Microbes are responsible for the primary uptake of inorganic nutrients in ecosystems and play an important role in mediating coupled elemental cycles. In this study, we addressed the implications of microbe elemental composition to ecosystem-scale N and P dynamics in streams. Specifically, we asked how the carbon (C), nitrogen (N), and phosphorus (P) composition of stream microbes associated with leaves vary spatially and temporally and how this variation translates to whole-stream uptake of N and P. Red maple leaf packs were deployed for microbial colonization in the fall/winter in 5 study streams (southwestern Virginia and western North Carolina) spanning a gradient in streamwater N:P ratios (DIN:SRP ~2 to 200). Leaf packs were collected sequentially from all sites. Chloroform fumigation extraction methods, developed primarily in soils and adapted for stream biofilms, were used to determine microbial C, N, and P composition. Whole-stream solute releases were executed incrementally with ammonium, nitrate, and phosphate to estimate uptake metrics of N and P. Uptake metrics from solute releases were compared with relative abundance of C, N, and P derived from microbial biomass of conditioned leaves collected from these sites.  

Results/Conclusions

Microbial C, N, and P composition, estimated via chloroform fumigation methods, varied across the 5 sites. Generally, microbial biomass with high C:nutrient content was associated with streams of low nutrient concentrations and low N:P. Furthermore, microbial elemental composition (C:nutrient biomass ratios) varied with whole-stream nutrient uptake metrics of N and P, suggesting implications of microbial stoichiometric structure to ecosystem-scale N and P dynamics in streams.