Environmental degradation results in contrasting changes in the assembly processes of stream bacterial and fungal communities

Environmental degradation may have strong effects on community assembly processes. We examined the assembly of bacterial and fungal communities in anthropogenically altered and near‐pristine streams. Using pyrosequencing of bacterial and fungal DNA from decomposed alder Alnus incana leaves, we specifically examined if environmental degradation deterministically decreases or increases the compositional turnover of bacterial and fungal communities. Our results showed that near‐pristine streams and anthropogenically altered streams supported distinct fungal and bacterial communities. The mechanisms assembling these communities were different in near‐pristine and altered environments. Environmental disturbance homogenized bacterial communities, whereas fungal communities were more dissimilar in disturbed sites than in near‐pristine sites. Compositional variation of both bacteria and fungi was related to water chemistry variables in disturbed sites, further implying the influence of environmental degradation on community assembly. Bacterial and fungal communities in near‐pristine streams were weakly controlled by environmental factors, suggesting that the relative importance of niche‐based versus neutral processes in assembling microbial communities may strongly depend on the spatial scale and local environmental context. Our results thus suggest that environmental degradation may strongly affect the composition and β‐diversity of stream microbial communities colonizing leaf litter, and that the direction of the change can be different between bacteria and fungi. A better understanding of the environmental tolerances of microbes and the mechanisms assembling microbial communities in natural environmental settings is needed to predict how environmental alteration is likely to affect microbial communities.     

Effects of burial on leaf litter quality,microbial conditioning and palatability to three shredder taxa

Summary 1. Heterotrophic microorganisms are crucial for mineralising leaf litter and rendering it more palatable to leaf‐shredding invertebrates. A substantial part of leaf litter entering running waters may be buried in the streambed and thus be exposed to the constraining conditions prevailing in the hyporheic zone. The fate of this buried organic matter and particularly the role of microbial conditioning in this habitat remain largely unexplored. 2. The aim of this study was to determine how the location of leaf litter within the streambed (i.e. at the surface or buried), as well as the leaf litter burial history, may affect the leaf‐associated aquatic hyphomycete communities and therefore leaf consumption by invertebrate detritivores. We tested the hypotheses that (i) burial of leaf litter would result in lower decomposition rates associated with changes in microbial assemblages compared with leaf litter at the surface and (ii) altered microbial conditioning of buried leaf litter would lead to decreased quality and palatability to their consumers, translating into lower growth rates of detritivores. 3. These hypotheses were tested experimentally in a second‐order stream where leaf‐associated microbial communities, as well as leaf litter decomposition rates, elemental composition and toughness, were compared across controlled treatments differing by their location within the streambed. We examined the effects of the diverse conditioning treatments on decaying leaf palatability to consumers through feeding trials on three shredder taxa including a freshwater amphipod, of which we also determined the growth rate. 4. Microbial leaf litter decomposition, fungal biomass and sporulation rates were reduced when leaf litter was buried in the hyporheic zone. While the total species richness of fungal assemblages was similar among treatments, the composition of fungal assemblages was affected by leaf litter burial in sediment. 5. Leaf litter burial markedly affected the food quality (especially P content) of leaf material, probably due to the changes in microbial conditioning. Leaf litter palatability to shredders was highest for leaves exposed at the sediment surface and tended to be negatively related to leaf litter toughness and C/P ratio. In addition, burial of leaf litter led to lower amphipod growth rates, which were positively correlated with leaf litter P content. 6. These results emphasise the importance of leaf colonisation by aquatic fungi in the hyporheic zone of headwater streams, where fungal conditioning of leaf litter appears particularly critical for nutrient and energy transfer to higher trophic levels.     

Microbial community composition but not diversity changes along succession in arctic sand dunes

The generality of increasing diversity of fungi and bacteria across arctic sand dune succession was tested. Microbial communities were examined by high‐throughput sequencing of 16S rRNA genes (bacteria) and internal transcribed spacer (ITS) regions (fungi). We studied four microbial compartments (inside leaf, inside root, rhizosphere and bulk soil) and characterized microbes associated with a single plant species (Deschampsia flexuosa) across two sand dune successional stages (early and late). Bacterial richness increased across succession in bulk soil and leaf endosphere. In contrast, soil fungal richness remained constant while root endosphere fungal richness increased across succession. There was, however, no significant difference in Shannon diversity indices between early and late successional stage in any compartment. There was a significant difference in the composition of microbial communities between early and late successional stage in all compartments, although the major microbial OTUs were shared between early and late successional stage. Co‐occurrence network analysis revealed successional stage‐specific microbial groups. There were more co‐occurring modules in early successional stage than in late stage. Altogether, these results emphasize that succession strongly affects distribution of microbial species, but not microbial diversity in arctic sand dune ecosystem and that fungi and bacteria may not follow the same successional trajectories.     

