Simulation And Application Of Canopy Photosynthetic Rate Based On Multilayer Radiative Transfer Model

Phyllostachys pubescens forest has high carbon sequestration capacity,and its carbon sink function has been widely concerned.There are many studies on photosynthetic carbon sequestration capacity at leaf scale and ecosystem scale,but there are few studies on canopy scale between them.The main reason is the difficulty caused by the complexity of canopy structure,as well as the underestimation of the influence on the heterogeneity within the canopy,spectrum and photosynthesis.In this study,the vertical heterogeneity of biochemical and structural parameters in the Phyllostachys edulis canopy was fully considered.The canopy was divided into multi layers from top to bottom to develop a new multi-layer radiative transfer model;The developed multi-layer radiative transfer model was used to simulate the photosynthetically active radiation in the canopy,so that the photosynthetic rate of leaves with different heights in the canopy could be calculated respectively,and the mechanism model of multi-layer photosynthesis simulation was obtained;The multi-layer photosynthetic model was used to simulate the photosynthetic carbon sequestration capacity of Phyllostachys pubescens forest canopy,which provided a new tool for the subsequent analysis of efficient carbon sequestration mechanism and sustainable management of Phyllostachys pubescens forest.The main results are as follows:(1)The results of field experiments show that the biophysical and biochemical parameters of Phyllostachys pubescens forest canopy have obvious vertical changes.The new MRTM model can divide the Phyllostachys pubescens forest canopy into five vertical layers,which can cover the vertical heterogeneity in the canopy,so that the model can more effectively simulate the spectrum of Phyllostachys pubescens forest canopy and retrieve the vertical distribution of biophysical and biochemical parameters in the canopy.(2)The 5-layer MRTM model can well describe the vertical heterogeneity of Phyllostachys pubescens canopy,and the simulation accuracy is better than the other three homogeneous canopy models(PROSAIL,ACRM and FRT).This clearly shows that the biophysical and biochemical characteristics of Phyllostachys pubescens forests are quite different in the vertical direction,and the effects on canopy optical properties and photosynthesis can not be ignored.Therefore,compared with PROSAIL,ACRM,FRT and other homogeneous canopy models,the multi-layer canopy model proposed in this study has made progress to a certain extent.(3)Based on the multi-layer radiative transfer model developed in this study,combined with the leaf photosynthesis mechanism model,the canopy multi-layer photosynthetic model was obtained.Compared with the traditional "big leaf" and "two leaf" models,this model greatly improved the simulation accuracy of the canopy photosynthetic rate of Moso bamboo forest.In conclusion,the canopy of Phyllostachys pubescens forest usually shows great vertical heterogeneity in leaf biochemical and structural parameters.In some cases,the description of canopy by homogeneous model is not enough to accurately understand reflectance and canopy photosynthesis.In this study,a comprehensive model of radiation transfer and energy balance was proposed to solve the vertical heterogeneity of leaf biophysical and biochemical parameters in the canopy.MRTM model simulates the reflectance and Photosynthesis of vertical heterogeneous canopy,which can better understand remote sensing signals and plant physiology,and thus better simulate the photosynthetic carbon fixation capacity of Phyllostachys edulis canopy.