Genetic and extracellular enzyme survey of planktonic communities of aquatic habitats in Green Lakes Valley, 2017

Preliminary work done in the soils of Green Lakes Valley (GLV) has shown that the microbial communities are generally carbon and phosphorus limited. While most working examining nutrient limitations in GLV has focused on the terrestrial environment, the aquatic environments lack the same study. Longterm monitoring of the lakes in GLV show that there are shifts in carbon availability (quantity and quality) over course of the Colorado alpine growing season. These shifts have been attributed to changes in the source of DOC as snow packs melt out and flow rates decline in the valley altering the ratio of internal (autochthonous) to external (allochthonous) carbon input to the lakes. We examined the links between the biogeography of planktonic communities and the functional response of those communities to shifting nutrient limitations to test the idea that nutrient limitation and composition of planktonic communities are linked both temporally and spatially in GLV. We determined the composition of GLV’s planktonic communities using amplicon sequencing of the small ribosomal subunit sequences (16S, 18S rDNA) and determined nutrient limitations using extracellular enzyme activity (EEA) assays to examine if communities shifted in conjunction with shifts in EEA. We observed that shifting composition in the planktonic communities of GLV mirrored shifts in nutrient limitation (primarily carbon and phosphorus limitation) over the course of the alpine growing season. Alpine and sub-alpine lakes showed opposite trends in the EEA of carbon acquisition enzymes while all lakes showed high activity for phosphorus acquisition enzymes. The planktonic communities were consistently phosphorus limited throughout the study, but carbon limitation was relieved in the alpine lakes as the season progressed while sub-alpine lakes became more carbon limited. The most likely mechanism behind the observed shifts in carbon limitation are the previously studied shifts where DOC is sourced in the valley as water flow paths and intensity change over the course of the alpine growing season.