LB 9-92 - Climate change and plant-microbe interactions: water-availability influences the direction and specificity of microbial effects on plants

Background/Question/Methods:

Soil microbes are a key structuring force behind plant community structure and composition. How soil microbes affect plants often depends on the abiotic-context of their interactions. Therefore, climate change may alter plant communities through changes in plant-microbe interactions. Importantly, if climate change causes a change in plant-microbe interactions that affects all species equally, no resulting change in plant community structure is expected. To alter plant community structure, climate change must cause plant-microbe interactions to differentially affect species. Expecting an increase in drought and flooding events associated with climate change, if we understand how water availability influences soil microbes and their effects on plants, we will be better able to forecast climate-mediated alterations to plant-microbe interactions and the following consequences for plant community dynamics. We grew paired congeners of 3 native coastal prairie plant species (Bothriochloa barbinodis, Paspalum floridanum, Verbena xutha) and 3 invasive plant species (Bothriochloa ischaemum, Paspalum urvillei, Verbena brasiliensis) with or without the presence of a pathogenic soil fungi (Fusarium incarnatum-equiseti species complex 6b) under drought, average rainfall, and flooding conditions. Watering treatments were imposed for 7 weeks after which the aboveground and belowground plant biomass was harvested, dried, and weighed.

Results/Conclusions:

We tested treatment effects on total plant biomass by fitting generalized linear models with the fixed effects of plant species, watering availability, presence of Fusarium, and all possible interactions followed by a three-way ANOVA. The model revealed significant microbial effects by host species identity (F5, 324 = 5.89, P < 0.0001) whereby plant species responded differentially to Fusarium. Additionally, plant genus was a stronger predictor of plant response versus native-invasive status, suggesting genetic similarities are more important in host-Fusarium associations over indigenous pathogen susceptibility or resistance. Most notably, there were significant interactions between the presence of Fusarium, host species identity, and water availability (F10, 324 = 2.93, P < 0.002) where the effect of Fusarium became more antagonistic and species-specific at high water availability and less so at low water availability. Therefore, it may be expected that stronger and more species-specific microbe effects could drive changes in plant community composition in wetter conditions, but plant-microbe interactions may be less important for plant community structure in drier conditions. Our results highlight the plasticity of plant-microbe interactions and the importance of untangling specific soil microbial responses to altered abiotic conditions to inform our predictions and mitigation strategies for environmental change.