AME 83:147-159 (2019)  -  DOI: https://doi.org/10.3354/ame01908

ABSTRACT: Suspended particulate matter (SPM) samples collected in the Rhône River were incubated in vitro at different salinities, and the degradation of terrestrial vascular plant material was monitored using specific lipid tracers (triterpenes, cuticular waxes and phenolic acids). Two samplings were compared, i.e. during and after a phytoplankton bloom in the river (potamoplankton). Degradation was observed at a salinity close to that of seawater. Changes in salinity allow for the establishment of specific bacterial communities comprising bacteria possessing a capacity to degrade algal and vascular plant components more efficiently than those initially present within the river. The presence of potamoplankton clearly enhanced the mineralization of vascular plant material. The potamoplankton algal material was intensively degraded during the incubations and could thus act as a co-substrate or induce the appearance of a bacterial community efficiently degrading terrestrial vascular plants. In SPM samples collected in the salinity gradient of the Rhône Estuary, bacterial degradation of vascular plant material increased with the proportion of algal sterols, strongly suggesting the involvement of a priming effect. Bacterial diversity analyses showed the dominance of Betaproteobacteria in freshwater and Alphaproteobacteria and Gammaproteobacteria in seawater. These results revealed the importance of potamoplankton and of the structure of bacterial communities during the degradation of terrestrial vascular plant material in estuaries.

KEY WORDS: Estuaries · Terrestrial organic matter · Vascular plants · Biodegradation · Salinity · Potamoplankton