Climate change, land-use changes and overexploitation of natural resources have resulted in the 6th mass extinction imperiling ecosystem functions and services worldwide. Experiments simulating such species loss from grassland ecosystems have illuminated many processes underlying the often-observed detrimental effect of biodiversity loss on ecosystem functioning and stability. However, plant evolutionary processes have been largely overlooked despite their potential allowing ecosystems to regain functioning and stability over time, even when staying at low diversity. We explored such evolutionary adjustments in a long-term grassland biodiversity experiment, the Jena Experiment. We established an elaborate and complex experiment, in which we grew nearly 100 plant communities with a history of co-occurrence (selected communities) next to the same communities of plants with no such history (naïve communities) over four years in the field. In addition, we manipulated the soil in which they were growing, either adding co-evolved microbial communities or removing them. To test the influence of evolution, we measured plant biomass as proxy for ecosystem functioning over several years. In addition, we genetically analyzed plant populations with a history in mixture vs. monoculture to assess whether adaptation to the community context could improve community performance.
Results/Conclusions
We found strong effects of natural selection in the field on both community performance and stability. At low diversity, the co-occurrence history increased community productivity, conceivably via (diffuse) co-evolution among the species growing together in a specific community. Further, less diverse communities among selected communities had temporally more stable biomass than the same naïve communities and showed greater biomass recovery following a major flood, resulting in more stable post-flood biomass. We observed significant divergence in genetic and DNA methylation patterns according to selection history (mixture vs. monoculture) in three perennial grassland species with DNA methylation differences mostly reflecting the genetic differences, suggesting that the observed effects of evolution have a genetic basis. These results were consistent across soil treatments simulating the presence or absence of co-selected microbial communities.
We suggest that plant evolution in a community context can in part compensate for species loss as can high plant diversity in part compensate for the missing opportunity of evolutionary adjustments. We argue that to enhance our understanding of ecological and evolutionary processes in communities, large, multi-factor, multi-year experiments mirroring natural complexity as much as possible are needed to complement synthesis approaches with large observational datasets.