Mechanisms and thresholds of fungicide effects on microbial communities and organic matter processing
Final Report Abstract
In the first project phase, we examined the effects of fungicides on organic matter processing in streams. We found that the fungicide toxicity gradient in the field study was associated with changes in microbial communities and a decline in microbial organic matter processing. In the second project phase that is presented here, we scrutinised the effect mechanisms of fungicides on microbial communities and the potential propagation to organic matter processing. In addition, we reconciled the mismatch regarding threshold levels between field observations and the few studies on fungicides under controlled conditions (e.g. microcosms, mesocosms). In the first work package, we scrutinised the effect mechanisms of fungicides on microbial leaf processing. The experiment followed a complex test design that considered crucial elements of the field situation, namely repeated exposure, feeding pressure by shredders and multiple cycles of colonisation-decomposition. The experiment was conducted in four regions worldwide using typical invertebrate shredders and leaves (a consortium of laboratories from Australia, Germany, Denmark, and Sweden) and employed an exposure pattern with mixtures derived from a global analysis of fungicide concentrations in surface waters. In addition, the experiment featured three turnovers of organic matter in terms of leaf material, to examine potential adaptation or accumulation of effects. We detected an initial reduction in leaf decomposition with similar recovery times across regions. Despite a similar functional response, the response of the fungal communities differed across regions. Morphological identification and molecular methods (i.e. metabarcoding) produced similar results regarding the composition of fungal communities. The second work package aimed to establish a stronger link between fungicide toxicity and potential changes in microbial communities and organic matter processing. It featured a field study with ten streams along a gradient of fungicide toxicity, where one pristine upstream site at the edge of the forest and one downstream site in the viticultural area were selected (i.e. a total of 20 sites). The field survey spanned over the pre-fungicide, the fungicide and the post-fungicide application period and included the comparison of microbial communities and microbial processing between upstream and downstream sites. Using sets of leaf bags from pristine upstream and viticultural downstream reaches as well as those that were colonised in pristine reaches and then translocated to downstream reaches, we detected differences in (1) fungal community composition and organic matter decomposition across different seasons and intensities of fungicide application, (2) fungal communities based on the location of substrate colonisation as well as an interaction effect on the decomposition of the season with the location of substrate colonisation. Our results indicate that the fungal communities in sites with high fungicide application recover outside the main fungicide application period. Overall, this follow-up project provides a mechanistic explanation of how fungal communities respond to fungicides and further evidence of the causality of fungicide toxicity driving fungal community assembly in agricultural stream systems.
Publications
- 2018. Similar recovery time of microbial functions from fungicide stress across biogeographical regions. Scientific Reports 8, 17021
Schreiner, V.C., Feckler, A., Fernández, D., Frisch, K., Muñoz, K., Szöcs, E., Zubrod, J.P., Bundschuh, M., Rasmussen, J.J., Kefford, B.J., Axelsen, J., Cedergreen, N., Schäfer, R.B.
(See online at https://doi.org/10.1038/s41598-018-35397-1)
