Abstract: The photosynthetic characteristics of Caragana davazamcii plants of different ages were investigated. The net Photosynthetic rate(P_n) and transpiration rate(T_r) of mid-aged plants(5 years old) were higher than those of senile plants(24 years old). The decrease of P_n in senile plants between 12:00-14:00 was caused by non-stomatal factors that impaired photosystem Ⅱand photosynthetic capacity of the leaves, while that in mid-aged plants was a consequence of both stomatal and non-stomatal inhibition. The determination of photosynthetic pigment contents showed that the contents of chlorophyll and carotenoid in mid-aged plants were significantly higher than those in senile plants, so that the mid-aged plants had higher P_n, LUE and capcity of intensive radiation adaptation. In addition, the mid-aged plants had higher WUE, which made them more tolerant to drought, so the mid-aged plants were able to adapt to the local envioronments with high temperature and severe drought.

Key words: Age-classes, Caragana davazamcii, photosynthetic physiological characteristics, water utilization efficiency