Developing Temperature-Dependent Functional Algorithms for Switchgrass Growth and Development for Modeling.

Temperature is a primary environmental factor controlling growth and developmental rates of plants, yet little specific information is available regarding switchgrass (Panicum virgatum L.), a warm season C₄ species responses to temperature. An experiment was conducted in sunlit, temperature- and CO₂-controlled plant growth chambers under optimum water and nutrient conditions. Four chambers were maintained at 20/14, 28/20/ 34/26 and 40/32ºC day/night cycles and at 400 ppm of CO2 from 34 to 103 days after sowing (DAS). Prior to temperature treatments, all plants were grown at 28/20ºC. Plant heights and number of leaves were measured weekly throughout the experiment. Leaf area and dry weights were obtained at 21, 42 and 69 days after treatment.  Stem elongation, leaf addition and growth, and biomass accumulation rates were very responsive to temperature.  Major growth rates (stem elongation, leaf area growth, and biomass and photosynthesis) increased linearly with increase in mean temperature up to 29ºC, and the rates remained unaltered/or declined slightly at the highest temperature tested, 34.7ºC. Developmental rates such as leaf addition and tiller numbers increased linearly with increase in temperature. Switchgrass took 80 d to initiate panicles at 29ºC, but required 96 d at 23.7ºC and 87 d at 34.7ºC.  Panicles did not initiate at 18.4 C during this experimental period, 103 DAS. Highest panicle dry weight was observed at 29ºC. Panicle dry weights declined by 72% at 23.7ºC and 35% at 34.7ºC compared to plants grown at 29ºC. Decreased panicle weights at the lower (18.4 ºC) and higher (34.7ºC) temperatures were due to fewer and smaller panicles per plant. The temperature-specific functional relationships for various growth and developmental processes would be useful in predicting and modeling switchgrass in changing environment.