Abstract: Diurnal changes of net photosynthetic rate (P_n)of Bauhinia championii on Guilin's Karst hills were measured by Li-6400 portable photosynthesis analysis system (LI-6400,Li-cor USA) in different seasons.Itwas found that diurnal curves of P_n were “single peak” in spring and winter,but “double peak” in summer and autumn and they were both with a significant “midday depression of photosynthesis”.P_n reduction at noon in summer was mainly originated from nonstomatal limitation,while it was mainly due to stomatal limitation in autumn;Bauhinia championii showed higher growth potential in summer and autumn,the seasonal changes of P_n were in the order of summer＞autumn＞spring＞winter;The positive relationship models between P_nand its influence factors were all significant (P＜0.01) in different seasons.Statistical analysis indicated that diurnal changes of P_n were affected by stomatal conductance (G_s) and intercellular CO₂ concentration (C_i) in spring,photosynthetic active radiation (PAR) was the main factor influencing P_n in summer,the dominant factor for P_n in autumn was G_s,and P_n in winter was contributed to the the co-effects of C_i andtranspiration rate (T_r).

Key words: Bauhinia championii, photosynthesis, daily change, seasonal change, influential factors