Application of Fungal and Bacterial Production Methodologies to Decomposing Leaves in Streams

As leaves enter woodland streams, they are colonized by both fungi and bacteria. To determine the contribution of each of these microbial groups to the decomposition process, comparisons of fungal and bacterial production are needed. Recently, a new method for estimating fungal production based on rates of [(sup14)C]acetate incorporation into ergosterol was described. Bacterial production in environmental samples has been determined from rates of [(sup3)H]leucine incorporation into protein. In this study, we evaluated conditions necessary to use these methods for estimating fungal and bacterial production associated with leaves decomposing in a stream. During incubation of leaf disks with radiolabeled substrates, aeration increased rates of fungal incorporation but decreased bacterial production. Incorporation of both radiolabeled substrates by microorganisms associated with leaf litter was linear over the time periods examined (2 h for bacteria and 4 h for fungi). Incorporation of radiolabeled substrates present at different concentrations indicated that 400 nM leucine and 5 mM acetate maximized uptake for bacteria and fungi, respectively. Growth rates and rates of acetate incorporation into ergosterol followed similar patterns when fungi were grown on leaf disks in the laboratory. Three species of stream fungi exhibited similar ratios of rates of biomass increase to rates of acetate incorporation into ergosterol, with a mean of 19.3 (mu)g of biomass per nmol of acetate incorporated. Both bacterial and fungal production increased exponentially with increasing temperature. In the stream that we examined, fungal carbon production was 11 to 26 times greater than bacterial carbon production on leaves colonized for 21 days.     

Microbial leaf degraders in boreal streams: bringing together stochastic and deterministic regulators of community composition

1. Leaves that fall into the water represent a new habitat for microorganisms to colonise in streams, providing an opportunity to study colonisation and the subsequent regulation of community structure. We explored community composition of bacteria and fungi on decomposing alder leaves in nine streams in central Sweden, and describe their relationship with environmental variables. Succession of the microbial community was studied in one of the streams for 118 days. Microbial community composition was examined by denaturing gradient gel electrophoresis on replicate samples of leaves from each stream. 2. During succession in one stream, maximum taxon richness was reached after 34 days for bacteria and 20 days for fungi respectively. Replicate samples within this stream differed between each other earlier in colonisation, while subsequently such variation among replicate communities was low and remained stable for several weeks. Replicate samples taken from all the nine streams after 34 days of succession showed striking similarities in microbial communities within‐streams, although communities differed more strongly between streams. 3. Canonical analysis of microbial communities and environmental variables revealed that water chemistry had a significant influence on community composition. This influence was superimposed on a statistical relationship between the properties of stream catchments and microbial community composition. 4. The catchment regulates microbial communities in two different ways. It harbours the species pool from which the in‐stream microbial community is drawn and it governs stream chemistry and the composition of organic substrates that further shape the communities. We suggest that there is a random element to colonisation early in succession, whereas other factors such as species interactions, stream chemistry and organic substrate properties, result in a more deterministic regulation of communities during later stages.     

Diversity,role in decomposition,and succession of zoosporic fungi and straminipiles on submerged decaying leaves in a woodland stream

