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Saprotrophic fungi play important roles in transformations of carbon (C), nitrogen (N), and phosphorus (P) in aquatic environments. However, it is unclear how warming will alter fungal cycling of C, N, and P. We conducted an experiment with four aquatic hyphomycetes (Articulospora tetracladia, Hydrocina chaetocladia, Flagellospora sp. and Aquanectria penicillioides), and an assemblage of the same taxa, to test how temperature alters C and nutrient use. Specifically, we evaluated biomass accrual, C:N, C:P, δ13C, and C use efficiency (CUE) over a 35-d experiment with temperatures ranging from 4ºC to 20ºC. Changes in biomass accrual and CUE were predominantly quadratic with peaks between 7ºC and 15ºC. The C:P of H. chaetocladia biomass increased 9× over the temperature gradient, though the C:P of other taxa was unaffected by temperature. Changes in C:N were relatively small across temperatures. Biomass δ13C of some taxa changed across temperatures, indicating differences in C isotope fractionation. Additionally, the 4-species assemblage differed from null expectations based on the monocultures in terms of biomass accrual, C:P, δ13C, and CUE, suggesting that interactions among taxa altered C and nutrient use. These results highlight that temperature and interspecific interactions among fungi can alter traits affecting C and nutrient cycling. [ABSTRACT FROM AUTHOR]

Heterotrophic microbes play key roles in regulating fluxes of energy and nutrients, which are increasingly affected by globally changing environmental conditions such as warming and nutrient enrichment. While the effects of temperature and nutrients on microbial mineralization of carbon have been studied in some detail, much less attention has been given to how these factors are altering uptake rates of nutrients. We used laboratory experiments to simultaneously evaluate the temperature dependence of soluble reactive phosphorus (SRP) uptake and respiration by leaf-litter-associated microbial communities from temperate headwater streams. Additionally, we evaluated the influence of the initial concentration of SRP on the temperature dependence of P uptake. Finally, we used simple simulation models to extrapolate our results and estimate the effect of warming and P availability on cumulative gross uptake. We found that the temperature dependence of P uptake was lower than that of respiration (0.48 vs. 1.02 eV). Further, the temperature dependence of P uptake increased with the initial concentration of SRP supplied, ranging from 0.12 to 0.48 eV over an 11 to 212 µ g L -1 gradient in initial SRP concentration. Finally, despite our laboratory experiments showing increases in mass-specific rates of gross P uptake with temperature, our simulation models predict declines in cumulative P uptake with warming, because the increased rates of respiration at warmer temperatures more rapidly depleted benthic carbon substrates and consequently reduced the biomass of the benthic microbial community. Thus, even though mass-specific rates of P uptake were higher at the warmer temperatures, cumulative P uptake was lower over the residence time of a pulsed input of organic carbon. Our results highlight the need to consider the combined effects of warming, nutrient availability, and resource availability and/or magnitude on carbon processing as important controls of nutrient processing in heterotrophic ecosystems. [ABSTRACT FROM AUTHOR]

Leaf breakdown is an important process in forested headwater streams. A common method used to quantify the role of macroinvertebrate and microbial communities in leaf litter breakdown involves using paired mesh bags that either allow or exclude macroinvertebrate access to leaves. We examined common assumptions of the paired litterbag method to test (1) whether mesh size alters microbial respiration and (2) whether the effects of abrasive flows (e.g., from water and sediment) differ between coarse‐ and fine‐mesh litterbags. We measured rates of microbial respiration on Acer rubrum and Rhododendron maximum leaves incubated in coarse‐ and fine‐mesh litterbags. We also measured rates of abrasion using aerated concrete blocks in pairs of coarse‐ and fine‐mesh bags in ten streams across a gradient of discharge. We found that rates of microbial respiration on Acer rubrum leaves conditioned in fine‐mesh bags were 65% greater than the rates of respiration in paired coarse‐mesh bags, but respiration rates on Rhododendron maximum were similar in coarse‐ and fine‐mesh bags. Abrasion was, on average, 56% greater in coarse‐mesh than paired fine‐mesh bags, and these effects were greater in streams with higher discharge. These results suggest that more caution is required when attributing the difference in leaf breakdown between coarse‐ and fine‐mesh bags to macroinvertebrates. Because the effect of mesh size on microbial respiration of Acer leaves and abrasion are opposite in direction, the effect that dominates and creates bias likely depends on both environmental context and experimental design. [ABSTRACT FROM AUTHOR]

