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Lopez_Bianca (Ed.)
Rivers and streams contribute to global carbon cycling by decomposing immense quantities of terrestrial plant matter. However, decomposition rates are highly variable and large-scale patterns and drivers of this process remain poorly understood. Using a cellulose-based assay to reflect the primary constituent of plant detritus, we generated a predictive model (81% variance explained) for cellulose decomposition rates across 514 globally distributed streams. A large number of variables were important for predicting decomposition, highlighting the complexity of this process at the global scale. Predicted cellulose decomposition rates, when combined with genus-level litter quality attributes, explain published leaf litter decomposition rates with high accuracy (70% variance explained). Our global map provides estimates of rates across vast understudied areas of Earth and reveals rapid decomposition across continental-scale areas dominated by human activities.
Free, publicly-accessible full text available June 14, 2025 -
Summary To distinguish among hypotheses on the importance of resource‐exchange ratios in outcomes of mutualisms, we measured resource (carbon (C), nitrogen (N), and phosphorus (P)) transfers and their ratios, between
Pinus taeda seedlings and two ectomycorrhizal (EM) fungal species,Rhizopogon roseolus andPisolithus arhizus in a laboratory experiment.We evaluated how ambient light affected those resource fluxes and ratios over three time periods (10, 20, and 30 wk) and the consequences for plant and fungal biomass accrual, in environmental chambers.
Our results suggest that light availability is an important factor driving absolute fluxes of N, P, and C, but not exchange ratios, although its effects vary among EM fungal species. Declines in N : C and P : C exchange ratios over time, as soil nutrient availability likely declined, were consistent with predictions of biological market models. Absolute transfer of P was an important predictor of both plant and fungal biomass, consistent with the excess resource‐exchange hypothesis, and N transfer to plants was positively associated with fungal biomass.
Altogether, light effects on resource fluxes indicated mixed support for various theoretical frameworks, while results on biomass accrual better supported the excess resource‐exchange hypothesis, although among‐species variability is in need of further characterization.
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Abstract Producer–decomposer interactions within aquatic biofilms can range from mutualistic associations to competition depending on available resources. The outcomes of such interactions have implications for biogeochemical cycling and, as such, may be especially important in northern peatlands, which are a global carbon sink and are expected to experience changes in resource availability with climate change. The purpose of this study was to evaluate the effects of nutrients and organic carbon on the relative proportion of primary producers (microalgae) and heterotrophic decomposers (bacteria and fungi) during aquatic biofilm development in a boreal peatland. Given that decomposers are often better competitors for nutrients than primary producers in aquatic ecosystems, we predicted that labile carbon subsidies would shift the biofilm composition towards heterotrophy owing to the ability of decomposers to outcompete primary producers for available nutrients in the absence of carbon limitation.
We manipulated nutrients (nitrate and phosphate) and organic carbon (glucose) in a full factorial design using nutrient‐diffusing substrates in an Alaskan fen.
Heterotrophic bacteria were limited by organic carbon and algae were limited by inorganic nutrients. However, the outcomes of competitive interactions depended on background nutrient levels. Heterotrophic bacteria were able to outcompete algae for available nutrients when organic carbon was elevated and nutrient levels remained low, but not when organic carbon and nutrients were both elevated through enrichment.
Fungal biomass was significantly lower in the presence of glucose alone, possibly owing to antagonistic interactions with heterotrophic bacteria. In contrast to bacteria, fungi were stimulated along with algae following nutrient enrichment.
The decoupling of algae and heterotrophic bacteria in the presence of glucose alone shifted the biofilm trophic status towards heterotrophy. This effect was overturned when nutrients were enriched along with glucose, owing to a subsequent increase in algal biomass in the absence of nutrient limitation.
By measuring individual components of the biofilm and obtaining data on the trophic status, we have begun to establish a link between resource availability and biofilm formation in northern peatlands. Our results show that labile carbon subsidies from outside sources have the potential to disrupt microbial coupling and shift the metabolic balance in favour of heterotrophy. The extent to which this occurs in the future will probably depend on the timing and composition of bioavailable nutrients delivered to surface waters with environmental change (e.g. permafrost thaw).