Leaf litter is a very important primary source of energy in woodland streams. Decomposition of leaf litter is a process mediated by many groups of microorganisms which release extracellular enzymes for the degradation of complex macromolecules. In this process, true fungi and straminipiles are considered to be among the most active groups, more active than the bacteria, at least during the early stages of the process. Colonization increases the quality of the leaves as a food resource for detritivores. In this way, matter and energy enter detritus-based food chains. Previously, aquatic hyphomycetes were considered to be the major fungal group responsible for leaf litter decomposition. Although zoosporic fungi and straminipiles are known to colonize and decompose plant tissues in various environments, there is scant information on their roles in leaf decomposition. This study focuses on the communities of zoosporic fungi and straminipiles in a stream which are involved in the decomposition of leaves of two plant species, Ligustrum lucidum and Pouteria salicifolia, in the presence of other groups of fungi. A characteristic community dominated by Nowakowskiella elegans, Phytophthora sp., and Pythium sp. was found. Changes in the fungal community structure over time (succession) was observed: terrestrial mitosporic fungi appeared during the early stages, zoosporic fungi, straminipiles, and aquatic Hyphomycetes in early-to-intermediate stages, while representatives of the phylum Zygomycota were found at early and latest stages of the decomposition. These observations highlight the importance of zoosporic fungi and straminipiles in aquatic ecosystems.     

The Role of Early Fungal Colonizers in Leaf‐Litter Decomposition in Portuguese Streams Impacted by Agricultural Runoff

We conducted a transplant experiment between two streams in NW Portugal impacted by agricultural runoff, mainly differing in phosphate concentration, to determine whether fungi on decomposing leaves would adapt to the new environment or would be replaced by fungi of the recipient stream. The most nutrient enriched stream had lower fungal diversity but faster leaf decomposition. Leaf transplantation did not alter fungal activity or species dominance. Multidimensional scaling ordination of fungal communities, from DNA fingerprint or conidial production, revealed that transplanted communities resembled more those of the original stream than the recipient stream. Results suggest that early fungal colonizers will determine the development and activity of fungal communities on decomposing leaves in streams impacted by agricultural practices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.     

Phagotrophic protists are a key component of microbial communities processing leaf litter under contrasting oxic conditions

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Response of Aquatic Leaf Associated Microbial Communities to Elevated Leachate DOC: A Microcosm Study

In Central Europe climate change will increase summer droughts, which cause both, premature leaf fall and fragmentation of small streams during summer and early autumn. As a consequence dissolved organic carbon (DOC) leached from leaves will be dispersed into pools with long water residence time. A microcosm experiment was performed to test the effect of high concentrations of leachate DOC and the relative importance of labile and refractory leachate compounds on leaf associated microbial parameters. In microcosms leaf discs colonized in a stream were exposed to high concentrations of either leaf leachate, glucose or tannic acid. Leaf associated respiration, fungal sporulation, leaf mass loss and fungal biomass (ergosterol) were measured during a 3 weeks experimental period and compared to control without DOC amendment. The results imply that depending on source and composition elevated leachate DOC may have variable effects on microbial mediated litter decomposition. Our findings suggest reduced microbial decomposition rates in pools of fragmented streams receiving premature leaf fall. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Does mixing litter of different qualities alter stream microbial diversity and functioning on individual litter species?

We examined effects of leaf litter quality and species mixing on microbial community diversity and litter processing in a forested headwater stream. Single- and mixed-species litter from dominant tree species ( Liriodendron tulipifera , Acer rubrum , Quercus prinus , Rhododendron maximum ) were incubated in a southern Appalachian headwater stream. Litter carbon-to-nitrogen ratios (C:N), mass loss, microbial respiration, and microbial community diversity were analyzed on individual litter species after incubation. Initial C:N varied widely among individual litter species, and these differences persisted throughout the 50-day incubation period. Litter C:N of the recalcitrant species R. maximum remained higher than that of all other litter species, and C:N of R. maximum and L. tulipifera increased when both species were present together in a mixture. Although mass loss of individual species was generally unaffected by mixing, microbial respiration was greater on A. rubrum and Q. prinus litter incubated with R. maximum compared to either species alone. Enhanced resource heterogeneity, which was experimentally achieved by litter mixing low- and higher-quality litter species, resulted in apparent shifts in microbial community diversity on individual litter species. Responses of bacterial and fungal community diversity to litter mixing varied among individual litter species. Our results suggest that changes in tree species composition in riparian forests and subsequent changes in litter resource heterogeneity could alter stream microbial community diversity and function. As bacteria and fungi are important decomposers of plant litter in aquatic ecosystems, resource-dependent changes in microbial communities could alter detrital processing dynamics in streams.     

