unbaited tubes 4- to 5-fold more frequently than S. feltiae. In situ, sampling tubes acted as filters to reduce interference and contamination by fungal pathogens common in field soils. The method allows precision sampling with minimal soil disturbance while protecting bait insects from scavengers. Manipulation of tube design may allow selective sampling of EPN species, depending on the abiotic characteristics of soils, and the biology, behavior, and interspecific interactions of coexisting species.     

Effects of eutrophication on the interaction between algae and grazers in an Andean stream

Nutrient excess is a common disturbance that affects biological interactions in river ecosystems. The response of nutrient supply on primary producers and Tricorythodes sp., a common mayfly grazer, was determined in experimental chambers set in a tropical, high Andean stream. Chambers in an experimentally fertilized reach developed higher amount of both benthic and detached chlorophyll than chambers in an upstream control reach. Fertilization produced a slight increase in grazer biomass, and reduced algal biomass compared to grazer-free chambers. These results show that nutrient excess spread bottom-up effects through the food web, and that relevant top-down effects could also be detected. Eutrophication may produce relevant changes in the food web of tropical high-mountain streams.     

Ecohydrological effects of grazing‐induced degradation in the Patagonian Monte,Argentina

Water‐limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0–25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function.     

Seasonal predictability of benthic macroinvertebrate metrics and community structure with maturity-weighted abundances in a Missouri Ozark stream,USA

Benthic macroinvertebrates in lotic habitats are influenced by a wide range of physical and chemical environmental factors that change over a temporal continuum. Within a year, different species can occupy the same space at different points in time. Thus, the community structure itself is in flux from season to season. This study analyzed the structure of a riffle macroinvertebrate community in a single stream from a series of monthly samples over a year cycle. The goals of this study were to: (1) identify community measures that were least variable over the continuum and predict them in test samples from the next year; (2) explore the usefulness of maturity data in analyzing community structure; (3) construct a temporal River Invertebrate Prediction and Classification System like (RIVPACS-like) model that classifies seasons based on biota and predicts an expected community for any season. From a set of 120 metrics, nine metrics representing 5 measurement categories displaying low variability over the annual continuum were selected for multiple regression analysis. The Biotic Index was fairly predictable between years, regardless of season, whereas other measures were less so. Metrics with standard abundances compared to their maturity-weighted analogues revealed that measures based on finer taxonomic resolution or functional groups were more likely to differ. Three biologically determined seasons were identified from cluster analysis during the process of creating a multivariate predictive model. Temporal environmental variables were used to determine test date group membership and comparisons of expected to observed communities revealed that 1 of 3 test dates was predicted well by the model. Our results demonstrate that macroinvertebrate community structures can express high variability over a short period of time and this phenomenon deserves more understanding with regard to interpreting biological assessment results.     

Histochemical observations on the salmonids Salmo salar L. and Salmo trutta L. and the ephemeropterans Baetis rhodani (Pict.) and Ecdyonurus venosus (Fabr.) following a simulated episode of acidity in an upland stream

Salmonids (Salmo salar, Salmo trutta) and mayflies (Baetis rhodani, Ecdyonurus venosus) which had been exposed to simulated episodes of low pH, and low pH with elevated aluminium, were examined histochemically for the presence of aluminium and mucus. The control fish and mayflies and those exposed to low pH did not stain for aluminium, although increased mucus production was demonstrated in fish gills. Trout and salmon exposed to aluminium at low pH exhibited extensive aluminium and mucus coating of the secondary gill lamellae. No mucus was produced by mayflies but aluminium was apparent on all parts of the body. Mean aluminium concentrations of digested fish gills were 2950 and 3050 g g^–1 dry wt. for trout and salmon respectively, whilst for whole specimens of B. rhodani and E. venosus values were 1 200 and 3 175 g g^–1 dry wt.     

Emergence,maturation and upstream oviposition flights of Plecoptera from the Breitenbach,with notes on the adult phase as a possible control of stream insect populations

Upstream oviposition flights of several Plecoptera species of the genera Leuctra, Nemoura, Isoperla and Siphonoperla along the Breitenbach, Hesse, Germany are inferred from 1. oviposition occuring upstream from emergence areas; 2. size differences and size-shifts between emerging and egg-laying females; 3. concentration of oviposition in upstream sections of the emergence area. The last point relies on direct catches of egg-laying females with sticky traps, and on over-representation of old, mature females in upstream emergence traps towards the end of, or even after actual emergence periods. Criteria for age class discrimination of the respective taxa are described. The validity of the present and of other indirect evidence for directed adult flights and the significance of adult upstream displacement are discussed. Optical orientation cues are suggested. Females of Leuctra prima and Siphonoperla torrentium are shown to gain 25–50% dry weight by feeding in the terrestrial environment; general information indicates many other Plecoptera may be similar in this respect. Terrestrial adult life is shown to last for 3–8 weeks. This long time, evidence of important flight activity and feeding together suggest that the terrestrial phase is spent as an active adult, the inevitable risks of which may form an important control of population dynamics.     

