Lowered precipitation leading to periods of drought associated with climate change may have serious implications for all biota in the southeastern United States. In addition, plants may also have to cope with the spread of invasive species which outcompete native vegetation, particularly individuals that are already under drought stress. The goal of this study was to compare plant functional traits of three pine species (Pinus palustris, Pinus elliottii, and Pinus taeda) under four experimental treatments: control, drought, cogongrass (Imperata cylindrica), and the combined effect of drought and plant invasion. This factorial field experiment allowed us to not only focus on individual stressors, but also their interactions. We measured growth rates, leaf gas exchange rates, leaf nutrients, and photosynthetic water use efficiency (WUE) of seedlings to detect differences in plant stress between treatments.
Results/Conclusions
We found that the drought treatment had the largest negative effect on pine species overall and led to significantly lower seedling growth, a 28.6% decrease in rates of photosynthesis, and a 76.5% increase in rates of WUE. The invasion treatment represented the second largest stressor to the pines, causing similar, but less significant effects on growth and a 21.3% decrease in gas exchange rates of the pines. However, seedlings grown in the drought and invasion combined treatment were less negatively affected than those in the drought only treatment experiencing only a 15% decrease in photosynthetic rates, possibly due to less soil water evaporation. Overall these data improve our knowledge on how these ecologically and economically significant species will react to climate change factors, allowing us to make more informed management decisions.