Dataset used in:
"Organic matter composition and water stoichiometry are main drivers of heterotrophic nitrate uptake in Mediterranean headwater streams."

by: Xavi Peñarroya, Núria Catalán, Anna Freixa, Anna Lupon, Xavier Triadó-Margarit, Eugènia Martí, Montserrat Soler, Emili O. Casamayor, Susana Bernal.

This dataset provide the results of an incubation experiment conducted during spring 2021. In this study, we investigated the kinetics of heterotrophic NO3- uptake in 9 Mediterranean freshwater ecosystems, mainly headwater streams. To do so, we conducted laboratory incubations for 23 days and characterised water chemistry, DOM composition (using spectroscopic indices) and degradation (using a Reactivity Continuum model), as well as microbial community composition and functioning by analysing the potential abundance of N-cycling genes and extracellular enzymatic activities. Our results revealed that NO3- uptake rates (kNO3) were positively related with DOC:NO3 ratios (r2 = 0.4) and to NO3:SRP ratios (r2 = 0.6). Furthermore, kNO3 was negatively correlated to the humification index (r2 = 0.7), suggesting that a higher proportion of humic-like compounds slows down heterotrophic NO3- uptake. A partial least squares regression model (PLS) pinpointed that water stoichiometry, DOM composition and reactivity, and microbial composition and activity collectively contributed to explain the variability in kNO3 observed across sites.

The dataset provided includes water chemistry, DOM spectroscopy, extracellular enzyme activity and microbial composition and functional prediction of the water from each of the study sites prior to the incubation experiments. The dataset also includes nitrate uptake rates, DOC and oxygen consumption rates, and variables extracted from the Reactivity Continuity model measured during the incubation experiments.

The nucleotide sequence data in Figure 3 have been uploaded in electronic format to the NCBI Sequence Read Archive, available via BioProject ID PRJNA1131982.

Data to reproduce the PLS model shown in Figure 7 are provided in Table S1 of the manuscript.