[Spatial heterogeneity of canopy photosynthesis for Larix olgensis.]

Based on a 14-year-old planted Larix olgensis in the Maoershan Forest Farm, Heilongjiang Province in 2014, the spatial heterogeneity of photosynthetic indicators, environmental factors and photosynthetic physiological parameters were analyzed, meanwhile the relationship between net photosynthetic rate (P_n) and other indicators were studied. Results showed that in the vertical direction, P_n, stomatal conductance (g_s) and transpiration rate (T_r) were higher in upper than middle and lower canopy significantly, intercellular CO₂ concentration (C_i) increased in the sequence of upper < middle < lower canopy. Photosynthetic active radiation (PAR) decreased from outside of upper to inside of lower canopy significantly, vapor pressure deficit (VPD) and needle leaf temperature (T_l) in upper canopy were respectively higher than in middle and lower canopy significantly, while relative humidity (RH) showed no significant difference with spatial location. The mean value of maximum P_n(P_{n max}), dark respiration rate (R_d), light compensation point (LCP) and light sa-turation point (LSP) followed the pattern of upper > middle > lower canopy and decreased by 32.7%, 55.8%, 80.2% and 51.6% from upper to lower canopy respectively. Apparent quantum yield (AQY) in lower canopy was 1.2 and 1.3 times as much as that of middle and upper canopy, respectively. In the horizontal direction, P_n, g_s, T_r, PAR and VPD were significantly higher from outside to inside in the upper crown, but C_i and RH showed no significant diffe-rence. The mean value of P_{n max}, R_d, LCP and LSP declined by 0.4%, 37.7%, 42.0% and 16.4% from outside to inside, on the contrary, AQY was 0.7% higher from inside to outside. C_i was the main physiological impact factor for P_n, and PAR was an important environmental factor that had the most obvious influence on P_n, especially in weak light region. Therefore, spatial heterogeneity should be considered necessarily when simulating and/or predicting the tree canopy photosynthesis.