Leaf litter decomposition in an intermittent stream: channel vs. riparian area (original) (raw)
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Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream
The Science of the total environment, 2018
Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of β-glucosidase, cellobiohydrolase and phosphatase were gradually red...
Annual patterns of litter decomposition in the channel and riparian areas of an intermittent stream
Aquatic Ecology, 2021
Intermittent streams, dominant in arid and semi-arid regions, are suggested to be more representative of the global river network than perennial rivers. Even so, the impacts of constant changes in hydrological regime on the functioning of these streams and riparian areas remain to be elucidated. In this study, two native deciduous litter species were used to compare microbialdecomposition patterns between the channel of an intermittent stream and its riparian area over one year. Overall, the stream channel presented higher decomposition rates and fungal biomass than the riparian area, for both litter species. Despite a prolonged absence of streambed surface water (254 days), differences in hydrological conditions in the wetter seasons (autumn and winter) led to lingering effects, shaping and differentiating decomposition dynamics in both zones throughout the whole hydrological cycle. As the present results highlight the importance of the "hydrological imprint" for the leaves degradation process, long term studies seem to be advisable over short-term ones to better understand the functioning of intermittent streams.
Applied and Environmental Microbiology, 2013
into open-land streams, whereas tree litter is predominant in forested streams. We set out to elucidate whether the activity and structure of microbial communities on decomposing leaves are determined by litter quality (i.e., grass or tree leaves colonized) or whether changes during riparian succession affecting litter standing stocks on the stream bed play an overriding role. We used 15 outdoor experimental streams to simulate changes in litter supplies reflecting five stages of riparian succession: (i) a biofilm stage with no litter, (ii) an open-land stage characterized by grass litter inputs, (iii) a transitional stage with a mix of grass and tree litter, (iv) an early forested stage with tree litter, and (v) an advanced forested stage with 2.5 times the amount of tree litter. Microbial activities on tree (Betula pendula) and grass (Calamagrostis epigejos) litter were unaffected by either the quantity or type of litter supplied to the experimental streams (i.e., litter standing stock) but differed between the two litter types. This was in stark contrast with bacterial and fungal community structure, which markedly differed on grass and tree litter and, to a lesser extent, also among streams receiving different litter inputs. These patterns reveal distinct responses of microbial community structure and activity to the bulk litter available in streams but consistent responses to the litter type colonized.
Litter diversity, fungal decomposers and litter decomposition under simulated stream intermittency
Functional Ecology, 2011
1. The drying of stream channels resulting from flow interruption is expected to increase as a consequence of climate change. Implications for aquatic organisms and processes are profound. We assessed whether riparian diversity can partially buffer against consequences of drying on fungal decomposers and leaf litter decomposition, an important ecosystem process. 2. Our central hypothesis was that during dry periods recalcitrant leaf litter with high waterholding capacity would extend the window of opportunity for microbial activity in less recalcitrant litter when both litter types are mixed, and that this would lead to a positive litter diversity effect on decomposition. To test for such interactive effects, we conducted a diversity experiment in a Mediterranean stream, in which alder and oak litter, and a mixture of both, was subjected to various drying regimes differing in intensity and timing. 3. Drying regime affected both fungal decomposers and the decomposition rate of alder litter. Effects were observed both immediately and 3 weeks after stream flow resumed. Small differences in the timing of the dry period influenced both decomposition rate and measures of fungal performance (i.e. biomass and sporulation activity). Litter mixing, in contrast, had no effect on either decomposition or fungal decomposers, although mixing increased moisture retention in alder litter as required for the mechanism hypothesized to lead to a diversity effect. 4. Given the contrasting traits of the litter types used in the experiment, our results imply that riparian tree diversity is unlikely to buffer against increased frequencies of stream flow disruption expected in the face of climate change. It appears, however, that the precise timing of dry periods and high-flow events will strongly influence the extent to which stream food webs can exploit the resources supplied by riparian vegetation in the form of leaf litter.