Functional traits of organisms, especially feeding traits, influence how organisms mediate ecosystem processes. As climate change, landscape modification and industrial waste heat release continue to increase water temperatures, shifts in the composition of feeding traits within aquatic macroinvertebrate communities may alter ecosystem processes. However, it is unclear whether thermal traits of macroinvertebrates vary systematically across functional feeding groups (FFGs; i.e., categories based on feeding ecology such as herbivores, shredders, predators, etc.) or phylogeny.We used previously published datasets on hundreds of macroinvertebrate taxa to evaluate how thermal traits differed across FFGs. We also examined the strength of phylogenetic signal in both FFG and thermal traits, using a new phylogeny of insect taxa. Then, we tested whether phylogenetic patterns offered a plausible explanation for differences in thermal traits among FFGs by comparing phylogenetic and non‐phylogenetic regressions.Shredders tended to have lower temperature preferences, optima and maxima (three of five of the thermal traits evaluated) than other FFGs. Patterns for other FFGs differed by thermal trait, but predators, collector‐gatherers and filterers had some of the highest thermal trait values. FFG explained 40% of the variation in critical thermal maximum, but <12% of the variation in the four other thermal traits.Phylogeny explained 26%–88% of the variation in thermal and feeding traits. For the subset of taxa and trait data that were available, phylogeny explained more than double the variation in thermal traits relative to FFG, but comparison of phylogenetic and non‐phylogenetic regressions highlighted that FFG explained variation in thermal traits that was independent of phylogeny.Our results highlight phylogeny and FFG as predictors of thermal traits in aquatic macroinvertebrates. Our results suggest that warmer water temperatures could favour predators, filterers and collector‐gatherers over shredders. Furthermore, our results confirm that certain orders of macroinvertebrates, such as Diptera, may be better suited to warmer temperatures than other orders, such as Plecoptera. [ABSTRACT FROM AUTHOR]

Heterotrophic microbes play key roles in regulating fluxes of energy and nutrients, which are increasingly affected by globally changing environmental conditions such as warming and nutrient enrichment. While the effects of temperature and nutrients on microbial mineralization of carbon have been studied in some detail, much less attention has been given to how these factors are altering uptake rates of nutrients. We used laboratory experiments to simultaneously evaluate the temperature dependence of soluble reactive phosphorus (SRP) uptake and respiration by leaf litter-associated microbial communities from temperate headwater streams. Additionally, we evaluated the influence of the initial concentration of SRP on the temperature dependence of P uptake. Finally, we used simple simulation models to extrapolate our results and estimate the effect of warming and P availability on cumulative gross uptake at the ecosystem level. We found that the temperature dependence of P uptake was lower than that of respiration (0.48 vs. 1.02 eV). Further, the temperature dependence of P uptake increased with the initial concentration of SRP supplied, ranging from 0.12–0.48 eV over a 11–212 µg L-1 gradient in initial concentrations. Finally, despite our laboratory experiments showing increases in mass-specific rates of gross P uptake with temperature, our simulation models found declines in cumulative P uptake with warming because the increased rates of respiration at warmer temperatures more rapidly depleted benthic carbon substrates and consequently reduced the biomass of the benthic microbial community. Thus, even though mass-specific rates of P uptake were higher at the warmer temperatures, cumulative ecosystem-level P uptake was lower over the residence time of a pulsed input of organic carbon. Our results highlight the need to consider the combined effects of warming, nutrient availability, and resource availability/magnitude on carbon processing as important controls of nutrient processing. [ABSTRACT FROM AUTHOR]

The majority of terrestrial net primary production decomposes, fueling detrital food webs and converting dead plant carbon to atmospheric CO2. There is considerable interest in determining the sensitivity of this process to climate warming. A common approach has been to use spatial gradients in temperature (i.e., latitude or elevation) to estimate temperature sensitivity. However, these studies typically relate decomposition rates to average temperatures at each site along such gradients, ignoring within-site temperature variation. To evaluate the potential effects of temperature variation on estimates of temperature sensitivity, we simulated plant litter decomposition using both randomly generated and real time series of temperature. This simulation approach illustrated how temperature variation leads to higher decomposition rates at a given mean temperature than is predicted from simulations in which temperature is held constant. Increases in decomposition rate were most evident at cooler sites, where temporal variation in temperature tends to be greater than at warmer sites. This unbalanced effect of temperature variation shifted the slope of the relationships between average temperature and decomposition rate, resulting in lower estimated temperature sensitivities than were used to simulate decomposition. For example, estimates of activation energy (Ea) were as much as 0.15 eV lower than the true Ea when decomposition was simulated with the true Ea set to the canonical respiration value of 0.65 eV. We found that the estimated Ea was lower than the true Ea for surface, soil, and air temperatures, but not for stream temperatures, for which there was only a weak relationship between temperature variation and mean temperature. Our results suggest that commonly used methods may underestimate the temperature dependence of litter decomposition, particularly in terrestrial environments. We encourage publication of temperature data that include variation estimates and suggest an alternative method for calculating temperature sensitivity that accounts for variation in temperature. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry uses information on a few key biological elements (C, N and P) to explain complex ecological patterns. Although factors driving variation in these elements are well established, expanding stoichiometric principles to explore dynamics of the many other essential elements comprising biological tissues (i.e. the ionome) is needed to determine their metabolic relationships and better understand biological control of elemental flows through ecosystems.In this paper, we report observations of ionomic variation in two species of salamander (Ambystoma opacum and A. talpoideum) across ontogenic stages using specimens from biological collections of two wetlands sampled over a 30‐year period. This unique data set allowed us to explore the extent of ionomic variation between species, among ontogenic stages, between sites and through time.We found species‐ and, to a lesser extent, site‐specific differences in C, N and P along with 13 other elements forming salamander ionomes but saw no evidence of temporal changes. Salamander ionomic composition was most strongly related to ontogeny with relatively higher concentrations of many elements in adult males (i.e. Ca, P, S, Mg, Zn and Cu) compared to metamorphic juveniles, which had greater amounts of C, Fe and Mn.In addition to patterns of individual elements, covariance among elements was used to construct multi‐elemental nutrient balances, which revealed differences in salamander elemental composition between species and sites and changes in elemental proportions across ontogenic development. These multi‐elemental balances distinguished among species‐site‐ontogenic stage groups better than using only C, N and P.Overall, this study highlights the responsiveness of consumer ionomes to life‐history and environmental variation while reflecting underlying relationships among elements tied to biological function. As such, ionomic studies can provide important insights into factors shaping consumer elemental composition and for predicting how these changes might affect higher‐order ecological processes. [ABSTRACT FROM AUTHOR]

