Photosynthesis, transpiration, and water use efficiency of Caragana microphylla, C-intermedia, and C-korshinskii

In the order C. microphylla - C. intermedia - C. korshinskii, compensation irradiance, saturation irradiance, and optimum temperature for photosynthesis increased, net photosynthetic rate (P-N) at low irradiance and low temperature decreased, optimum air humidity decreased, and P-N at low air humidity increased. Daily cumulative value of P-N increased while daily cumulative value of transpiration (E) decreased, and hence water use efficiency (WUE = P-N/E) increased. Diurnal course of P-N of C. microphylla was a double-peak curve, but the second peak in the curves of C. intermedia and C. korshinskii was not visible. These physiological characteristics are biological basis for the geographical distribution of these three Caragana species, and are in relation to water conditions of their habitats and distinctiveness in leaf hair of plant.