Photosynthetic and physiological characteristics of Cladrastis platycarpa（Maxim.） Makino in spring in dolomite rocky hills of karst region

Diumal changes of photosynthesis and light response curve of Cladrastis platycarpa（Maxim.） Makino were measured with LI- 6400xt portable photosynthesis system，and the relationship between photosynthetic physiology and ecological factors were analyzed. The results showed as follows：（1）The diurnal change of net photosynthesis rate（ Pn） of C. platycarpa（Maxim.） Makino had a double-peak curve ，exhibiting a clear midday depress，and the peak value reached at 10：00 and 14：00. Intercellular CO2 concentration（Ci）had opposite diurnal variation compared with Pn. Diurnal variation of transpiration rate（Tr） and stomatal conductance（Cond） had a double-peak curve as Pn. Stomatal limits（Ls）had opposite diurnal variation compared with Ci. The diurnal variation of water use efficiency（ WUE）showed inverse single-peak curve，daily average was 2.91μmol/ mmol.（2）Light saturation point（ LSP） of C. platycarpa（Maxim.） Makino was 984μmol/m2·s，the maximum of net photosynthesis rate（Pnmax）was 18.46μmol/m2·s，dark respiration rate（Rd）was -1.39μmol/m2·s， initial quantum efficiency（α）was 0.0445，light compensation point（ LCP） was 18.37μmol/m2·s.（3）The net photosynthetic rate and environmental factors correlation analysis showed that：Pn was influenced by environmental factors in the order from high to low：Gs>PAR>Tr>Ci>RH>Ca>Ta.