Hydrobiologia, 2017
The present study aims to understand how microbial decomposition of leaf litter from two riparian tree species differing in their quality varies among streams covering a gradient of nutrient concentrations. We incubated leaf litter from alder (Alnus glutinosa) and sycamore (Platanus 9 hispanica) in 3 streams with low human pressure and 2 streams influenced by wastewater treatment plant effluents. We quantified leaf litter decomposition rates (k) and examined the temporal changes in the leaf litter concentrations of carbon (C) and nitrogen (N) throughout the incubation period. We measured the extracellular enzyme activities involved in degradation of C (i.e., cellobiohydrolase) and organic phosphorus (i.e., phosphatase). Results showed that alder k decreased with increasing nutrient concentrations, while sycamore decomposed similarly among streams. For both species, leaf litter N concentrations were positively related to in-stream dissolved N concentrations. However, we found different temporal patterns of leaf litter N concentrations between species. Finally, we found relevant differences in the enzymatic activities associated to each leaf litter species across the nutrient gradient. These results suggest that the intrinsic characteristics of the leaf litter resources may play a relevant role on the microbially driven leaf litter decomposition and mediate its response to dissolved nutrient concentrations across streams.
Fungal importance extends beyond litter decomposition in experimental early-successional streams
Environmental Microbiology, 2012
Fungi are important decomposers of leaf litter in streams and may have knock-on effects on other microbes and carbon cycling. To elucidate such potential effects, we designed an experiment in outdoor experimental channels simulating sandbottom streams in an early-successional state. We hypothesized that the presence of fungi would enhance overall microbial activity, accompanied by shifts in the microbial communities associated not only with leaf litter but also with sediments. Fifteen experimental channels received sterile sandy sediment, minimal amounts of leaf litter, and one of four inocula containing either (i) fungi and bacteria, or (ii) bacteria only, or (iii) no microorganisms, or (iv) killed microorganisms. Subsequently, we let water from an early-successional catchment circulate through the channels for 5 weeks. Whole-stream metabolism and microbial respiration associated with leaf litter were higher in the channels inoculated with fungi, reflecting higher fungal activity on leaves. Bacterial communities on leaves were also significantly affected.
Freshwater …, 2010
1. Leaf litter constitutes the major source of organic matter and energy in woodland stream ecosystems. A substantial part of leaf litter entering running waters may be buried in the streambed as a consequence of flooding and sediment movement. While decomposition of leaf litter in surface waters is relatively well understood, its fate when incorporated into river sediments, as well as the involvement of invertebrate and fungal decomposers in such conditions, remain poorly documented. 2. We tested experimentally the hypotheses that the small interstices of the sediment restrict the access of the largest shredders to buried organic matter without compromising that of aquatic hyphomycetes and that fungal decomposers in the hyporheic zone, at least partly, compensate for the role of invertebrate detritivores in the benthic zone. 3. Alder leaves were introduced in a stream either buried in the sediment (hyporheic), buried after 2 weeks of exposure at the sediment surface (benthic-hyporheic), or exposed at the sediment surface for the entire experiment (benthic). Leaf decomposition was markedly faster on the streambed surface than in the two other treatments (2.1-and 2.8-fold faster than in the benthic-hyporheic and hyporheic treatments, respectively). 4. Fungal assemblages were generally less diverse in the hyporheic habitat with a few species tending to be relatively favoured by such conditions. Both fungal biomass and sporulation rates were reduced in the hyporheic treatment, with the leaves subject to the benthic-hyporheic treatment exhibiting an intermediate pattern. The initial 2-week stage in the benthic habitat shaped the fungal assemblages, even for leaves later subjected to the hyporheic conditions. 5. The abundance and biomass of shredders drastically decreased with burial, except for Leuctra spp., which increased and was by far the most common leaf-associated taxon in the hyporheic zone. Leuctra spp. was one of the rare shredder taxa displaying morphological characteristics that increased performance within the limited space of sediment interstices. 6. The carbon budgets indicated that the relative contributions of the two main decomposers, shredders and fungi, varied considerably depending on the location within the streambed. While the shredder biomass represented almost 50% of the initial carbon transformed after 80 days in the benthic treatment, its contribution was <0.3% in the hyporheic one and 2.0% in the combined benthic-hyporheic treatment. In contrast, Correspondence: Julien Cornut, Laboratoire d'écologie fonctionnelle, 2541 mycelial and conidial production in the permanently hyporheic environment accounted for 12% of leaf mass loss, i.e. 2-3 times more than in the two other conditions. These results suggest that the role of fungi is particularly important in the hyporheic zone. 7. Our findings indicate that burial within the substratum reduces the litter breakdown rate by limiting the access of both invertebrate and fungal decomposers to leaves. As a consequence, the hyporheic zone may be an important region of organic matter storage in woodland streams and serve as a fungal inoculum reservoir contributing to further dispersal. Through the temporary retention of litter by burial, the hyporheic zone must play a significant role in the carbon metabolism and overall functioning of headwater stream ecosystems.
