Climate changes, including chronic changes in precipitation amounts, will influence plant physiology, biomass and productivity, and soil respiration. However, such precipitation effects on switchgrass, a major bioenergy crop, have not been well investigated. Two precipitation experiments (one mesocosm in a greenhouse and one field manipulation) were conducted in Nashville, TN. Both experiments included five precipitation treatments (ambient precipitation, -33%, +33%, -50%, and +50% of ambient). The growing season progression of leaf physiology, aboveground biomass, and soil respiration were determined over two years for each experiment.
Precipitation treatments significantly affected leaf physiology, growth, and aboveground biomass, and soil respiration in both experiments. In the mesocosm experiment, the photosynthetic rates of switchgrass were increased in the wet (+50% and +33%) treatments, but were not changed in the dry treatments, compared to the control. Both aboveground productivity and soil respiration linearly increased with increases in precipitation. In the field experiment, aboveground productivity showed a nonlinear and asymmetric response to precipitation change. Soil respiration had a nonlinear yet symmetric response to precipitation change. This study demonstrated that while switchgrass is a drought tolerant grass, severe drought significantly reduces its growth and biomass, and that high precipitation stimulates switchgrass photosynthesis and growth.