Study On The Photosynthesis Physio-ecological Characteristics And Sap Flow Of Tectona Grandis In Jianfengling, Hainan Island

This dissertation was funded by the key project (30371182) of the National Nature Science Foundation of China "Study on the data scaling of tropical forestry physiecology"and the key project (2001-08) of Administration of Science and Technology and Administration of Forestry. We systematically measured CO₂ assimilation of teak (Tectona grandis) plantation under natural condition during wet season (July to September) and its responses to variations in light flux density and CO₂ concentration with Li-6400(Li-cor, Inc, USA) in Jianfengling, Hainan Island. In the program, the Thermal Dissipation Method was introduced with the auto data collection instrument ICT-2000TE (Transpiration-Environment). The sap flow density of sample tree measured with the thermal dissipation probe during wet season (July to September) and dry season (March to May), and the relation of sap flow density with environment was summarized and their multiple regression models of different seasons, and different sample tree were established. The main results were given as follows: (1) There is high current biomass of twenty-one years old Tectona grandis plantation in Jianfengling, Hainan Island. The total biomass of tree layer of the plantation was 306.98t·hm^-2, of which the stem accounted for 140.22 t·hm^-2, barks 45.25 t·hm^-2, branches 75.48 t·hm^-2, leaf material 19.89 t·hm^-2 and roots 31.13 t·hm^-2. The underground biomass is about 11.2% of the aboveground biomass. The correlation coefficient squares of stem biomass, bark biomass, root biomass and total biomass with D2H were more than 0.96. As a result, the regression equation, W=a(D2H)b, is fit to each component of the biomass of a stand. (2) Distinguishing light response of photosynthesis in different neighborhood interference. Plants have formed themselves adaptive characteristics of photosynthetic light response in the long-term adaptation to light environments. The range of LCP was 7.30～30.90μmolm-2s-1. The range of dark respiration rate was 0.45～1.63μmolm-2s-1, and the range of apparent maximum photosynthetic rate was 6.39～19.10μmolm-2s-1.Apparent quantum yield changes between 0.0429～0.0533μmolmol-1. An empirical model of photosynthetic light response was constructed by fitting measured data into a non-rectangular hyperbola nonlinear model with the following parameters: the light-saturated photosynthetic rate (Pmax), apparent quantum yield (φ, the initial slope of the curve) and dark respiration rate (Rd). The correlation coefficient squares of empirical model were more than 0.99 under the different CO2 concentration. The results suggest that plant photosynthetic ability can be enhanced as the short-term responses to CO2 enrichment. (3) Distinguishing CO2 response of photosynthesis in different neighborhood interference. The short-term response of photosynthesis in species to enriched CO2 concentration differ from long-term response, but photosynthesis will be increased when CO2 concentration increasing. The response of assimilation (Pn) is modeled as a function of the internal concentration of CO2 in the leaf (Ci). This application fits a model curve described by the rectangular hyperbola: Pn = ηPmaxCi / (ηCi + Pmax) -Rday, where Pn is assimilation, ηis carboxylation efficiency, Ci is internal concentration of CO2 , Pmax is the assimilation at saturating CO2 and Rday is respiratory process(dark). The correlation coefficient squares of empirical model were more than 0.95 in all sample trees. The CO2 compensation point keep rightabout with neighborhood interference. The range of CO2 compensation point was 0.47～65.09μmolmol-1. There was a similar change process of apparent carboxylation efficiency, assimilation at saturating CO2 and dark respiration rate with CO2 compensation point. The range of apparent carboxylation efficiency and assimilation at saturating CO2 were 0.2665～0.8334μmolm-2s-1, 6.65～23.3μmolm-2s-1 respectively. And the range of dark respiration rate was 0.02μmolm-2s-1～5.75μmolm-2s-1. And we study on the photosynthetic under different light density, the result suggest that plant photosynthetic ability can be enhanced as the short-term responses to photons flux density increasing. In Michaelis—Menten models, the correlation coefficient squares were more than 0.87 under the different photons flux density. The results show that apparent carboxylationefficiency and assimilation at saturating CO2 keep same trend with light density, which rang were 0.3108～0.7404μmolm-2s-1 and 7.13～25.90μmolm-2s-1 respectively. (4) Diurnal variations of each tree photosynthetic rate exhibited single-peak or twin-peak. The increasing of internal CO2 concentration in the mid-day showed that the decreasing of net photosynthetic rate was related to non-stomatal restriction factor. The maximum of day average net photosynthetic rate of teak was 14.48μmolm-2s-1, which is higher as much as 154% than minimum of day average net photosynthetic rate. (5) The difference of photosynthesis in species between dry season and wet season are distinguishing not only in individual photosynthetic rate but also in its trend day-timing courses. The net photosynthetic maximum in dry season is higher as much as 36% than that of in wet season. The day average net photosynthetic rate of teak in dry season is 6.36μmolm-2s-1, which is 3.88μmolm-2s-1 in wet season. The net photosynthetic rare in dry season and wet season did not differ from each other (P=0.860). The results showed that apparent carboxylation efficiency and CO2 saturation point in dry season is higher than that of in wet season, but CO2 compensation is higher in wet season. (6) The diurnal course of sap flow density of different neighborhood interference show that there is single-peak in dry season. But maximum values, their corresponding time and day average sap flow density were different from each other. The transpiration flux of 7#, 94# and 96# sample tree are 1.85 kgd-1, 10.07 kgd-1 and 19.64 kgd-1 respectively, which were influenced by sap flow density and sapwood area. The multiple regression models on the responses of the diurnal sap flow density to the related environmental factors (solar radiation, air temperature, air relative humidity, soil temperature, wind speed ) were developed during the dry season, in which the correlation coefficient squares were more than 0.86(P<0.01). As far as sap flow density fit with the model of sample trees in 101d～103d (day of year) were concerned, the trend were similar. The transpiration fluxes of 7#, 94# and 96# sample tree is 5.66kg, 43.74kg and 51.83kg respectively during 101d～103d. (7) The diurnal course of sap flow density of different neighborhood interference show that there is single-peak in wet season. But maximum values, their corresponding time and day average sap flow density were different from each other. The transpiration flux of 94# and 96# sample tree are 11.04kgd-1, 13.25 kgd-1 respectively. The multiple regression models on the responses of the diurnal sap flow density to the related environmental factors (solar radiation, air temperature, air relative humidity, soil temperature, wind speed ) were developed during the dry season, in which the correlation coefficient squares were more than 0.91(P<0.01). As far as sap flow density fit with the model of sample trees in 259d～261d (day of year) were concerned, the trend were similar. The transpiration fluxes of 94# and 96#sample tree is 38.82kg, 31.12kg respectively during 259d～261d.