Effects of precipitation change on switchgrass gas exchanges and biomass
As global warming continues, it is predicted that more extreme precipitation events will occur in the future. However, how the precipitation change would influence switchgrass physiology and biomass has not been well investigated. We conducted a precipitation experiment with large pots and automatic irrigation systems in an environmental controlled greenhouse in Nashville, TN. A randomized complete block design was used. Five precipitation levels were set including ambient precipitation year (a typical year as the mean precipitation of 30 years) +33%, +50% of ambient to simulate wet years, and -33% and -50% of ambient to simulate dry years. Each treatment was replicated five times. Two-year old plants of switchgrass were transplanted to the pots (25 gallons each) in May 2013, and the precipitation treatments were applied in Feb 2014. Leaf physiology were measured bi-monthly, and above-ground biomass were harvested and measured twice a year.
Preliminary results indicated that no significant differences in plant physiology were observed before the precipitation treatment. In the growing season of 2014, the photosynthetic rates in the +33% and +50% treatments were about 18.8 µmol CO2 m-2s-1, significantly higher than other three treatments. The lowest one was found in the -50% treatment (16.3 µmol CO2 m-2s-1). Seasonal variation of leaf photosynthesis was observed, with the maximum value appeared in May. The biomass in the +33% treatment was the highest and the lowest was observed in the -33% treatment. This study indicates that although switchgrass is a drought tolerant grass, high precipitation stimulates switchgrass photosynthesis and growth.