Dynamic Simulation Of Net Photosynthetic Rate Of Artificial Larix Olgensis Crown

The research objects of this paper was the Larix olgensis plantation in Maoershan Experimental Forest Farm of Northeast Forestry University and Xiaojiu Forest Farm of Shangzhi,the net photosynthetic rate of the crown was simulated dynamically which based on the photosynthetically active radiation data and light response curve data measured in the growing season of 2018.Firstly,the actual extinction coefficients of the various layers in the crown were calculated based on Lambert-Beer law,and the best fixed value of the extinction coefficient was determined using the assignment method.Analyze other variables that affect the extinction coefficient,and establish a crown light distribution model in combination with Lambert-Beer law.Secondly,This study screened the best light response curve model,and studied the relationship between the model parameters and leaf temperature,water vapor pressure deficit,specific leaf weight,and relative depth into crown,we established a crown light response curve model.The specific results were as follows:The extinction coefficients of the crown layers calculated from Lambert-Beer law and measured photosynthetically active radiation data were between 0.1 and 1.5 and had a positive correlation with the relative depth into crown.The best fixed value of extinction coefficient was 0.32 which was determined by the assignment method.At the same time,Meanwhile,solar altitude angle,max cumulative leaf area,needle area density,and crown surface area also had significant effects on extinction coefficient.Therefore,the above variables were parameterized and combined with Lambert-Beer law,a canopy light distribution model was established.the model performed well R2=0.736,RMSE=0.124?mol m-2 s-1.In this study,the simulation effect of photosynthetically active radiation in the crown predicted by the crown light distribution model was better,that ME=2.88?mol m-2s-1,MAE=117.4 ?mol m-2s-1,P=91.53%.The simulation effect of internal photosynthetically active radiation was the worst,that ME=-7.2?mol m-2s-1,MAE=217.5?mol m-2s-1,P=88.12%.The extinction coefficient was not a fixed value under different forests,different layers,and different solar altitude angle.The crown light distribution model established in this study takes into account the above three important variables,which was in line with objective reality.This model estimated that the photosynthetically active radiation in the crown has a good effect,and provided a basis for simulating the net photosynthetic rate at different positions in the crown.Comparing the fitting effects of the three models of modified rectangle hyperbola(MRH),modified exponential model(MEM),and Mischerlich function(M),the M model was selected as the best model for this study.Based on the relationship between the Maximum net photosynthetic rate,Apparent quantum yield,and Dark respiration and leaf temperature,water vapor pressure deficit,specific leaf weight,and relative depth into crown?Then,leaf temperature,water vapor pressure deficit,specific leaf weight,and relative depth into crown were parameterized to establish a crown light response curve model.Using this model to fit light corresponding curve data at different positions in the crown of Larix olgensis,R2=0.759,RMSE=1.840?mol m-2s-1.Verifying the canopy light response curve model using test samples,ME=0.047?mol m-2s-1,MAE=1.535?mol m-2s-1,P=95.98%.The model fits well.