Stream water column samples from nine Mediterranean freshwater ecosystems Other. Stream water column samples from nine Mediterranean freshwater ecosystems

In this study we explore how heterotrophic NO3 uptake in freshwater ecosystems is influenced by (1) DOC concentration and DOC:NO3 stoichiometry, (2) DOM composition and reactivity and (3) explore the extent to which the taxonomical and functional composition of the microbial community and their enzymatic activity could influence NO3 uptake and associated DOC consumption. To do so, we conducted laboratory incubations of water from nine freshwater ecosystems (eight streams and one wetland) draining catchments with different land uses to maximize the range of DOC:NO3 ratios and DOM characteristics. For microbial community composition, we characterized, in each site, the microbial community before starting the incubation by filtering 500 mL of water through 0.2 micrometers polycarbonate membranes. This procedure was performed in triplicate for each site. Each filter was stored in a 2 mL Eppendorf with 0.5 mL lysis buffer and frozen at -20 C degrees until subsequent DNA extraction. DNA was extracted using the DNeasy PowerSoil kit (QIAGEN) following the manufacturer's instructions, and the purified DNA was sequenced following the methods of the Research Technology Support Facility at Michigan State University.