Effect of high temperature on photosynthesis and transpiration of sweet corn (Zea mays L. var. rugosa)

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate (P _N) of sweet corn was found for the lowest temperature of 28-34 μmol m^-2 s^-1 while the P _N for the highest temperature treatment was 50-60 % lower. We detected a gradual decline of about 1 P _N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h^-1 (≈5.0-6.5 mm d^-1) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h^-1 (≈3.5-5.0 mm d^-1) for the low temperature treatment. Cumulative CO₂ fixation of the 40/35 °C treatment was 33.7 g m^-2 d^-1 and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO ₂) kg^-1(H₂O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P _N, and E of Zea: the high temperature which reduced P _N, vapor pressure deficit (VPD) that was directly related to E but did not affect P _N, and quasi stem conductance (QC) that was directly related to P _N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.