Functional and compositional responses of stream microphytobenthic communities to multiple stressors increase and decrease
My project is taking place within the framework of the Collaborative Research Centre (CRC) 1439: Multilevel Response to Stressors Increase and release in Stream ecosystems (RESIST). RESIST is an interdisciplinary research project that aims to study the effect of multiple stressors (such as salinity, temperature, land use and hydrology) on the trophic network and particular organism groups. The results will be used to model possible effects of the impending climate change.
In my research I am investigating the effect of multiple stressors on microphytobenthos, mainly diatoms, and photosynthesis-related traits in both mesocosm experiments and fieldwork analyses. Very few studies reported the effects of anthropogenic stressors upon photosynthetic fitness and performance of stream microphytobenthic communities up to date. In addition, an integrative characterization of changes in community composition and photosynthesis‐related traits accompanying stressor load and release under highly controlled conditions has been very seldom attempted.
My Ph.D. research project aims to fill this gap by assessing compositional responses of benthic diatoms (using digital microscopy and DNA metabarcoding) in parallel with functional changes, e.g., photosynthesis‐related traits, of microphytobenthic communities to stressors, including flow velocity, salinity, and temperature, increase and release in the large-scale ExStream mesocosm experimental setting (Fig. 1). To decide on which salinity level could be used as one of the stressors in the actual ExStream mesocosm experiments to be run in the next 2 years, a pre-experiment was conducted in 2021 to test the effect of different salinity levels (100, 200, 300, 400, 500, 600, 700 mg/l NaCl versus background) on microphytobenthos. Preliminary amplicon sequencing data analysis of biofilm samples collected in the 2021 ExStream pre-experiment shows no clear trends in protistan community composition with salinity, but diatoms analysis on virtual slides (digital microscopy, Fig. 2) is still ongoing. However, PERMANOVA revealed a large difference from the control (background salinity level) for the 200 and 700 mg/l NaCl treatments. These observations will help us to better plan the upcoming ExStream experiments in 2022 and 2023.
Figure 1. ExStream large-scale experimental setting
Figure 2. Annotation of diatoms on virtual slides using BIIGLE (Bio-Image Indexing and Graphical Labelling Environment, find it on www.biigle.de)