Study On Mechanism Of Photosynthesis And Respiration Of Larix Gmelinii Plantations

By using the combination of traditional and modern experimental methods, photosynthesis and respiration of two larch plantations of different age was studied and the results showed as follows.Diurnal changes pf photosynthesis of Larix gmelinii of two larch plantations in May and larch plantation of 31 years old in July are double peak curves; and diurnal change pf photosynthesis of Larix gmelinii of two larch plantations in June and in August and larch plantation of 17 years old in July are single peak curves. Mean values of diurnal photosynthetic rate of Larix gmelinii of larch plantation of 31 years old are greater than those of 17 years old. Diurnal changes of stomatal conductivity are positively correlated with photosynthetic rate while diurnal changes of intercellular CO2 concentration are negatively correlated with photosynthetic rate.Mean values of maximum net photosynthetic rate of Larix gmelinii are the highest. Mean values of maximum net photosynthetic rate of Larix gmelinii and main broad-leaved trees of 31 year-old plantation are greater than those of 17 year-old plantation. The light saturation point Larix gmelinii is the highest in both larch plantations and so is the light compensation point. Mean values of light saturation point of Larix gmelinii and main broad-leaved trees of 31 year-old plantation are higher than those of 17 year-old. Mean values of light compensation point of Larix gmelinii and main broad-leaved trees of 31 year-old plantation are lower than those of 17 year-old. Mean values of apparent maximum quantum efficiency of trees in 31 year-old plantation are greater than those of 17 year-old plantation.Diurnal assimilation amount of Larix gmelinii of 31 year-old plantation in different months are almost greater than that of 17 year-old plantation. Annual assimilation amount of Larix gmelinii of 31 year-old plantation and 17 year-old plantation on unit land is 817.41 and 438.20 g C m-2 respectively.Mean values of chlorophyll content of Larix gmelinii and main broad-leaved trees of 31 year-old plantation are higher than those of 17 year-old plantation. Total chlorophyll content of main broad-leaved trees are higher than that of Larix gmelinii. SPAD values of main broad-leaved trees of 31 year-old plantation are higher than those of 17 year-old plantation. There is good correlation between chlorophyll content and SPAD values.Total carbon content of leaves of Larix gmelinii is the highest in both plantations. Total carbon content of leaves of 31 year-old plantation are almost higher than that of 17 year-old plantation. Total nitrogen content of leaves of 31 year-old plantation are all higher than that of 17 year-old plantation.Soil respiration rate of 31 year-old plantation is higher than that of 17 year-old plantation. However, both root respiration rate and percentage of root respiration to soil respiration of 17 year-old plantation are higher than those of 31 year-old plantation. There is good linear correlation between soil and root respiration and root biomass. Correlation coefficient of root respiration and root biomass is greater than that of soil respiration and root biomass. There is good exponential correlation between soil and root respiration and soil temperature. When soil temperature are higher, increase of soil moisture can promote root and soil respiration. Q10 values for soil respiration are high, indicating the significance of root respiration. Q10 values for root respirationare higher than those for soil respiration. Q10 values of both root and soil respiration of 31 year-old plantation are a little higher than those of 17 year-old plantation. Soil respiration rate of both plantations declines sharply with increase of soil depth. At 30cm deep, microbial respiration is main soil respiration. Annual soil respiration of 31 year-old plantation and 17 year-old plantation are 382.41 and 315.53 g C m-2 respectively and annual root respiration of 31 year-old plantation and 17 year-old plantation are 72.06 and 185.35 g C m-2 respectively.Stem respiration ra...