Aquatic Microbial Ecology, 2014
Aquatic fungi and bacteria have long been recognized as key drivers in ecosystem processes such as leaf litter decomposition. We examined fungal and bacterial communities on decaying alder Alnus glutinosa (L.) Gaertner leaves along a gradient of increasing agricultural land use and associated nutrient enrichment in 9 boreal streams during 4 separate seasons (fall 2003, spring 2005, fall 2005, and spring 2006). Denaturing gradient gel electrophoresis (DGGE) and quantitative polymerase chain reactions (qPCR) showed that agricultural land use had significant effects on both bacterial and fungal communities, and on the ratios of fungi to total microbes associated with decomposing leaf litter. Furthermore, landscape factors and fluvial geomorphology appeared to influence the community composition of fungi and bacteria. Seasonal effects were found for fungal community structure only, indicating a higher temperature sensitivity of fungi compared to bacteria.
Contribution of Stream Detrivores, Fungi, and Bacteria to Leaf Breakdown Based on Biomass Estimates
Ecology, 2002
Linking species and ecosystems is currently one of the great challenges in ecology. To this end, we assess here the contributions of bacteria, fungi, and detritivorous invertebrates (shredders) to leaf litter breakdown, a key ecosystem-level process. We enclosed alder (Alnus glutinosa) and willow (Salix fragilis) leaves in coarse-mesh bags (5 g dry mass), placed them in a stream during peak leaf fall, and retrieved them periodically to determine leaf mass remaining and the biomass of leaf-associated organisms. Shredder biomass was derived from numbers and length-mass relationships, bacterial numbers and biomass were determined by epifluorescence microscopy, and fungal biomass was measured as ergosterol. In addition, conidial production of aquatic hyphomycetes was determined. Leaves decomposed rapidly with exponential breakdown coefficients k of 0.035 d-' (alder) and 0.027 d-1 (willow). Leaves were also quickly colonized within the first 4 wk of decomposition, when shredder biomass reached 263 and 141 mg dry mass/litter bag, respectively. Maximum bacterial numbers (5.6 and 4.8 X 1010 g-' detrital dry mass) were attained after 8 wk and corresponded to a biomass of 3.6 (alder) and 3.1 (willow) mg dry mass/g, <5% of the maximum fungal biomass (77 and 70 mg dry mass/g, respectively). Aquatic hyphomycetes released up to 2.7 and 1.4 X 106 conidia-g-'d -', equivalent to a daily conidial production of 9.4 and 2.9 mg dry mass/g on alder and willow, respectively. Calculations based on the measured decomposer biomass and conidial production, published microbial growth efficiencies, turnover times, and shredder feeding rates indicate that shredders accounted for the largest portion of overall leaf mass loss (64% and 51 % on alder and willow leaves, respectively), fungi contributed at least 15% and 18%, and bacterial contribution also was estimated to be substantial (7% and 9%). Analyses of elemental flows from allochthonous leaf litter thus clearly require a quantitative consideration of the complex decomposer consortium responsible for leaf decomposition.