To determine the photosynthetic characteristics of C3 plants and their sensitivity to CO2 at different altitudes on the Tibetan Plateau, hulless barley (Hordeum vulgare L. ssp. vulgare) was grown at altitudes of 4,333 m and 3,688 m. Using gas-exchange measurements, photosynthetic parameters were simulated, including the maximum net photosynthesis (Pmax) and the apparent quantum efficiency (α). Plants growing at higher altitude had higher net photosynthetic rates (PN), photosynthesis parameters (Pmax and α) and sensitivities to CO2 enhancement than plants growing at lower altitude on the Tibetan Plateau. The enhancements of PN, Pmax, and α for plants growing at higher altitude, corresponding with 10 μmol(CO2) mol-1 increments, were approximately 0.20∼0.45%, 0.05∼0.20% and 0.12∼0.36% greater, respectively, than for plants growing at lower altitude, respectively, where CO2 levels rose from 10 to 170 μmol(CO2) mol-1. Therefore, on the Tibetan Plateau, the changes in the photosynthetic capacities and the photosynthetic sensitivities to CO2 observed in the C3 plants grown above 3,688 m are likely to increase with altitude despite the decreasing CO2 partial pressure. and Y. Z. Fan ... [et al.].
Gas exchanges and related leaf traits of three co-occurring species of genus Cypripedium (C. yunnanense Franch., C. guttatum SW., and C. flavum P.F. Hunt et Summerch.) were investigated in a scrubland at 3 460 m a.s.l. in the Hengduan Mountains. The considered species had similar photosynthetic responses to photosynthetic photon flux density (PPFD) and air temperature. The photosynthetic capacity (Pmax), carboxylation efficiency (CE), apparent quantum efficiency (AQE), PPFD-saturated rate of electron transport (Jmax), respiration rate (RD), and leaf nitrogen content per unit area (LNC) of C. guttatum were higher than those of C. yunnanense and C. flavum. The highest Pmax of C. guttatum was related to the highest LNC and the lowest ratio of intercellular CO2 concentration to atmospheric CO2 concentration (Ci/Ca). However, no significant differences in stomatal conductance (gs) and relative stomatal limitations (RSL) were observed among the three species. Hence biochemical limitation had a dominant role in
Pmax differences among the considered species. and S. B. Zhang ... [et al.].