ObjectiveTo compare the differences of photosynthetic and physiological parameters among crown layers and orientations, and then study the effects of crown layers and orientations on photosynthetic characteristics in Larix kaempferi, and to provide a sound theoretical foundation for developing canopy productivity model and accurately evaluating canopy productivity.

Method7-year-old and 19-year-old Larix kaempferi were selected for researching gas exchange. The canopies of Larix kaempferi were divided into 3 layers equally and each layer was divided further into 4 orientations-east, west, south and north. The photosynthetic and physiological parameters, including light response curve, CO₂ response curve and photosynthetic pigment content, were measured on the needles in different canopy layers and orientations. Then the data were analyzed according to crownlayer.

ResultsVertically, all photosynthetic parameters showed significant differences among canopies except apparent quantum yield in the sampled trees. The maximum net photosynthetic rate, light saturation point, light compensation point and dark respiration rate increased with raising crown in both stand ages of L. kaempferi. The maximum carboxylation rate, maximum electron transport rate, triose phosphate utilization and carboxylation efficiency in lower crown were lowest in all measured trees, while the maximum values of CO₂ compensation point existed in lower crown. There were significant differences exist in all photosynthetic pigments of different canopies in the selected trees. The Chla, Chlb and Car increased with declining crown in both stand ages. Horizontally, Orientation had no significant effect on photosynthetic and physiological parameters for the sampled trees. The mean values of photosynthetic parameters in the south and east represented photosynthetic characteristics of the whole crown of 7-and 19-year-old trees, respectively. There were no significant differences in photosynthetic and physiological parameters between 7-year-old and 19-year-old L. kaempferi.

ConclusionThere are considerable spatial heterogeneity of photosynthetic and physiological parameters in L. kaempferi crown, and most of these parameters are affected significantly by crown layer, but not by orientation.