Abstract:

The basic features of photosynthesis and transpiration of three Chinese Fir (Cunninghamia lanceolata) stands of different density(1 667 tree·hm^-2, 3 233 tree·hm^-2 and 9 767 tree·hm^-2) were measured in the field. The results showed that the light compensation point, the light saturation point and the maximum photosynthetic rate of needles of different positions of crown and different ages were different. In the same layer of the crown, the photosynthetic rate (A) of the mature needles was of the law of the current needles higher than one-year-old needles and one-year-old needles higher than two-year-old needles. In the strong radiation the transpiration rate (E) of the needles at the middle crown layer was less than that of the needles at the upper layer. But in the weak radiation,E of the needles below the middle crown layer was higher than that of the needles at the top layer.Generally, the light saturation point was 1 000～1 900 μmol·m^-2s^-1PAR,but the light compensation point could be low to 4.780～30.114 μmol·m^-2s^-1.the photosynthesis and transpiration capacity of needles in different positions and of different ages in the same branch was different. The photosynthesis and transpiration capacity of the needles in hind part of a branch was less than that of the needles in the front and the middle, but higher utilization rate of quantum or lower light was found for current needles 0.006 60 μmolCO₂·μmol^-1PAR, one-year-old needles 0.017 94 μmolCO₂·μmol^-1PAR and two-year-old needles 0.012 97 μmolCO₂·μmol^-1PAR respectively. The maximum photosynthetic intensity was up to 13.335 μmol CO₂·m^-2s^-1. A/E of the needles in a branch changed in the range of 0.003 5～0.007 gCO₂·g^-1H₂O,and the needles in the hind was of lower A/E. Generally, the photosynthesis capacity of shined needles was 2～4 times of that of shaded needles. A and E of the needles at the top of the branches were stronger than that at both the middle and the hind, and two peaks existed for the daily change of A and E in the growing season for the current needles. It was found that the radiation, the air humidity or the vapor pressure was the key factors to control the stomatal conductance,A and E. The respiration was controlled by the temperature, the humidity of the around air and the boundary layer of the needles. The respiration was higher in day than that at night, and it was in single peak at noon. Good linear relationship was found between the E and respiration. In stands of different density, higher density meant lower average nitrogen content of needles and lower light saturation point and higher light compensation point which led the tree to tend to use the lower light and to be of week growth. In the three stands, for the needles with different ages, the stand of lower density was of higher photosynthetic intensity.

Key words: Cunninghamia lanceolata, Photosynthesis, Transpiration, Respiration