Abstract Identifying freshwater systems that are at risk from anthropogenic stressors is a pressing management problem. In particular, the detection of metal pollution is often constrained by data availability and resources. To address this challenge and develop a tool to identify susceptible systems, we tested whether land cover could be predictive of stream sensitivity to metal pollution, as determined by the biotic ligand model (BLM). We used water chemistry data from the conterminous United States to estimate metal sensitivity in streams using two BLMs (i.e., HydoQual, Bio-Met). Subsequently, we combined the sensitivity estimates with land cover and physiochemical data from the GAGES-II database to build predictive models of sensitivity to metals in streams. When combined, our predictor variables (e.g., land cover, mean annual temperature, mean annual precipitation) generally explained about half of the variation in our dataset. In each model, the percent of wetlands in a watershed was strongly correlated with reduced sensitivity to metals, likely due to increased concentrations of dissolved organic carbon associated with wetlands. To validate the utility of the models, we used them to predict metal sensitivity in sites where metal concentrations had been collected, but where the full suite of BLM parameters were unknown. We were able to classify several hundred sites which are likely at risk to metal pollution. Our work highlights the value in considering metal toxicity at the landscape-scale and describes a new approach to estimate metal sensitivity when site-specific chemical parameters are unknown. Graphical abstract Image 1 Highlights • Metal pollution is linked to landscape process. • We explain a large portion of variation in metal sensitivity using geospatial data. • Wetland area within a watershed appears to buffer streams from metal contamination. [ABSTRACT FROM AUTHOR]

Active management practices to reduce or promote particular vegetation, known as vegetation treatments, are a common part of environmental management and they are conducted for a variety of purposes including wildfire risk mitigation, invasive species management, and ecological restoration. Vegetation treatment for wildfire mitigation in particular have increased dramatically in the Western United States in the past several decades. While vegetation treatments are common, data regarding the timing, location, and type of treatments conducted are often only maintained by the organization that conducted the work, hampering the ability of managers and researchers to understand the distribution and timing of vegetation treatments across a landscape. This dataset is a collection of spatially referenced records of vegetation treatments such as mechanical thinning, prescribed burning, and herbicide applications that were conducted in the state of New Mexico, USA and adjacent parts of Colorado, Oklahoma, and Texas. Spatial data were collected through requests to the regional or state offices for the relevant agencies (e.g., The Bureau of Land Management, the U.S. Forest Service, New Mexico State Forestry Division). The accuracy of this data collection approach was assessed by conducting more intensive data collection in five randomly selected focal watersheds across New Mexico. In these watersheds local offices of the larger agencies were contacted, as well as any smaller groups (e.g., soil and water conservation districts, municipalities, and environmental non-profits), and in person visits were made to gather any information on vegetation treatments possible. The overall dataset includes records of treatments spanning a century and includes records of 9.9 million acres of treatments conducted by more than a dozen different organizations. In the five focal watershed that we surveyed the database contained 7.4 % fewer acres of treated land than the more intensive interview approach. This spatially extensive dataset on vegetation treatments will be useful for researchers quantifying or modelling the effect of vegetation management on fire risk and behaviour. Additionally, this data will be useful to ecologists studying the distribution, movement, and habitat associations of a variety of plant an animal species. Finally, this data will be useful for research on landscape conservation and management., (© 2024 The Authors.)