Photosynthesis, respiration and transpiration are important physiological processes for the survival and growth of green plants. Most of these physiological processes take place over the leaf surface. The leaf area index as the size of the green plant leaf area per unit area is an important indicator reflecting the total area of ​​the photosynthetic, respiratory and transpiration processes of the ecosystem. The leaf area index can be detected using the leaf area detector. The leaf area index has a direct relationship with several important ecological parameters such as ecosystem evapotranspiration, total primary productivity, interception of the canopy light quantity, and so on. Therefore, in some productivity and evaporation The leaf area index in the dispersive model is an important input parameter. Methods for measuring the leaf area index of forests include direct harvesting measurement methods and optical instrumentation measurement methods. The single leaf area of ​​broad-leaved trees is relatively easy to measure either directly or using instruments. There are also many reports related to leaf area index, and coniferous leaves are relatively difficult to measure directly. Therefore, the direct measurement method is applied in the study of early leaf area index. More. With the deepening of research and the appearance of various measuring instruments, there have been reports of the use of instruments (canopy analyzers, etc.) to measure the leaf area index of needles. However, there is a premise that most of the leaf area index is measured by instruments. It is assumed that the leaves are randomly distributed in the canopy space. This condition may only be established when the stand density is high. Moreover, the evergreen conifers have a leaf age of more than 1 year. Due to different leaf ages, there are certain differences in photosynthetic characteristics and specific leaf area. However, instrumental methods cannot distinguish between perennial and current-year leaves. In the report of the direct measurement method used to study the leaf area index of pine plants, most of the conifers are assumed to be cylinders approximately. However, whether they are cylindrical or not is yet to be studied.
Although Pinus elliotii is not a native tree species in China, it is widely introduced in China because of its adaptability, poor tolerance, and ability to produce resins. Pinus elliottii belongs to the evergreen tree species. According to the author's observation, the leaf age is up to 4 years, and there are two types of leaves, one with two needles and one with three needles. This paper proposes to use traditional measurement methods to explore the reliability of calculating the leaf area of ​​each pine wet leaf as a cylinder, study the relationship between the leaf length and leaf area of ​​the wetland pine, and compare the differences in specific leaf area of ​​different types of leaves. Using plot survey data and standard wood data to calculate the leaf area index of Pinus elliottii forest at Qianyanzhou Experimental Station, to provide comparative data for instrumental measurements, and to provide basic parameters for clarifying the productivity characteristics of plantation forests.
1 Sample location The research site is the core experimental zone of the Qianyanzhou Experimental Station of the Chinese Academy of Sciences. It is located in Guanxi Township, Taihe County, Jiangxi Province. According to the recorder, it shows the longitude 115b04c13d and the northern latitude 26b44c48d. The altitude of the test area is about 100m and the relative height is 20~50m. It is a typical red soil hilly landform. The average annual temperature of the experimental area is 1719e, \0e active accumulated temperature is 6523e. The average annual rainfall is 1489mm. The precipitation is concentrated in the 4th to 6th months. In July and August, the temperature is low and the rain is easy to appear. The sunshine duration is 1406h. The annual sunshine percentage is 43%. The annual total solar radiation is 4349MJPm2. The frost-free period is 323d. It has typical subtropical monsoon climate characteristics. The main soil type is red soil. The parent material of the soil is mostly red sandstone, glutenite or mudstone, and river alluvium. The type of land use is mainly planted forest, and the afforestation time is around 1984. The main tree species are Pinus elliotii, P. massoniana and Cunninghamia lanceolata.
2 Research methods Four wetland pines were cut in August 2003. 156 healthy shoots were collected. Perennial and individual leaves of each shoot were collected and weighed. The water content was sampled and converted to dry weight. The percentage of leaves and the current year's leaves, and the establishment of the regression relationship between the base diameter of the shoots and the total leaf biomass, combined with the measurement results of the base diameters of the branches of 15 snow fallen trees to calculate the leaf biomass of these fallen trees, establishing a single wetland pine The functional relationship between the DBH, tree height and leaf biomass. At the same time, sample plots of the wetland pine forest at the test station were surveyed and two 20m@20m plots were made for each wooden inspection scale. In August 2004, a portion of the perennial loose leaf and the current year's leaf were randomly selected and sampled to determine the moisture content. At the same time, two needles and one bunch of perennial leaves, eight leaves of the year, nine leaves of the year, and three bunches of perennial leaves of twelve bunches were taken. Annually 11 leaves, each needle using a 1P100 electronic balance weighing fresh weight and the use of steel tape measure the length of each leaf (l), using digital display vernier caliper (precision 0101mm) to measure the long leaf 1P4, 1P2 and 3P4 The width (d) and the thickness (h) are each three times, and the average value is taken as the width and thickness values ​​at that point, and the average of the three averages is calculated as the width and thickness of the blade. Using a precision chemical instrument such as a burette to measure the volume of each blade according to the principle of drainage, calculate the diameter of each needle as a cylinder and compare it with direct measurement data. In March 2005, 10 trees were surveyed, and the percentage of each year in each branch of each tree was selected to investigate two needles and one leaf and three needles and one leaf. In August 2005, some two-needle bundles and three-needle bundles of blades were taken for freehand slicing. After scanning with a resolution of 1200 dpi, image processing software was used to measure parameters such as blade width, thickness, perimeter, and cross-sectional area to determine the shape of the blade. evidence. The statistical test method used in this paper is based on Tao Xie's 5 applied mathematical statistics method.
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