Research on photosynthesis characteristics of three tree bushes in Beishan Mountain of Lanzhou City

This study mainly measured the diurnal change of photosynthesis characteristics of Tamarix austromongolica, Platycladus orientalis and Caragana korshinskii in the Beishan Mountain of Lanzhou, as well as environmental factors. By using the relational grade analysis of grey system theory, the relational grade between Net photosynthetic rate (Pn),physiological and environmental factors were calculated. The results showed: The diurnal variation of Pn of three species showed asymmetric bimodal peak curve, with a remarkable photosynthetic “midday depressions”. It is caused by the midday high light intensity and temperature, rather than stomatal factors. The relation grades between Pn and physiological factors was Intercellular CO2 concentration (Ci) > Leaf temperature (Tl) > Transpiration rate Tr > Stomatal conductance (Gs) > Saturation vapor pressure difference foliage (VPD) > Stomatal limitating value (Ls) for T. austromongolica, Tr > Tl > VPD > Ci > Ls > Gs for P. orientalis and Tr > Tl > Ci > Gs > VPD > Ls for C. korshinskii. Among them, Ci has a obvious effect on Pn of T. austromongolica and it is Tr for P. orientalis and C. korshinskii. The relation grades between Pn an environmental factors was Photosynthetically active radiation (PAR)> Air relative humidity (RH) > Soil temperature (Ts) > Soil moisture (SM) > Air temperature (Ta) > Atmospheric CO2 concentration (Ca) for T. austromongolica, PAR > SM > Ta > Ts > RH > Ca for P. orientalis and RH > PAR > SM > Ta > Ca > Ts for C. korshinskii. Among them, PAR, has a deeply effect on Pn for P. orientalis and T. austromongolica, while itis RH for C. korshinskii.