Plants experience stress competing for water with neighboring plants, both with members of the same species (intraspecific competition) and different species (interspecific competition). As plants conduct photosynthesis, they open pores in their leaves called stomata to uptake carbon dioxide from the atmosphere. However, there is a tradeoff: as carbon is gained, water is lost through evaporation as stomata open during the transpiration process. This tradeoff—the carbon gain to water lost during photosynthesis—represents the plant’s water use efficiency. Plant physiological stress due to external factors may affect stomatal regulation and water use efficiency. Through two experiments, one in a controlled growth chamber and the other in the natural area of Red Butte Garden, this study analyzes the differences in water use efficiency of native Utah plant species (Populus tremuloides, Quercus gambelii, Acer grandidentatum and Acer negundo) as they face differing levels of interspecific and intraspecific competition. We found that generally, plants facing higher levels competition exhibit lower water use efficiency. Understanding the correlation between competition and water use efficiency will help predict future plant and forest success not only to stressors such as competition, but also to changing water availability resulting from global climate change.

The datasets contained here are as follows: calculated water use efficiency (WUE) and competition indices (CI) for individual trees in Red Butte Garden interspecific experiment: Quercus gambelii, Acer grandidentatum and Acer negundo (using Hegyi’s 1974 equation for competition index), and the transpiration (E), photosynthesis (A) and stomatal conductance (gs) for each tree. There were two dates of data collection: June 28, 2016 and July 3, 2016. These same gas exchange variables were recorded for the intraspecific competition experiment, using data from the Anderegg Lab's drought experiment of Populus tremuloides in Fall of 2016. P. tremuloides were either planted one to a pot, or two, to mimic an environment with no intraspecific competition or with intraspecific competition.

Competition indices were calculated using measurements of DBH (diameter at breast height) of 3 experimental trees for each named species in the interspecific competition experiment, and compared to distance from surrounding trees in a 7.0 m radius. Gas exchange variables were obtained from output from a LiCor 6800. Water use efficiency of each tree was calculated with the equation WUE=A/gsw.