Organic matter of terrigenous origin (t-OM) can represent a substantial contribution of allochthonous carbon to freshwater ecosystems. These inputs have intensified over the last few decades, in particular as a result of climate change. The intensification of t-OM fluxes combined with warming could deeply impact microbial heterotrophic activities in aquatic environments, and thus alter the capacity of these ecosystems to be sources or sinks of carbon. The amplitude and the persistence over time of such impacts, as well as the nature of the heterotrophic activities impacted, remain however poorly explored. Warming and t-OM enrichment were cross-simulated in 1000L-mesocosms filled with lake water, with a total of four conditions in triplicates: control (in situ natural water temperature), +t-OM, +6°C, both +t-OM and +6°C. The utilization pattern of different carbon substrates (© Biolog Ecoplates), coupled with bacterial abundance (flow cytometry), community respiration (O₂ optodes) and aminopeptidase exo-enzymatic activity (fluorogenic substrate analog) were measured over a 40-days experiment. The optical properties of the colored DOM (cDOM) was also followed over time and showed a clear t-OM signature on the initial OM pool until the end of the experiment. Warming, alone or combined with t-OM inputs, enhanced microbial activities (by a mean factor of 1.6 and 2.2 for aminopeptidase activity and community respiration, respectively), while bacterial abundances increased also in the +t-OM treatment. Bacteria used more carboxylic acids and polymers under higher temperature, with or without t-OM, while the t-OM inputs slightly enhanced the use of amines. We highlighted that t-OM inputs combined with warming not only impact the rate of organic matter utilization but also the diversity of substrates utilized, reflecting the degradation of the complex molecules composing the tDOM.

Primary Presenter: Dominique Lamy, Sorbonne University (dominique.lamy@sorbonne-universite.fr)

Authors:

Dominique Lamy, Institute of Ecology and Environmental Sciences of Paris (iEES-Paris), Sorbonne Université, Univ Paris Est Creteil, IRD, CNRS, INRA, Paris, France  (dominique.lamy@sorbonne-universite.fr)

Zoé Eglaine, Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Systematique Evolution, Gif-sur-Yvette, France  (zoe.eglaine@gmail.com)

Alex Abhaya, Institute of Ecology and Environmental Sciences of Paris (iEES-Paris), Sorbonne Université, Univ Paris Est Creteil, IRD, CNRS, INRA, Paris, France  (abhaya.alex@gmail.com)

Sarah Fiorini, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS, Saint-Pierre-les-Nemours, France  (sarah.fiorini@bio.ens.psl.eu)

Gérard Lacroix, Institute of Ecology and Environmental Sciences of Paris (iEES-Paris), Sorbonne Université, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS  (lacroix@bio.ens.psl.eu)

Alexis Millot, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS, Saint-Pierre-les-Nemours, France  (alexis.millot@biologie.ens.fr)

Philippe Catala, Laboratoire d’Océanographie Microbienne, Sorbonne Université, CNRS, Banyuls-sur-mer, France  (catala@obs-banyuls.fr)

Emile Laymand, Laboratoire d’Océanographie Microbienne, Sorbonne Université, CNRS, Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, Université des Antilles  (emile.laymand@obs-banyuls.fr)

Simon Chollet, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS, Saint-Pierre-les-Nemours, France  (simon.chollet@ens.fr)

Florent Massol, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS, Saint-Pierre-les-Nemours, France  (florent.massol@ens.fr)

Francis Dohou, Centre de Recherche en Écologie expérimentale et Prédictive et ECOTRON IdF (CEREEP ECOTRON IDF), CNRS, ENS, Saint-Pierre-les-Nemours, France  (francis.dohou@ens.fr)

Florence Hulot, Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Systematique Evolution, Gif-sur-Yvette, France  (florence.hulot@u-psud.fr)

Fabien Joux, Laboratoire d’Océanographie Microbienne, Sorbonne Université, CNRS, Banyuls-sur-mer, France  (fabien.joux@obs-banyuls.fr)