Biodiversity and disease risk in an algal biofuel system: An experimental test in outdoor ponds using a before-after-control-impact (BACI) design

because with the exception of a moderate increase in average water temperature (S3 Fig in S1 Appendix), there were no other biologically significant changes detected among the replicate ponds between the Before and After fungal infection periods (Section Physical and chemical conditions of raceways). Moreover, the small magnitude of difference in average water temper- ature is still within optimal temperature for algae production, and thus is unlikely the cause of such a drastic decrease in productivity [42]. Additionally, no significant effect of biodiversity on the response measured in feedstock production metrics to fungal infection was found (Sec- tions Areal productivity, Biomass stability, and Maximum biomass yield). This can be seen in Fig 2, in which both before and after fungal infection there was no significant difference between monoculture and polyculture yield, productivity, and temporal stability. No differ- ence between treatments is likely due to the species used for the monoculture treatment (S. capricornutum) being both competitively dominant and least susceptible to infection causing the polyculture treatment to rapidly become entirely composed of S. capricornutum (Section Fungal infection). Physical and chemical conditions of raceways Over the 43-day course of the experiment, the mean physical and chemical conditions of the replicate ponds were comparable between treatments (Control-monoculture vs. Impact- Fig 2. Mean production metrics of algal cultures before and after infection. Mean values for productivity (A),

stability (B), and maximum biomass achieved immediately prior to harvest (C). Central data points with error bars show the grand mean of all replicates for each treatment with standard error bars. Offset data points represent the mean values for each replicate pond. https://doi.org/10.1371/journal.pone.0267674.g002 PLOS ONE Biodiversity, biofuel and disease: Ecological engineering in algal feedstocks PLOS ONE | https://doi.org/10.1371/journal.pone.0267674 April 28, 2022 8 / 15