CANCELLED - Contrasting responses of soil microbes and plant growth to drought and carbon addition

Background/Question/Methods

Increases in drought frequency due to climate change are predicted to reduce crop yields and plant productivity in non-agricultural ecosystems. Microbial communities can alter plant drought response via their relationships with plant roots and can delay soil drying. Therefore, there is opportunity to manage plant drought tolerance through soil microbial communities. However, microbial community response to drought is likely governed by physiological trade-offs between stress tolerance, resource acquisition, and growth efficiency (Y-A-S framework). Therefore, we tested how trade-offs alter microbial activity and plant drought tolerance by first testing a hypothesis of the Y-A-S framework: Increasing carbon resource availability will increase microbial drought tolerance. Then we examined whether the soil microbial activity increased plant drought tolerance. We leveraged a new large-scale rainout shelter experiment at the Kellogg Biological Station LTER. In three field types (convention agriculture, conventional no-till agriculture, and early successional field), we applied two rainfall treatments (drought and irrigated control) and applied two carbon treatments (sorghum addition and control). We measured microbial resource acquisition traits (PCA of five carbon degrading enzyme activities), microbial growth traits (respiration), and plant aboveground biomass. In the future, we plan to add measurements of microbial stress tolerance and growth efficiency traits.

Results/Conclusions

We found that carbon degrading enzyme activity increased in response to carbon addition (F=8.25, p=0.007) across all field types while drought did not alter enzyme activity. Similarly, soil respiration increased in carbon addition treatments (F=4.95, p=0.03) across all field types and drought did not alter soil respiration. While carbon addition increased soil microbial activity and respiration across all field types, carbon addition decreased soybean aboveground biomass in both conventional and no-till conventional field types. Drought also decreased aboveground plant biomass in all field types. Overall, we found no evidence of trade-offs between microbial growth and resource acquisition traits. We also found that the increased soil microbial activity from carbon addition does not translate to greater plant growth.