| Pinus taeda is the most important industry tree species in southern America. It has been introduced to China since 1948, and becomes one of the major tree species of plantations in middle and north subtropic in China. Based on the investigation of experimental plantations of Pinus taeda located in the middle region of Anhui province, the ecophysiological characteristics of Pinus taeda and its plantations were studied in this paper, which include photosynthesis, stem sap flow, nutrient contents, nutrient cycling and the character of water and soil erosion in the young plantations. Furthermore, the optimum stand structure of Pinus taeda including planting density, distribution of the planting spot, thinning, choice and distribution of mixed tree species, were also studied. On the bases of the result obtained from this research, a comprehensive and ecological management techniques of Pinus taeda plantation was suggested in order to achieve sustainable management of the plantation. The key results are as follows:1. Photosynthesis ecophysiology of Pinus taedaPhotosynthesis (Pn, i mol CO2 m-2 s-1), transpiration (Tr, m mol m-2 s-1) and some ecophysiological factors such as stomata conduction (COND, mol m-2 s-1),dense of CO2 between cells(Ci, u mol CO2 mol-1), dispatch of saturation air press( VPD, Kpa), air temperature( Ta, ), leaf temperature( Tl, 癈 ), available radiation of photosynthesis( PAR, i mol photons s m-2s-1), relative humidity of air (RHr,%),relative humidity of leaf chamber(RHs,%),enter dense of CO2 (Ca, V mol CO2 mol-1), dense of CO2 in leaf chamber( Cs, i mol CO2 -mol-1) of different management Pinus taeda stands were investigated using the portable photosynthesis system Licor-6400. The results as follows:The daily course of net photosynthesis velocity of Pinus taeda is a single width curve. Before 10 A.M., it is ascend rapidly, and the peak appears between 12 and 14 hours of the day. After 2 p.m., it is descend quickly.When doubled the dense of CO2, the difference of net photosynthesis velocity of Pinus taeda is significant. As the dense of CO2 is 800 i mol CO2 mol-1 and 400 i mol CO2 Mol-1, net photosynthesis velocity is 4.10 and 2.25 i mol CO2 m-2 s-1 respectively. Doubled the dense of CO2 could increase photosynthesis velocity greatly.To the stands of Pinus taeda with different thinning intensities, the net photosynthesis velocity shows remarkable difference, of which the average of strong thinning 3.57 i mol CO2 m-2 s-1, the middling thin is 3.01 u mol CO2 m-2 s-1 the weak thin is 3.10 u mol CO2 m-2 s-1To the stands of Pinus taeda with different densities, velocities of net photosynthesis show remarkable difference, of which the average of 1667 stems / ha stands is 4.26 u mol CO2 m-2 s-1, 1111 stems/ ha is 3.98 u mol CO2 m-2 s-1, 3333 stems/ ha is 3.95 u mol CO2 m-2 s-1The average velocities of net photosynthesis show significant difference in different types of needles. They are 3.15 and 3.21 i mol CO2 m-2 s-1 in upper and central needles respectively and 3.39 and 2.89 i mol CO2 m-2 s-1 in one year and two years needles respectively.In different thinned Pinus taeda stands, the velocities of transpiration show notable difference. To the strong thinned stand, the average is 0.708 m mol m-2 s-1 while to the weak thinned, the average is0.581m mol m-2 s-1 and to the middle, which is 0.518 m m-2 s-1The velocity of net photosynthesis of Pinus elliottii stands with 1111 stems/ ha is 4.91 u mol CO2 m-2 s-1, which is much greater than Pinus taeda stands.Regression analysis shows that there exists good relationship between the velocity of the net photosynthesis and the physiology ecosystem factors, and the relation coefficient (R) reached 0.9977, and decision coefficient (RR) is 0.9954. The all path analysis shows that the direct function (arithmetic figure in the brackets is direct function coefficient) of each factor is in proper order for: Ca(10.730)> Cs(-10.287)> RHs(-0.464)> RHr(0.405)> COND(0.320)> Tl(-0.259)> Tr(0.235)> VPD(0.098)> Ci(-0.085)> Ta(0.051)> PAR (0.038). Except Ca... |
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