We hypothesized that decreased stomatal conductance (gs) at elevated CO2 might decrease transpiration (E), increase leaf water potential (ΨW), and thereby protect net photosynthesis rate (PN) from heat damage in maize (Zea mays L) seedlings. To separate long-term effects of elevated CO2, plants grew at either ambient CO2 or elevated CO2. During high-temperature treatment (HT) at 45°C for 15 min, leaves were exposed either to ambient CO2 (380 μmol mol-1) or to elevated CO2 (560 μmol mol-1). HT reduced PN by 25 to 38% across four CO2 combinations. However, the gs and E did not differ among all CO2 treatments during HT. After returning the leaf temperature to 35°C within 30 min, gs and E were the same or higher than the initial values. Leaf water potential (ΨW) was slightly lower at ambient CO2, but not at elevated CO2. This study highlighted that elevated CO2 failed in protecting PN from 45°C via decreasing gs and ΨW., M. N. Qu, J. A. Bunce, Z. S. Shi., and Obsahuje bibliografii
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 (PN) of sweet corn was found for the lowest temperature of 28-34 µmol m-2 s-1 while the PN 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(CO2) kg-1(H2O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, PN, and E of Zea: the high temperature which reduced PN, vapor pressure deficit (VPD) that was directly related to E but did not affect PN, and quasi stem conductance (QC) that was directly related to PN 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. and J. Ben-Asher, A. Garcia y Garcia, G. Hoogenboom.
Some studies of responses of plants to elevated concentrations of carbon dioxide (EC) added CO2 only in the daytime, while others supplied CO2 continuously. I tested whether these two methods of EC treatments produced differences in the seed yield of soybeans. Tests were conducted for four growing seasons, using open top chambers, with soybeans rooted in the ground in field plots. One third of the chambers were flushed with air at the current ambient [CO2] (AC), one third had [CO2] 350 µmol mol-1 above ambient during the daytime (ECd), while one third had [CO2] 350 µmol mol-1 above ambient for 24 h per day (ECdn). ECdn increased seed yield by an average of 62 % over the four years compared with the AC treatment, while ECd increased seed yield by 34 %. Higher seed yield for ECdn compared with ECd occurred each year. In comparing years, the relative yield disadvantage of ECd decreased with increasing overall seed yield. On days with high water vapor pressure deficits, soybean canopies with ECd had smaller midday extinction coefficients for photosynthetically active radiation than canopies with ECdn, because of a more vertical leaf orientation. Hence the seed yield of soybean at EC varied depending on whether EC was also provided at night, with much greater yield stimulation for ECdn than for ECd in some years.