Effects of land cover type on community structure and functional traits of alpine stream benthic macroinvertebrates

1. In the European Alps, due to the current changes in land use driven by different social and economic factors, grasslands and pastures are being increasingly replaced by forests. Whereas many studies have focused on the impacts of urbanisation and intensive agricultural activities, no study has evaluated the effects of changes among types of natural to semi-natural land cover in the Alps with a focus on lotic environments.
2. Here, combining taxonomic and functional approaches, we show the effects of four different alpine land cover types (rocks, grasslands, coniferous forests, valley bottom pastures) on stream benthic macroinvertebrate communities. Irrespective of elevation, grasslands and pastures exhibited unpredicted similarity in terms of the composition of the macroinvertebrate assemblages and hosted the highest diversity of benthic organisms, whereas in each of the other land cover types, the density and diversity of the faunal assemblages showed distinct and characteristic values.
3. When analysing the functional diversity decomposed to richness, evenness, and divergence components, grasslands and pastures again showed a similar trend, being characterised by high levels of resource exploitation and niche differentiation, with the potential to host additional organisms. However, as expected, differences driven by land cover type and elevation emerged when examining the single functional traits, since elevation played a major role in terms of the distribution of traits conferring resistance and resilience.
4. Our results demonstrate that land cover type is a prominent factor influencing the taxonomic and functional variety of stream benthic macroinvertebrate communities. Moreover, alpine grasslands contained an unexpected diversity of aquatic insects, as previously assessed for other organisms (e.g. plants and snails). Overall, our study highlights the importance of the preservation of the diversity of habitats in the alpine region, with a special focus needed for valuable semi-natural landscapes, such as grasslands and pastures, particularly in a time of increasing intensification and abandonment of lands in the alpine context.

     

Application of nanoparticles in cancer therapy with an emphasis on cell cycle

Owing to their unique characteristics, nanoparticles (NPs) could be incorporated into valuable therapeutic modalities for different diseases; however, there are many concerns about risk factors in human applications. NPs carry therapeutic chemicals that could improve the outcome of cancer therapies. Nowadays, NPs are being recognized as important and strategic agents in treatment of several disorders due to their unique properties in targeting malignant cells in tumor sites. Numerous investigations have shown that the majority of chemotherapeutic agents can be modified through entrapment in submicron colloidal systems. Still, there are problems and limitations in application of NPs in cancer therapy. The aim of the present study is to focus on potential NPs usage in cancer treatment with an emphasis on the cell cycle of malignant cells.     

Vertical distribution of benthic nematodes in an oligotrophic lake: seasonality, species and age segregation

The vertical distribution of nematodes up to 20 cm sediment depth was studied over a one-year period in the alpine, oligotrophic lake Königssee. Ten water depths were examined, four of which correspond to the littoral (1 m, 2 m, 5 m, 10 m), three to the littoriprofundal (15 m, 20 m, 30 m) and three to the profundal (60 m, 120 m, 190 m). The sediment was devided into four layers (0–2 cm, 2–5 cm, 5–10 cm and 10–20 cm). (1) The highest proportion of nematodes was found in the top layer. Out of 45 263 nematodes, 89% were found in the first 5 cm of the sediment and only 1 % deeper than 10 cm. (2) The proportion of nematodes in the top layer increased along with water depth. Water depth was a better predictor of percentage of nematodes in the top layer than particle size or content of organic carbon in the sediment. (3) There were considerable differences among species in their vertical distribution in the sediment. (4) There was a significant trend for juveniles to occupy more superficial layers than adults across various species. (5) There are time related vertical preferences among adults and juveniles of several nematode species across the year, suggesting vertical migration in the sediment (e.g. Aphanolaimus aquaticus Daday, Eumonhystera longicaudatula Gerlach & Riemann, Tobrilus gracilis Bastian, Monhystera paludicola de Man, Ethmolaimus pratensis de Man and Ironus tenuicaudatus de Man). The factors determining the vertical variation in nematode abundance in freshwater systems across space and time are still unknown.     

