Aboveground - belowground interactions as a source of complementarity effects in biodiversity experiments

Background/Question/Methods

Current biodiversity research aims at spotlighting the underlying mechanisms of the widely established positive relationship between biodiversity and ecosystem functioning (BDEF). Complementarity between plant species, i.e. complementary nutrient use, facilitative, competitive and antagonistic interactions, has been shown to be more important than selection effects in the long term. Most BDEF studies primarily focused on the interactions between plants. However, plants are embedded in a multitude of multitrophic interactions above and below the ground, which are likely to play a crucial role in BDEF relationships. In the present review I point to the relevance of aboveground – belowground interactions as a source of complementarity effects in grassland biodiversity experiments.

Results/Conclusions

By reviewing current knowledge on the role of soil decomposers, herbivores, arbuscular mycorrhizal fungi, pathogens, predators and biocontrol bacteria in biodiversity experiments I show that soil biota can drive both positive and negative complementarity effects via a multitude of mechanisms. For instance, the action of decomposers and arbuscular mycorrhizal fungi enlarge biotope space for plants, promoting the coexistence and productivity of diverse plant communities. Moreover, one of the most prominent examples of facilitative interactions between plant species, namely the beneficial effect of legumes on nitrogen availability for neighboring non-leguminous plants, is essentially driven by nematodes inducing leakage of nitrogen into the rhizosphere and by decomposers making nitrogen in legume litter available for plants. Further, diverse plant communities have recently been reported to experience less pathogen pressure and have a higher abundance of biocontrol bacteria than low diverse ones. In contrast to these positive feedbacks, plants and soil microorganisms may also compete for nutrients, reinforcing competitive interactions between plants and reducing community productivity.

I conclude that accounting for aboveground – belowground interactions may considerably improve the mechanistic understanding of complementarity effects in plant biodiversity – ecosystem functioning experiments. In analogy to diverse plant assemblages, the recent review paper may stimulate the complementary collaboration between scientists from different disciplines to realistically predict the consequences of biodiversity loss.