Contrasting dissolved organic matter biodegradation and bacterial cytometric features in oligotrophic and ultraoligotrophic Patagonian lakes

Abstract

Abstract Biodegradation process of dissolved organic matter (DOM) could be affected by its concentration and quality. Two biodegradation experiments were conducted in two contrasting seasons in two oligotrophic and one ultraoligotrophic temperate lakes, which comprise a natural gradient of dissolved organic carbon (DOC) concentration and quality (including lakes of < 83.33 μM). We examined associations between biodegradation and bacterial cytometric descriptors (i.e. abundance, DNA relative content, etc.) and with different DOM characteristics. The biolabile DOC (BDOC) was higher in shallow oligotrophic lakes, which displayed higher DOC concentration than the deep ultraoligotrophic one. The BDOC was mainly relatable not only to DOC concentration but also with DOM quality [fluorescent terrestrial-humic component normalized by DOC (C2:DOC), lignin content (a*350) and biological index]. We found a positive association between biodegradation process and high nucleic acid–content bacterial group. The bacterioplankton cytometric features were shaped by DOM concentration and quality along the biodegradation process. We concluded that in oligotrophic lakes, DOC concentration was the main driver of BDOC, whereas in ultraoligotrophic lakes, DOM quality played a more central role. This study contributes to better understand the biodegradation process in pristine low-DOC lakes with natural variation in allochthonous DOM inputs and with implications in the biogeochemical cycles.