Effects of flow regulation, basin characteristics and land-use on macroinvertebrate communities in a large arid Patagonian river

Longitudinal distribution and abundance of macroinvertebrate communities were examined in relation to hydrochemical variables along the Chubut River in the Patagonian Precordillera and Plateau, Argentina. The Chubut River (>1000 km) is the largest river in the area and its basin is subject to multiple uses: agriculture, cattle raising, urbanization and the hydrological regime of the lower section is modified by a reservoir. Quantitative benthic samples were collected at 13 sites in the higher, middle and lower sections of the river basin. Sites were visited four times during 2004 and physicochemical parameters, chlorophyll a and particulate organic matter (POM) were assessed. Ninety-five taxa were collected in the study, with total species richness per site ranging from 5 to 51, and benthos density averaging 299–5024 ind m⁻². Altitude and turbidity were implicated as important factors determining macroinvertebrate assemblages along the river system, and an eutrophication gradient was documented in the regulated/urbanized section of the main river. High turbidity (TSS) and sedimentation limited algal productivity in the middle basin. Below the dam, TSS, total phosphorus (TP) and POM decreased, whereas soluble reactive phosphorus (SRP) and chlorophyll a increased. Macroinvertebrate density increased three fold in this area possibly due to habitat improvement and enhanced trophic resources. Mean species richness did not change below the impoundment; however the community was dominated by gastropods, chironomids and flatworms. The Chubut River is complex and its biotic community reflects the landscape attributes. While benthic composition and density was governed by turbidity and flood disturbance in some river segments, a greater environmental heterogeneity resulted in an unexpected high number of species at the main channel upper basin.     

Indirect effects of a parasite on a benthic community: an experiment with trematodes, snails and periphyton

1. Few studies have directly addressed the role played by parasites in the structure and function of ecosystems. Parasites influence the behaviour, reproduction and overall fitness of their hosts, but have been usually overlooked in community and ecosystem‐level studies. We investigated the effects of trematode parasites on snail–periphyton interactions. 2. Physa  acuta (Gastropoda: Pulmonata) snails infected with the trematode Posthodiplostomum minimum (often >30% of within‐shell biomass) grazed more rapidly than uninfected snails. Trematode effects on snail grazing indirectly affected the standing stock and community structure of periphyton. Populations of snails with 50% infected individuals reduced algal biomass by 20% more than populations with lesser (10% or 0%) infection rates. 3. The alga Cladophora glomerata dominated periphyton communities grazed by snail populations with 50% infection rates, whereas diatoms and blue–green algal taxa dominated when grazed by snail populations with lower infection rates. 4. Thus, trematodes indirectly affected periphyton communities by altering host snail behaviour, a trait‐mediated indirect effect. These results indicate that trematodes can indirectly influence benthic community structure beyond simple population fitness, with possible related effects on ecosystem function.     

The effects of predation and detritus on the structure of a stream insect community: a field test

Summary The role of predator density and plant detritus in determining patterns of insect abundance was tested in an Appalachian stream community (Reeds Creek, Pendleton Co, West Virginia). Insect colonization was followed over a 21-day period in field enclosures containing different densities of sculpins (Cottus bairdi and Cottus girardi). Sculpins caused no significant reductions in prey abundance; however, the combined effect of a guild of vertebrate predators caused a significant depression in the abundance of Chironomidae and the stonefly Leuctra. Since Chironomidae comprised approximately 85% of the total benthic fauna, vertebrate predation had an important role in the overall structure of the invertebrate community.Total insect abundance and diversity were correlated to the presence of plant detritus. However, this relationship was taxon specific, as abundance was highly correlated to detritus for only selected insect taxa. In general, abundance was best correlated with coarse particulate organic matter (CPOM), compared to fine particulate organic matter (FPOM) or total detritus (FPOM+CPOM+Whole leaf organic matter (LVOM)).This experiment illustrates that the influence of various potential structuring mechanisms is highly taxon dependent.     

Effects of two acanthocephalan species on the reproduction of Hyalella patagonica (Amphipoda, Hyalellidae) in an Andean Patagonian Lake (Argentina)

The aim of the present study was to evaluate alterations in the reproduction induced by acanthellae and cystacanths of the acanthocephalans Acanthocephalus tumescens and Corynosoma sp. in the amphipod Hyalella patagonica from Lake Mascardi. Specimens of H. patagonica were separated in two categories: paired amphipods (joined specimens during precopulatory mate guarding period until fertilization) and unpaired amphipods (alone specimens). Different analyses were performed: first with paired (n = 406) and unpaired (n = 375) amphipods, and second only with female amphipods (n = 1949), that were classified into three categories (without internal oocytes and eggs, only with internal oocytes, and with eggs). Also, carotenoid extraction was performed of amphipods uninfected (n = 75) and infected (n = 105) by cystacanths of Corynosoma sp. Unpaired amphipods had significantly higher prevalence of cystacanths of both acanthocephalan species than paired ones; but such differences were not found in prevalence of acanthellae. Female amphipods without internal oocytes and eggs showed significantly higher prevalence of cystacanths of both acanthocephalan species than the two other female categories; while females with eggs had significantly higher prevalence of A. tumescens acanthellae. Amphipods infected by Corynosoma sp. showed lower carotenoid concentration than uninfected ones. In Lake Mascardi, there is indirect evidence of both reduced mating success and female fecundity of H. patagonica provoked by both cystacanths species (A. tumescens and Corynosoma sp.). However, infections by acanthellae seem to have no effects.     

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。