2018 ESA Annual Meeting (August 5 -- 10)

PS 33-125 - Exploring the role of plastic responses in competitive intensity and coexistence

Wednesday, August 8, 2018
ESA Exhibit Hall, New Orleans Ernest N. Morial Convention Center
Alicia J. Foxx, Plant Science and Conservation, Chicago Botanic Garden, Glencoe, IL, Brooke Allen, North Central College and Andrea T. Kramer, Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL
Background/Question/Methods Plastic responses are beneficial to plants coping with climate change and environmental heterogeneity. The response of plants to stimuli have been well studied, however, understanding the impact that plastic responses have on plant-plant interactions remains understudied. Competition plays a large role in community assembly and coexistence dynamics. The modern coexistence theory (Chesson 2000) is anchored in competition; it emphasizes that conspecifics compete more intensely (stabilizing mechanisms) and that competitive differences be equal (equalizing mechanisms) for species to coexist. Plastic responses can alter the outcome of competition and thus the outcome of both stabilizing and equalizing mechanisms. The effects of plastic responses on competition of a native western US grass (Pascopyrum smithii) and the invasive, Bromus tectorum, are studied here. I ask whether there are differences in morphological and soil properties of the focal species as a result of competition with intraspecific and invasive interspecific plants? And whether individuals with induced plastic responses from previous competition will cause changes in competitive intensity with intraspecific plants. In a two-part greenhouse experiment, plastic responses were induced in P. smithii using competition from conspecifics and the invasive grass. Plants were either harvested for above- and belowground trait quantification, or a subset were transplanted to pots with new, same-aged conspecific competitors. Soil organic matter content was recorded for all treatments in the first experiment to quantify if rhizospheric organic matter was related to competitive intensity. Following an additional four weeks, plants were harvested for trait quantification and appraisal of competitive intensity.

Results/Conclusions In the first experiment and following contrasts of means, I found that P. smithii’s root investment (root mass fraction - RMF) when grown with the invasive differed from its growth with conspecifics (p < 0.0001, r2 = 0.51), and that growth with the invasive suppressed root growth. The soil organic matter content did not differ by competition treatment. In the second experiment, I found that P. smithii’s shoot mass following competition with conspecifics differed when the focal plant had been previously induced by the invasive versus conspecifics (p < 0.005, r2 = 0.28). Although the pattern of growth was similar between both experiments. Preliminary results suggest that induced plastic responses do not have dramatic impacts on stabilizing and equalizing mechanisms and thus coexistence. However, further work is needed to assess competitive intensity and its relationship between both experiments to fully address the whether previous competition will cause changes in competitive intensity with intraspecific plants.