The role of water availability in diversity-productivity relationships
Soil fungi may play a role in the diversity-productivity relationship through their impact on plant water relations (Lehto & Zwiazek 2011). In the null models, water availability had no significant, direct effect on above-ground productivity, whereas in the models that included fungal richness and community composition, water availability had a positive, direct effect on productivity. Furthermore, fungal richness and fungal community composition mediated negative, indirect effects of water availability on productivity. These negative, indirect effects were strong enough to counteract the positive, direct effects of water availability on productivity, resulting in the apparent lack of a significant, direct effect of water availability in the null models. These results suggest that changes in the fungal richness and community composition under water-limited conditions may alleviate plant water stress and regulate productivity (Gehring et al. 2017).
On the other hand, there was no connection between water availability and diversity effects in the full or null models. Although water availability directly influenced fungal community composition, NE and CE were independent of water availability. This suggests that fungal communities affect tree water relations similarly in monocultures and mixed communities. Therefore, the mechanism of complementarity in this system is likely not related to buffering of water stress in mixed communities (Verheyen et al.2008; Belluau et al. 2021). Instead, we suggest that fungal communities may play a role in diversity-productivity relationships and complementarity through the interaction of pathogens and ECM, which may be associated with biotic feedbacks and/or niche partitioning.