Contrasting activation energies of litter-associated respiration and P uptake drive lower cumulative P uptake at higher temperatures

[摘要] Heterotrophic microbes play key roles in regulating fluxes ofenergy and nutrients, which are increasingly affected by globally changingenvironmental conditions such as warming and nutrient enrichment. While theeffects of temperature and nutrients on microbial mineralization of carbonhave been studied in some detail, much less attention has been given to howthese factors are altering uptake rates of nutrients. We used laboratoryexperiments to simultaneously evaluate the temperature dependence of solublereactive phosphorus (SRP) uptake and respiration by leaf-litter-associatedmicrobial communities from temperate headwater streams. Additionally, weevaluated the influence of the initial concentration of SRP on thetemperature dependence of P uptake. Finally, we used simple simulationmodels to extrapolate our results and estimate the effect of warming and Pavailability on cumulative gross uptake. We found that the temperaturedependence of P uptake was lower than that of respiration (0.48 vs. 1.02 eV). Further, the temperature dependence of P uptake increased with theinitial concentration of SRP supplied, ranging from 0.12 to 0.48 eV over an11 to 212  µ g L −1 gradient in initial SRP concentration.Finally, despite our laboratory experiments showing increases inmass-specific rates of gross P uptake with temperature, our simulationmodels predict declines in cumulative P uptake with warming, because theincreased rates of respiration at warmer temperatures more rapidly depletedbenthic carbon substrates and consequently reduced the biomass of thebenthic microbial community. Thus, even though mass-specific rates of P uptake were higher at the warmer temperatures, cumulative P uptake was lowerover the residence time of a pulsed input of organic carbon. Our resultshighlight the need to consider the combined effects of warming, nutrientavailability, and resource availability and/or magnitude on carbon processing asimportant controls of nutrient processing in heterotrophic ecosystems.

[学科分类] 大气科学