Study On Key Process Of Carbon Cycle In Larix Gemelinii Plantation

In this research, we studied on photosynthesis and soil respiration of Betula platyphylla Suk. leaves and Larix gmelinii (Rupr.) Rupr. needles in Larix gmelinii plantation. The results showed as following:1. Light-response of Birch leaves, larch current-year and previous-year shoot needles were caculated, using 7 light response models. To compare the estimated values of coefficient of dermination, net maximum photosynthesis and dark respiration, we considered that model 5 and model 6 were most suitable to reflect their light-response.2. Gradients change in light intensity resulted in significantly gradients change of net maximum photosynthesis in birch leaves. It indicated that birch leaves quite depended on light intensity. Also, net maximum photosynthesis of birch leaves obviously changed with seasonal variation. Mean value was relatively high in June and July, which was highest in July, and relatively low in August and September. Larch needles were not dependent on light intensity as birch leaves. Net maximum photosynthesis of current-year shoot needles had no significant differences in different canopy positions, while it was significantly higher in upper than that in middle and lower canopy. Net maximum photosynthesis of current-year shoot needles obviously changed with seasonal variation: the value in June and July was almost the same, and it was higher in August and September. Net maximum photosynthesis of previous-year shoot needles kept stable among different canopy positions and months.3. Dark respiration of birch leaves and larch needles had no significantly differences among different canopy positions, but significantly changed with seasonal variation. The change of dark respiration was almost the same with that of leave temperature. However, the correlation between dark respiration of previous-year shoot needles and leave/needle temperature was better than that of current-year shoot needles birch leaves.4. Apparent quantum yield (AQY) of three leave patterns was stable. It didn't significantly change with seasonal variation. AQY of larch needles significantly changed with seasonal variation. AQY of current-year shoot needles was highest in July, while previous-year shoot needles in August. AQY of birch leaves was highest as a whole. Maximum AQY of larch current-year shoot needles was higher than previous-year shoot needles.5. Light compensation point (LCP) of birch leaves and larch needles changed with dark respiration, as LCP is the value when photosynthesis is equal to dark respiration. So the change of LCP resulted from dark respiration. Dark respiration of larch previous-year shoot needles didnn't change with seasonal variation or canopy positions, so the change of its LCP resulted from acclimation to light gradients.6. Light saturation point (LSP) of birch leaves was not affected by seasonal variation, but significantly affected by canopy positions. LSP of larch current-year shoot needles was significantly affected by canopy positions and seasonal variation, while LSP of larch previous-year shoot needles was not affected by them. LSP of three leave patterns changed with their net maximum photosynthesis. So the change of net maximum photosynthesis might result in the change of LSP. LSP of birch leaves was lower than larch needles, while its net maximum photosynthesis was higher than larch needles. This might result from high AQY of birch leaves. It showed that larch needles required more light and was more capable to utilize high light than birch leaves. LSP of different aged shoots also changed significantly. Previou-year shoot needles was significantly higher than current-year shoot. This might relate to needle development.7. Respiration of soil with litter fall was higher than that with no litter fall in the whole growth season. There was no exponential correlation between soil respiration and soil temperature, but linear correlation was more obvious. The correlation of soil with litter fall respiration was better than that with no litter fall. Maximum respiration value of soil with litter fall occurred in August, a bit lower in June and July, lowest in September and October. Respiration of soil with no litter fall didn't change much with seasonal variation. It was higher in July than that in October.In conclusion, trees' photosynthesis and respiration changed with canopy positions and seasonal variation. Seasonal variation of soil respiration also obviously changed. So these factors should be considered when estimating carbon balance of a community.