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Nutrient uptake, storage, and release are critical ecosystem functions that affect carbon processing and food web dynamics. Yet, mechanisms controlling when ecosystems are net sinks or sources of nutrients are uncertain. Specifically, how nutrient supply ratios alter rates and ratios of net nutrient uptake and release is unclear. To assess whether net nitrogen (N) and phosphorus (P) uptake and release are linked to supply N:P, we experimentally enriched five forest streams at different N:P (target molar N:P range 2:1–128:1) for 2 years. We quantified net nutrient exchange (NNE) as the difference between the expected N and P fluxes assuming conservative transport (background concentrations plus experimental inputs) and the observed nutrient fluxes at the downstream end of each experimental stream reach. Supply N:P did not affect the magnitude of NNE for either N or P, but the likelihood of net N and P uptake was greatest at intermediate N:P supply (N:P = 99:1 and 55:1, respectively). Streams appeared to be highly flexible in their N:P uptake and release; the slopes between NNEN and NNEP within each stream increased with supply N:P. Furthermore, slopes comparing supply N:P to uptake and release N:P were near one (0.98 ± 0.06 SE and 0.82 ± 0.13 SE, respectively), indicating a high degree of flexibility. Overall, we found greater stoichiometric flexibility than has been shown in short-term nutrient-addition experiments. We suggest that this flexibility results from changes in nutrient recycling within biofilms or changes in community structure, which may take longer to manifest than the duration of shorter-term experiments. [ABSTRACT FROM AUTHOR]

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]

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]