Towards a budget of leaf litter decomposition in a first-order woodland stream

To construct a budget of carbon transformations occurring during leaf decomposition, alder leaves were placed in a woodland stream, later retrieved at weekly intervals, and rates of fungal and bacterial production, microbial respiration, and release of dissolved organic matter (DOM) and fine particulate organic matter (FPOM) were determined during short laboratory incubations. Carbon dioxide was the major decomposition product, explaining 17% of the microbially mediated leaf mass loss. DOM and FPOM were also important products (5 and 3% of total mass loss, respectively), whereas carbon flow to microbial biomass was low (2%). Fungal biomass in leaves always exceeded bacterial biomass (95–99% of total microbial biomass), but production of bacteria and fungi was similar, indicating that both types of microorganisms need to be considered when examining leaf decomposition in streams. Comparison of leaf mass loss in coarse and fine mesh bags revealed, in addition, that the shredder, Gammarus pulex, had a major impact on leaf decomposition in this study.     

Effect of Inorganic Nutrients on Relative Contributions of Fungi and Bacteria to Carbon Flow from Submerged Decomposing Leaf Litter

The relative contributions of fungi and bacteria to carbon flow from submerged decaying plant litter at different levels of inorganic nutrients (N and P) were studied. We estimated leaf mass loss, fungal and bacterial biomass and production, and microbial respiration and constructed partial carbon budgets for red maple leaf disks precolonized in a stream and then incubated in laboratory microcosms at two levels of nutrients. Patterns of carbon flow for leaf disks colonized with the full microbial assemblage were compared with those colonized by bacteria but in which fungi were greatly reduced by placing leaf disks in colonization chambers sealed with membrane filters to exclude aquatic hyphomycete conidia but not bacterial cells. On leaves colonized by the full microbial assemblage, elevated nutrient concentrations stimulated fungi and bacteria to a similar degree. Peak fungal and bacterial biomass increased by factors of 3.9 and 4.0; cumulative production was 3.9 and 5.1 times higher in the high nutrient in comparison with the low nutrient treatment, respectively. Fungi dominated the total microbial biomass (98.4 to 99.8%) and cumulative production (97.3 and 96.5%), and the fungal yield coefficient exceeded that of bacteria by a factor of 36 and 27 in low- and high-nutrient treatments, respectively. Consequently, the dominant role of fungi in leaf decomposition did not change as a result of nutrient manipulation. Carbon budgets indicated that 8% of leaf carbon loss in the low-nutrient treatment and 17% in the high-nutrient treatment were channeled to microbial (essentially fungal) production. Nutrient enrichment had a positive effect on rate of leaf decomposition only in microcosms with full microbial assemblages. In treatments where fungal colonization was reduced, cumulative bacterial production did not change significantly at either nutrient level and leaf decomposition rate was negatively affected (high nutrients), suggesting that bacterial participation in carbon flow from decaying leaf litter is low regardless of the presence of fungi and nutrient availability. Moreover, 1.5 and 2.3 times higher yield coefficients of bacteria in the reduced fungal treatments at low and high nutrients, respectively (percentage of leaf carbon loss channeled to bacterial production), suggest that bacteria are subjected to strong competition with fungi for resources available in leaf litter.     

Fungal and Bacterial Colonization of Submerged Leaf Litter in a Mediterranean Stream

Microbial colonization dynamics of fungi and bacteria were analyzed in an intermittent Mediterranean forested stream using two different leaf substrata (Platanus acerifolia and Populus nigra). Results showed that fungal and bacterial biomass accumulation was stimulated on both leaves due to a flooding episode that increased dissolved inorganic nitrogen (DIN) and dissolved oxygen (DO) availability in the stream water. Leaf mass loss coincided with the parallel increase in microbial biomass and extracellular enzymatic activities after the flood event. Differences in litter quality favoured bacterial biomass accumulation and β‐glucosidase and cellobiohydrolase enzymatic activities in the soft Populus species. Microbial heterotrophs colonization of submerged leaf litter and organic matter use in Mediterranean‐type streams are modulated by environmental conditions, especially the hydrological variability. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fungal endophyte‐infected leaf litter alters in‐stream microbial communities and negatively influences aquatic fungal sporulation

