Climatic warming changes plant photosynthesis and its temperature dependence in a temperate steppe of northern China

Warming responses of photosynthesis and its temperature dependence in two C3 grass (Agropyron cristatum, Stipa krylovii), one C4 grass (Pennisetum centrasiaticum), and two C3 forb (Artemisia capillaris, Potentilla acaulis) species in a temperate steppe of northern China were investigated in a field experiment. Experimental warming with infrared heater significantly increased daily mean assimilation rate (A) in P. centrasiaticum and A. capillaris by 30 and 43%, respectively, but had no effects on other three species. Seasonal mean A was 13, 15, and 19% higher in the warmed than control plants for P. centrasiaticum, A. capillaries, and S. krylovii, respectively. The mean assimilation rate in A. cristatum and P. acaulis was not impacted by experimental warming. All the five species showed photosynthetic acclimation to temperature. The optimum temperature for photosynthesis (Topt) and the assimilation rate at Topt in the five species increased by 0.33–0.78 °C and 4–27%, respectively, under experimental warming. Elevated temperature tended to increase the maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylation (Vcmax) and the RuBP regeneration capacity (Jmax) in the C3 plants and carboxylation efficiency and the CO2-saturated photosynthetic rate in the C4 plant at higher leaf temperature, as well as the optimum temperatures for the four parameters. Our results indicated that photosynthetic responses to warming were species-specific and that most of the species in the temperate steppe of northern China could acclimate to a warmer environment. The changes in the temperature dependence of Vcmax and Jmax, as well as the balance of these two processes altered the temperature dependence of photosynthesis under climatic warming.