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Abstract Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first
define each of the major C pools and fluxes and providerationale for their importance to wetland C dynamics. For each approach, we clarifywhat component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such aswhere andwhen an approach is typically used,who can conduct the measurements (expertise, training requirements), andhow approaches are conducted, including considerations on equipment complexity and costs. Finally, we reviewkey covariates andancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions. -
Abstract Periphyton communities associated with submerged plant detritus contain interacting autotrophic and heterotrophic microbes, and are sites of extracellular enzymatic activity. The strength and nature of these interactions might be expected to change over time as microbial communities develop on plant litter. Microbial interactions and enzymatic activity can be altered by nutrient availability, suggesting that litter stoichiometry could also affect these phenomena.
We grew wetland plants under ambient and nutrient‐enriched conditions to generate plant litter of differing nutrient content. In two experiments, we investigated: (1) the influence of algal photosynthesis on fungal and bacterial production and the activities of four extracellular enzymes throughout a 54‐day period of microbial colonisation and growth; and (2) the influence of litter stoichiometry on these relationships.
Ambient and nutrient‐enriched standing‐dead plant litter was collected and then submerged in wetland pools to allow for natural microbial colonisation and growth. Litter samples were periodically retrieved and transported to the laboratory for experiments manipulating photosynthesis using the photosystem II inhibitor DCMU (which effectively prevents algal photosynthetic activity). Algal (14C‐bicarbonate), bacterial (3H‐leucine), and fungal (14C‐acetate) production, and β‐glucosidase, β‐xylosidase, leucine aminopeptidase, and phosphatase activities (MUF‐ or AMC‐labelled fluorogenic substrates) were measured under conditions of active and inhibited algal photosynthesis.
Photosynthesis stimulated overall fungal and bacterial production in both experiments, although the strength of stimulation varied amongst sampling dates. Phosphatase activity was stimulated by photosynthesis during the first, but not the second, experiment. No other enzymatic responses to short‐term photosynthesis manipulations were observed.
Microbial communities on high‐nutrient litter occasionally showed increased extracellular enzyme activity, fungal growth rates, and bacterial production compared to communities on non‐enriched litter, but algal and fungal production were not affected. Litter stoichiometry had no effects on fungal, bacterial, or enzymatic responses to photosynthesis, but the mean enzyme vector analysis angle (a measure of P‐ versus N‐acquiring enzyme activity) was positively correlated to litter N:P, suggesting that elevated litter N:P led to an increase in the relative activity of P‐acquiring enzymes.
These results supported the hypothesis that algal photosynthesis strongly influences heterotrophic microbial activity on macrophyte leaf litter, especially that of fungi, throughout microbial community development. However, the strength of this photosynthetic stimulation does not generally depend on small differences in litter nutrient content.
Stimulation of microbial heterotrophs by algal photosynthesis could drive diurnal shifts in periphyton community and aquatic ecosystem function, as well as linking
green (photoautotroph‐based) andbrown (detrital‐based) food webs. -
Abstract In aquatic detrital‐based food webs, research suggests that autotroph‐heterotroph microbial interactions exert bottom‐up controls on energy and nutrient transfer. To address this emerging topic, we investigated microbial responses to nutrient and light treatments during
Liriodendron tulipifera litter decomposition and fed litter to the caddisfly larvaePycnopsyche sp. We measured litter‐associated algal, fungal, and bacterial biomass and production. Microbes were also labeled with14C and33P to trace distinct microbial carbon (C) and phosphorus (P) supportingPycnopsyche assimilation and incorporation (growth). Litter‐associated algal and fungal production rates additively increased with higher nutrient and light availability. Incorporation of microbial P did not differ across diets, except for higher incorporation efficiency of slower‐turnover P on low‐nutrient, shaded litter. On average,Pycnopsyche assimilated fungal C more efficiently than bacterial or algal C, andPycnopsyche incorporated bacterial C more efficiently than algal or fungal C. Due to high litter fungal biomass, fungi supported 89.6–93.1% ofPycnopsyche C growth, compared to 0.2% to 3.6% supported by bacteria or algae. Overall,Pycnopsyche incorporated the most C in high nutrient and shaded litter. Our findings affirm others' regarding autotroph‐heterotroph microbial interactions and extend into the trophic transfer of microbial energy and nutrients through detrital food webs.