Determination of photosynthetic parameters Vcmax and Jmax for a C3 plant (spring hulless barley) at two altitudes on the Tibetan Plateau

On the Tibetan Plateau, the unique alpine climate factors of low air pressure, low CO2 partial pressure and low air temperature have significant but non-explicit influences on the photosynthetic capacity of plants. To evaluate these influences, we measured the net photosynthetic rates for spring hulless barley leaves at two altitudes of 3688 m (the low altitude) and 4333 m (the high altitude), respectively. Two photosynthetic parameters—Vcmax, the maximum rate of Rubisco carboxylase activity, and Jmax, the maximum rate of photosynthetic electron transport—were determined. The net photosynthetic rate and the photosynthetic parameters Vcmax and Jmax were higher for leaves from plants grown at the high altitude than for those at the low altitude. Vcmax and Jmax were approximately 24% and 22% greater, respectively, for leaves from plants grown at the high altitude. The CO2 and air temperature at the high altitude were lower than those at the low altitude. As a consequence, plants exposed to lower CO2 partial pressure and lower air temperature have a higher photosynthetic capacity on the Tibetan Plateau. The optimal temperatures for Vcmax and Jmax were approximately 6.5% and 3.5% higher, respectively, in leaves from plants grown at the high altitude than those grown at the low altitude, and the ratio of Jmax to Vcmax was 12.7% lower at the low altitude. Simulation analyses revealed that the photosynthetic capacities of plants decreased after long-term increases in CO2 partial pressure and temperature associated with global climate change on the Tibetan Plateau.