Endophytes are ubiquitous plant‐associated microbes and although they have the potential to alter the decomposition of infected leaf litter, this has not been well‐studied. The endophyte Rhytisma punctatum infects the leaves of Acer macrophyllum (bigleaf maple), causing the appearance of black ‘tar spots’ that persist in senesced leaves. Other foliar fungi also cause visible damage in healthy tissues of this host plant system including an unidentified bullseye‐shaped lesion, common in western Washington. Using three treatments of endophyte infection status in leaf tissue (R. punctatum‐infected, bullseye‐infected, lesion‐free), leaf litter discs were submerged in a third‐order temperate stream using mesh litter bags and harvested periodically over two months to determine the effects of litter treatment and incubation time on litter mass loss, fungal sporulation, and microbial community colonization. Litter containing symptomatic endophyte infections (Rhytisma or bullseye) had reduced sporulation of aquatic hyphomycetes, but decomposed significantly faster than lesion‐free or bullseye‐infected litter. Using amplicon‐based sequencing, we found a significant difference in bacterial communities colonizing Rhytisma‐infected and bullseye‐infected leaf litter, a significant difference in fungal communities colonizing Rhytisma‐infected leaf litter compared to the two other treatments, and a change in both community structure and relative abundances of bacterial and fungal taxa throughout the study period. Indicator Species Analysis clarified the drivers of these community shifts at the genus level. Our results show that endophyte‐associated, in‐stream sporulation and microbial community effects are observable within one species of leaf litter.     

Comparison of Fungal Activities on Wood and Leaf Litter in Unaltered and Nutrient-Enriched Headwater Streams

Fungi are the dominant organisms decomposing leaf litter in streams and mediating energy transfer to other trophic levels. However, less is known about their role in decomposing submerged wood. This study provides the first estimates of fungal production on wood and compares the importance of fungi in the decomposition of submerged wood versus that of leaves at the ecosystem scale. We determined fungal biomass (ergosterol) and activity associated with randomly collected small wood (<40 mm diameter) and leaves in two southern Appalachian streams (reference and nutrient enriched) over an annual cycle. Fungal production (from rates of radiolabeled acetate incorporation into ergosterol) and microbial respiration on wood (per gram of detrital C) were about an order of magnitude lower than those on leaves. Microbial activity (per gram of C) was significantly higher in the nutrient-enriched stream. Despite a standing crop of wood two to three times higher than that of leaves in both streams, fungal production on an areal basis was lower on wood than on leaves (4.3 and 15.8 g C m⁻² year⁻¹ in the reference stream; 5.5 and 33.1 g C m⁻² year⁻¹ in the enriched stream). However, since the annual input of wood was five times lower than that of leaves, the proportion of organic matter input directly assimilated by fungi was comparable for these substrates (15.4 [wood] and 11.3% [leaves] in the reference stream; 20.0 [wood] and 20.2% [leaves] in the enriched stream). Despite a significantly lower fungal activity on wood than on leaves (per gram of detrital C), fungi can be equally important in processing both leaves and wood in streams.     

Leaf litter decomposition and microbial activity in nutrient-enriched and unaltered reaches of a headwater stream

SUMMARY 1. Decomposition of red maple ( Acer rubrum ) and rhododendron ( Rhododendron maximum ) leaves and activity of associated microorganisms were compared in two reaches of a headwater stream in Coweeta Hydrologic Laboratory, NC, U.S.A. The downstream reach was enriched with ammonium, nitrate, and phosphate whereas the upstream reach was not altered.
2. Decomposition rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher for both leaf types in the nutrient-enriched reach. Species richness and community structure of aquatic hyphomycetes also exhibited considerable changes with an increase in the number of fungal codominants in the nutrient-enriched reach.
3. Fungal biomass was one to two orders of magnitude greater than bacterial biomass in both reaches. Changes in microbial respiration rate corresponded to those in fungal biomass and sporulation, suggesting a primary role of fungi in leaf decomposition.
4. Nutrient enrichment increased microbial activity, the proportion of leaf carbon channelled through the microbial compartment and the decomposition rate of leaf litter.     

