Effects of Precipitation Changes on Switchgrass Photosynthesis, Growth, and Biomass: A Mesocosm Study.

Climate changes, including chronic changes in precipitation amounts, will influence plant physiology and growth. However, such precipitation effects on switchgrass, a major bioenergy crop, have not been well investigated. We conducted a two-year precipitation simulation experiment using large pots (95 L) in an environmentally controlled greenhouse in Nashville, TN. Five precipitation treatments (ambient precipitation, and -50%, -33%, +33%, and +50% of ambient) were applied in a randomized complete block design with "Alamo" switchgrass plants one year after established from tillers. The growing season progression of leaf physiology, tiller number, and height and aboveground biomass were determined each growing season. Precipitation treatment significantly affected leaf physiology, growth, and aboveground biomass. The photosynthetic rate in the +50% treatment was 18.7 µmol CO₂ m^-2s^-1, significantly higher than other treatments. The biomass in the +50 % treatment was twice that in the -50% treatment. Compared to the ambient treatment, the -33% treatment did not influence leaf physiology, plant growth, and aboveground biomass, but the -50% treatment significantly reduced plant height and aboveground biomass. This study demonstrated that while switchgrass is a drought tolerant grass, severe drought significantly reduces its growth and biomass, and that high precipitation stimulates photosynthesis and growth.