CANCELLED - Love thy neighbor? Understanding the effect of elevated carbon dioxide and drought in the interaction between two grasses.

Background/Question/Methods

Projected increases in atmospheric CO2 concentration and drought events are likely to affect the productivity of plants and alter interactions between them. Depending on the combined environmental effect, the interactions between plants can be positive (competition) or negative (facilitation). To understand how elevated CO2 and drought affect the plant-plant interaction between two codominant grasses, Andropogon gerardii and Sorghastrum nutans, we set up a mesocosm experiment in open-top CO2 chambers at Smithsonian Environmental Research Center, Edgewater, MD from June to August 2021. We expected that drought would decrease grasses productivity and there will be competition between them. Further, we hypothesized that when grasses were subjected to elevated CO2 and drought, elevated CO2 would alleviate drought stress in both grasses and result in facilitation between them. Our plant treatments were: (i) One A. gerardii (ii) One S. nutans (ii) Two A. gerardii (iv) Two S. nutans (v) One A. gerardii and one S. nutans. Four treatments for CO2 and water were: (i) Ambient CO2 and ambient rainfall (ii) Ambient CO2 and drought stress (iii) elevated CO2 (1000 ppm) and ambient rainfall (iv) elevated CO2 (1000 ppm) and drought stress.

Results/Conclusions

Elevated CO2 interacted with drought treatment (p< 0.0001) across plants treatment for both grasses and alleviated drought stress as was expected. Drought treatment with ambient CO2 increased competition among plants growing with the neighbor of same species and for plants growing with the neighbor of different species (p< 0.001). We did not find any evidence of facilitation as we had expected for plants under elevated CO2 and drought. Overall, our study suggests that environmental factors could alter plant-plant interaction.