COMPARATIVE STUDIES OF PHOTOSYNTHETIC CHARACTERISTICS IN TYPICAL ALPINE PLANTS OF THE QINGHAI-TIBET PLATEAU
青藏高原几种典型高山植物的光合特性比较

The photosynthetic characteristics of three medicinal alpine plants, Rheum tanguticum, Anisodus tanguticus and Gentiana straminea, were studied and compared to a low land species, Isatis indigotica. The response of net photosynthesis rate (P-n) to intercellular CO-2 concentrations (C-i) and photon flux density (PFD) was determined using a LI-6400 photosynthesis system. The photosynthetic pigments and UV-B-absorbing compounds also were determined in the four species in order to evaluate differences in their photosynthetic characteristics. The results indicated that the three alpine plants had relatively low photosynthetic quantum yields (AQY) as compared to the low land species of I. indigotica, and AQY, carboxylation efficiency (CE) and photorespiratory rate (R-p) were the lowest in R. tanguticum. However, P-n did not respond strongly to changes in PFD, which may be due to the high concentration of photosynthetic pigments and UV-B-absorbing compounds in the leaves. Similar to R. tanguticum, the alpine plant G. straminea also had higher contents of UV-B-absorbing compounds, chlorophyll and carotenoids, but its R-p was higher and P-n was limited by stomatal conductance in response to PFD and P-n was lower. The photosynthetic characteristics of the alpine species, A. tanguticus, was similar to the low land species, I. indigotica, both of which had a high AQY and CE. These results indicated that although there were some differences among the three alpine species, no corresponding characteristics appeared in photosynthetic advancements. The response of P-n to C-i exhibited Pi regeneration limitations after reaching full CO-2 saturation. The changes of R-p in the four species were similar to that of maximum P-n in photosynthetic C-i response.