Microorganisms play a key role for the functioning of healthy river ecosystems because they recycle nutrients and carbon from dead biomass (necromass), but little is known about how these fundamental processes are affected by multiple stressors such as increased temperature and salinity. In this study, we investigated the recycling of necromass by microorganisms in the river Boye before, during, and after a period of increased temperature and salinity using an outdoor flow-through system (ExStream). Rates of necromass recycling were measured as an increase in ¹³CO₂- concentration over time resulting from the microbial degradation of ¹³C -labelled necromass, which was offered either in the form of intact (but dead) or lysed E. coli cells. Preliminary results indicate that necromass recycling was highest in the first days of incubation, suggesting that it is an easily biodegradable carbon source. Interestingly, increased temperature strongly increased the rate of whole cell-necromass recycling compared to the unstressed control, while it slightly decreased the rate of lysed cell recycling. Increased salinity did not seem to affect necromass recycling alone or in combination with increased temperature. After stressor removal, necromass recycling rates were not distinguishable from the unstressed control. Overall, microbial necromass recycling is strongly affected by temperature but resistant to salinity stress, and the effect of temperature stress depends on necromass type. The fast recovery after stressor removal indicates high resilience of these microbial processes.

Primary Presenter: Una Hadžiomerović, University of Duisburg-Essen (UDE) (una.hadziomerovic@uni-due.de)

Authors:

Una Hadžiomerović, University of Duisburg-Essen (UDE)  (una.hadziomerovic@uni-due.de)

Rainer Meckenstock, University of Duisburg-Essen (UDE)  (rainer.meckenstock@uni-due.de)

Verena Brauer, University of Duisburg-Essen (UDE)  (verena.brauer@uni-due.de)

Iris Madge Pimentel, University of Duisburg-Essen (UDE)  (iris.madge-pimentel@uni-due.de)