Abstract: [Objective] [Objective]To better understand the spatial heterogeneity of photosynthetic characteristics in canopy of Larix kaempferi, photosynthetic parameters of needles were measured in different canopy layers. This study could provide a sound theoretical foundation for developing a canopy productivity model and accurately evaluating canopy productivity.[Method] The 8-year-old L. kaempferi was selected as the research material, and the canopy was divided equally into 8 canopy layers according to the canopy length from top to bottom. In each tree, only one south-oriented branch was selected in each layer, and the diurnal change of photosynthesis of needles was measured on each selected branch.[Result] The diurnal change of photosynthetic parameters in most canopy layers was similar. Net photosynthetic rate (P_n), transpiration rate (Tr), value of stomatal limitation (L_s), photosynthetically active radiation (PAR), air temperature (T_a) and vapor pressure deficit (VPD) showed a single peak curve, and the stomatal conductance (G_s) gradually decreased from morning. With the increase of canopy, photosynthetic parameters increased, and specific leaf area reduced, while T_a and VPD increased firstly, and then decreased from high to low position of the canopies. There were significant significant differences (P<0.05) in the photosynthetic parameters and the micro-environmental factors among different canopy layers. The P_n, PAR, G_s, and (Tr) had exponential function relationships with relative canopy height (R² ≥ 0.94), and the T_a and VPD had quadratic function relationships with relative canopy height (R² ≥ 0.79). The result of path analysis showed that PAR was a main factor influencing P_n, but the impact of T_a and air humidity was relatively limited.[Conclusion] Photosynthetic effective radiation and photosynthetic activity of mesophyll cells were the main environmental and physiological factors affecting the spatial variation of P_n in L. kaempferi canopy. P_n increased significantly with the increasing canopy, while P_n at the bottom of L. kaempferi canopy was negative, indicating that the part of canopy remained in the state of carbon consumption. Therefore, we suggest that the results can be used as the important indicator for artificial pruning of L. kaempferi larch, and also can be used as the important theoretical basis for developing canopy productivity model and estimating canopy productivity.

Key words: Larix kaempferi, photosynthetic characteristics, canopy, spatial variation, path analysis