Transformation of organic carbon in the terrestrial-aquatic interface
Final Report Abstract
A deeper knowledge of aquatic organic carbon transformation, its physical and the microbial key player are of high relevance for the modelling of carbon flow through landscapes and for the understanding of the global carbon cycle. The results gained from this project significantly improve our understanding of mechanisms involved in regulation of organic carbon transformation in aquatic and semiaquatic ecosystems with emphasis on ephemeral streams and its sediment structure. Consequently, they contribute to a better understanding of the relevance and the understanding of organic carbon mineralisation and involved microbial community composition in regards to different sediment strata and patches across those ecosystems. Significant progress could be obtained on three different aspects: Firstly, the relevance of recalcitrant terrestrial organic carbon in respect to microbial assimilation and mineralization has been further clarified. We provide new insight into how different mechanisms are pronounced/ control the contribution of fungi and bacteria in aquatic carbon cycling in relation to the composition of the organic matter pool. Using a 13C stable-isotope approach we combined for the first time continuous measurements of carbon mineralization with the analysis of microbial phospholipids to link microbial activities to relative changes in the abundance of fungal and bacterial heterotrophs. Elucidation of the relationship between organic matter quality and microbial activities is fundamental to improve our understanding on how freshwater ecosystems interact with the global carbon cycling. Thus our study adds valuable information to this field of research. Secondly, effects of periodic sediment shifting occurring in migrating sand ripples were investigated in regard to microbial carbon mineralization and different carbon qualities in microcosm experiments. We could show for the first time that the mechanical disturbance in migrating ripples modulates the sedimentassociated microorganisms affecting its structure and functions. Change in regimen from stable to migrating ripple sediment and vise-versa, showed a different structure-function response that depended on age of the biofilm. However, further experiments are needed to clarify the role of structural variability of biofilms to its response to periodic migrating and further on the regulating factors during the transition from stable to migrating. Finally, we conducted stable isotope tracer study in experimental outdoor streams with different scenarios. We manipulated algal abundance using different light intensities and aimed at examining how their relevance for leaf litter metabolism by stream biofilms relates to variations in streambed heterogeneity, droughts and rewetting’s. We show for the first time that cycling of terrestrial carbon in benthic biofilms is shaped by streambed heterogeneity. Our findings provide evidence that a higher solute transfer may reduce spatial barriers between biofilm organisms and thus enhance the metabolic interactions among microbial auto- and heterotrophs. Accordingly, our study has profound implications for the previously postulated effects of autochthonous carbon on terrestrial carbon decomposition in stream ecosystems and, therefore, greatly adds to current research on microbial turnover of terrestrial carbon in aquatic ecosystems. Moreover, our study provides knowledge on resistance and resilience of temperate microbial communities to drought and rewetting and linking these to shading and sediment structure. The experiment provided also evidence that despite these shifts, stream metabolic functions were highly resilient and modulated by shading. Thus, our results suggest that sediment structure alterations and riparian vegetation are strong modulators of stream metabolism and should be regarded in management preparing temperate streams to predicted drought stress.
Publications
- (2018) Shading and sediment structure effects on stream metabolism resistance and resilience to infrequent droughts. The Science of the total environment 621 1233–1242
Zlatanović, Sanja; Fabian, Jenny; Premke, Katrin; Mutz, Michael
(See online at https://doi.org/10.1016/j.scitotenv.2017.10.105) - (2016). Untangling Hyporheic Residence time Distributions and Whole Stream Metabolism Using a Hydrological Process Model. Procedia Engineering, 154, 1071-1078
Altenkirch, N., Zlatanovic, S., Woodward, K. B., Trauth, N., Mutz, M., & Molkenthin, F.
(See online at https://doi.org/10.1016/j.proeng.2016.07.598) - (2017). Fungal-bacterial dynamics and their contribution to terrigenous carbon turnover in relation to organic matter quality. ISME J
Fabian J., Zlatanovic S, Mutz M., Premke K.
(See online at https://doi.org/10.1038/ismej.2016.131) - (2017). Importance of advective mass transfer and sediment surface area for streambed microbial communities. Freshwater Biology, 62(1), 133-145
Mendoza‐Lera, C., Frossard, A., Knie, M., Federlein, L. L., Gessner, M. O., & Mutz, M.
(See online at https://doi.org/10.1111/fwb.12856) - (2017). Periodic sediment shift in migrating ripples influences benthic microbial activity, Water Resour. Res., 53
Zlatanovic, S., J. Fabian, C. Mendoza-Lera, K. Benjamin Woodward, K. Premke, and M. Mutz
(See online at https://doi.org/10.1002/2017WR020656) - (2018) Environmental control on microbial turnover of leaf carbon in streams–ecological function of phototrophic-heterotrophic interactions. Frontiers in microbiology 9 104
Fabian J., Zlatanovic S, Mutz M., Grossart H-P, van Geldern R, Gleixner G and Premke K
(See online at https://doi.org/10.3389/fmicb.2018.01044)
