Planktonic community rescue under herbicide pollution: the driving factors and ecological consequences

Community rescue enables ecological communities to persist under otherwise lethal environmental stress through adaptive changes. The present study addresses what community attributes may predict the chance of rescue, and the ecological consequences associated with community rescue. Replicate aquatic microcosms were set up from each of 20 base planktonic communities, and were exposed to a gradient of concentrations of an herbicide. Planktonic respiration rate was measured as a surrogate of community activity, to infer the potential of community rescue. We found that the rescue potential depended on planktonic taxonomical composition but not diversity per se. We then studied in detail planktonic communities that rescued from a specific high concentration of herbicide pollution. Community rescue was accompanied with multiple ecological costs, including reduced taxonomical diversity and primary productivity, as well as simplified planktonic interaction networks. A shift from producer-dominated toward decomposer-dominated taxa was observed; specifically, certain heterotrophic bacteria and fungi became more abundant at the expense of microalgae. A number of taxa highly resistant to glyphosate were identified. Our results highlight that community rescue under severe herbicide pollution may be associated with unwanted ecological costs, and studies of this kind may help to search for microbial taxa capable of pollutant biodegradation.