Abstract: In order to reveal the photosynthetic characteristic variations of different provenances and provide the theoretical basis for the work of provenance selection, the seedlings of Chinese pine (Pinus tabulaeformis Carr.) from five provenances, including provenances Luonan (LN) and Huangling (HL) from Shaanxi, Lvliang Mountain (LL) and Lingkong Mountain (LK) from Shanxi and Qian Mountain (QM) from Liaoning were planted in Loess Plateau. The photosynthetic parameters and their correlations to environmental factors were studied with Li-6400 portable photosynthesis system under natural condition in order to reveal the mechanism of adaptation of different provenances. The results indicted that the diurnal dynamics of net photosynthetic rate (P_n), transpiration rate (T_r) and stomatal conductance(G_s) for five provenances were double-peak curves with obviously midday depression in P_n. The water use efficiency (WUE) of porvenance QM had only one peak, while those of provenances LN, LL, LK and HL had two peaks. The first peaks for all provenances occurred at 8:00 or 10:00, and the second peaks of provenances LN, LL, LK and HL occurred between 12:00 and 16:00. Based on the tendency of changes in P_n, G_s, intercellular CO₂ concentration (C_i) and stomatal limitation (L_s), we speculate that the midday depressions of provenance HL was not controlled by stomatal factors, while those of the other four provenances were. The daily mean values of P_n, T_r and WUE for provenance LK was the highest and those for provenance HL was lower than the other provenances. The correlation analyses showed that the main factors affecting P_n were air temperature (T_a) and vapour pressure deficit (VPD). The main factor affecting T_r was relative humidity (RH) for provenances LN, LL and LK, while for provenances HL and QM, the main factors were T_a and VPD.

Key words: net photosynthetic rate, transpiration rate, water use efficiency, provenance of Pinus tabuleformis