Spatial and temporal patterns in carbon, nitrogen, and phosphorus composition of leaf-associated microbes in southern Appalachian streams

Multi-element assessments aid our understanding of nutrient cycling and limitation in stream systems. In this study, we ask 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. Sugar maple leaf packs were incubated in 5 study streams (southwestern Virginia and western North Carolina) spanning a gradient in streamwater N:P ratios (DIN:SRP ~2 to 200) during fall/winter 2008-2009. Leaf packs were collected simultaneously from all sites at multiple time intervals for analysis of microbial biomass C, N, and P composition. 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. These structure-function relationships address the implications of microbe elemental composition to ecosystem-scale N and P dynamics in streams.