The Modelling Of Three Dimensional Distribution Of Photosynthetically Active Radiation In Pinus Massoniana Canopy

Photosynethically Available Radiation(PAR,400-700nm) is a part of the solar radiation which can be absorbed by green plants'chloroplast in order to achieve dry matter accumulation. It is one of the basic energy for yield formation, which makes a direct effect on plants growth and its output as well as quality. Pinus massoniana is the main timber tree in south China and the important planting tree for barrel hills in the Yangtze valley. Setting up a model which is appropriate for the three dimensional distribution of Photosynthetically Active Radiation (PAR) in Pinus massoniana canopy has an important meaning on sustainable management of Pinus massoniana plantation and the modeling of photosynthetic and transpiration at canopy level in the future. The research target in this paper was establishing a model of three dimensional distribution of PAR in Pinus massoniana canopy, and introducing the density mechanism, studied the Space-time distribution characteristics of canopy PAR in Pinus massoniana plantation with different density. The main conclusion were as follows:(1) Using the transmittance (Tr%) to analyse the Vertical distribution feature of PAR in Pinus massoniana canopy in different density treatments and the result showed:the average PAR transmittance in different heights and time correlated positively with the solar altitude, and showed a exponential decline trend with the accumulated LAI; the PAR transmittance decreased with the increasing of stand density in the same solar time and heights.(2) Using the transmittance (Tr%) to analyse the horizontal distribution feature of PAR in Pinus massoniana canopy in different density treatments and the result showed: the horizontal distribution was similar in different density treatment, showing a increasing trend from the center to the round of the crown; the horizontal transmittance was relatively high in the north, the radiation intensity distribution in the east-west direct varied with the Solar Azimuth.(3) Using the transmittance (Tr%) to analyse the PAR three dimensional distribution feature of the pinus massoniana canopy in different density treatments and the result showed:the diffuse PAR transmittance was bigger than the total PAR transmittance, but the Variation laws of the two were almost the same both in the vertical and horizontal distribution.(4) Considering the structure character of pinus massoniana and combining the geometrical optics principle and Beer's law, we set up the transmission and distribution model of PAR in the pinus massoniana, which can simulate the PAR of any spot in pinus massoniana canopy at ant solar time.(5) Using the observed values to test the simulation of the model and the result showed:there was a significant linear correlation between the observed values and simulated values of total PAR on the horizontal plane above the pinus massoniana canopy (R2=0.964, P< 0.01),and the simulated values were bigger than the observed values; there was also a good linear correlation between the observed values and simulated values of total PAR in the pinus massoniana canopy (R2=786, P< 0.05), and the observed values were bigger than the simulated values.(6) Simulating the daily course trends of the horizontal average PAR and the east-west section in the pinus massoniana of different density treatments, and the result showd:the observed values was nearly equal to the simulated values.