The influence of water chemistry on the enzymatic degradation of leaves in streams

1. Aquatic hyphomycetes degrade leaf litter in both softwater and hardwater streams. During growth on leaves, these fungi secrete an array of extracellular polysaccharidases that are differentially affected by pH. Hydrolytic enzymes exhibit acidic pH optima, whereas pectin lyases have neutral to alkaline pH optima. 2. Enzyme activities associated with microbial communities colonizing yellow poplar (Liriodendron tulipifera) leaves submerged in an acidic (pH 6.3), softwater stream were compared with those occurring in an alkaline (pH 8.2), hardwater stream. In addition to pH differences, the hardwater stream had higher nutrient concentrations and higher temperatures than the softwater stream. Conditions in the hardwater stream favoured greater microbial growth, fungal activity, rates of leaf breakdown and softening. However, activities of hydrolytic enzymes (xylanase, endocellulase, galacturonanase) were lower in the hardwater stream than in the softwater stream. Consequently, activities of these hydrolytic enzymes were not good indicators of leaf breakdown in these streams. 3. In contrast, the activities of pectin lyase were higher in the hardwater stream than in the softwater stream, corresponding to the greater rates of leaf breakdown and softening that occurred in the hardwater stream. These results support previous findings that pectin lyase is closely associated with the softening and maceration of leaf detritus and suggest that pectin degradation is a key process in the initial stages of leaf breakdown.     

Respiration and annual fungal production associated with decomposing leaf litter in two streams

1. We compared fungal biomass, production and microbial respiration associated with decomposing leaves in one softwater stream (Payne Creek) and one hardwater stream (Lindsey Spring Branch). 2. Both streams received similar annual leaf litter fall (478–492 g m^?2), but Lindsey Spring Branch had higher average monthly standing crop of leaf litter (69 ± 24 g m^?2; mean ± SE) than Payne Creek (39 ± 9 g m^?2). 3. Leaves sampled from Lindsey Spring Branch contained a higher mean concentration of fungal biomass (71 ± 11 mg g^?1) than those from Payne Creek (54 ± 8 mg g^?1). Maximum spore concentrations in the water of Lindsay Spring Branch were also higher than those in Payne Creek. These results agreed with litterbag studies of red maple (Acer rubrum) leaves, which decomposed faster (decay rate of 0.014 versus 0.004 day^?1), exhibited higher maximum fungal biomass and had higher rates of fungal sporulation in Lindsey Spring Branch than in Payne Creek. 4. Rates of fungal production and respiration per g leaf were similar in the two streams, although rates of fungal production and respiration per square metre were higher in Lindsey Spring Branch than in Payne Creek because of the differences in leaf litter standing crop. 5. Annual fungal production was 16 ± 6 g m^?2 (mean ± 95% CI) in Payne Creek and 46 ± 25 g m^?2 in Lindsey Spring Branch. Measurements were taken through the autumn of 2 years to obtain an indication of inter‐year variability. Fungal production during October to January of the 2 years varied between 3 and 6 g m^?2 in Payne Creek and 7–27 g m^?2 in Lindsey Spring Branch. 6. Partial organic matter budgets constructed for both streams indicated that 3 ± 1% of leaf litter fall went into fungal production and 7 ± 2% was lost as respiration in Payne Creek. In Lindsey Spring Branch, fungal production accounted for 10 ± 5% of leaf litter fall and microbial respiration for 13 ± 9%.     

Warming water and leaf litter quality but not plant origin drive decomposition and fungal diversity in an experiment

The fungi associated with leaf litter play a key role in decomposition and can be affected both by the warming water and the invasion of non-native species in riparian vegetation. Warming water and invasion of non-native riparian species on stream fungal communities have been studied mainly in temperate ecosystems. We tested the effects of warming water and non-native plant Psidium guajava on leaf litter decomposition, conidia density, species richness and beta diversity of tropical stream fungi. Thus, we carried out an experiment using the current mean temperature of streams from northwestern Paraná in South Brazil (22 °C) and two temperatures above the current mean temperature (26 °C and 29 °C). We also used the leaves of a non-native plant (P. guajava), and two native plants (one of similar nutritional quality, and the other of higher nutritional quality than the non-native species) occurring in Neotropical streams riparian vegetation. Warming water accelerated leaf litter decomposition and reduced conidia density and fungal richness in native and non-native plants. However, species composition and beta diversity were not affected by water temperature. Our study showed that warming affects the fungi of streams, the main microorganisms responsible for decomposition and that the nutritional quality of the leaves may be more important than the origin of riparian plant species. Despite this, further investigations should be conducted on the interaction of P. guajava with the flow of nutrients in these environments and how it can affect other ecosystem processes and the food chain. Efforts to study the effects of water warming and biological invasion on the attributes and distribution of fungi in streams are vital, making them a tool for the conservation of riparian ecosystems.