Comparative analysis of photosynthesis of three Stipa species based on a photosynthesis model

We compared photosynthetic characteristics of three Stipa species in NECT, Stipa baicalensis, S. grandis and S. breviflora based on ecophysiological traits derived from parameters of a photosynthesis model. Diurnal net photosynthesis rates, transpiration rate and stomatal conductance, together with microclimate variables of the respective species and sites were observed in July 2004. Net photosynthesis rates of three Stipa species were then regressed on incident light intensity, leaf temperature and CO₂ partial pressure, and stomatal conductance by means of the nonlinear least square technique and the modified Thornley and Johson´s leaf photosynthesis models. The results showed that Thornley and Johson´s photosynthesis model explained on 60.49%, 86.17% and 81.36% of variations in observed net photosynthesis rates for three S. baicalensis, S. grandis and S. breviflora, respectively. The difference in photosynthetic characteristics for three Stipa species explained adaptation to conditions of their respective sites. High photo efficiency of S. baicalensis is an adaption to lower photosynthetic active radiation (PAR) at high latitude of the meadow steppe site. On the other hand, S. grandis in typical steppe and S. breviflora in desert steppe sites are located at lower latitude with more available PAR, thus they showed relative lower photon efficiency. Carboxylation conductance of S. baicalensis is low because of their low leaf nitrogen concentration, which may be caused by the low available soil nitrogen due to low decomposition rates at high latitude. In contrast to S. baicalensis, S. breviflora shows much lower base rate of mitochondria respiration because of higher leaf temperature often experienced by plants at desert steppes.