High content of phosphorus in leachates of the austral beech N. pumilio stimulates bacterioplankton C consumption

BALSEIRO, E.; DÍAZ VILLANUEVA, V.; BASTIDAS NAVARRO, M.; MODENUTTI, B.

Congreso; SAME 15; 2017

In North-Patagonian Andes, the austral beech Nothofagus pumilio determines the upper limit of the temperate forest and constitutes an important source of allochthonous DOM. In addition the wetlands of the area develop benthonic algal communities (Spirogyra sp and Zygnema sp) that provide autochthonous DOM. We aimed to analyze the differences in the nutritional quality of DOM for bacteria metabolism in a mountain lake located in North-Patagonia (Argentina). We performed experiments in which we analyze DOM lability and changes in bacterial communities in treatments enriched with algae exudates and N. pumilio leachates. We characterized DOM using spectrofluorometric analysis, and we assessed bacterial community composition using next-generation sequencing of the 16S rRNA gene. DOM characterization showed two protein-like (C1 and C5) and three humic-like components (C2, 3, and 4). In the enrichment with exudates C5 was more important, whereas in leachates the C1 and C4 dominated. Phosphorus content was higher in leachates, with a lower C: P ratio than exudates (197.4 ± 80.1 and 503.95± 105.8, respectively). The enrichments with leachates stimulated the bacterial metabolism, particularly during the first 2 days of incubation. In our experiments we observed the development of different bacteria assemblages likely due to changes in the C:P ratio of DOM in the enriched treatments and also in the different seasons. Our study demonstrated that high P relative content from allochthonous DOM stimulates the C-consumption, highlighting the importance of C: nutrient ratios in DOM as indicator of quality when analyzing C cycling in ecosystems.