Biodiversy can differ substantially among a set of engineered ecosystems, even when those ecosystems are designed with the same engineering objective in mind. Whether differences in biodiversity translate into differences in engineering performance, however, is under active debate. Theoretical considerations predict that communities with more biodiversity are more likely to contain strains that have positive effects on the rates of particular ecosystem functions, thus resulting in positive associations between those two variables. However, if communities were sufficiently biodiverse to nearly saturate the set of possible positive effects, then positive associations would not occur between biodiversity and the rates of particular ecosystem functions. To test these expectations, we measured the taxonomic biodiversity, functional biodiversity, and rates of 10 different micropollutant biotransformations for 10 full-scale wastewater treatment plant communities. We then tested for associations between biodiversity and engineering performance.
We demonstrated that biodiversity is positively associated with the rates of some (but not all) micropollutant biotransformations. Thus, one cannot assume whether or how biodiversity will associate with the rate of any particular micropollutant biotransformation. We further demonstrated that the strongest positive association is between biodiversity and the collective rates of multiple micropollutant biotransformations. Thus, more biodiversity is likely required to maximize the collective rates of multiple micropollutant biotransformations than is required to maximize the rate of any individual micropollutant biotransformation. We finally provide evidence that the positive associations are stronger for rare micropollutant biotransformations than for common micropollutant biotransformations. Together, our results are consistent with the hypothesis that differences in biodiversity can indeed translate into differences in the performance of engineered ecosystems.