Estimation Study Of Rice Canopy Photosynthetic Parameters Based On Remote Sensing And Model

Crop canopy morphology directly affects light radiation transmission and distribution inside the canopy,thus affecting crop photosynthesis and the ability to produce dry matter.The crop gross primary productivity(GPP)is the ability of green plants to convert absorbed carbon dioxide into accumulated dry matter by photosynthesis.Photosynthesis,light use efficiency(LUE)and canopy productivity are the basis for crop yield and quality.Therefore,real-time quantitative monitoring and prediction photosynthetic parameters,LUE and GPP has great significance for understanding the crops growth status and predicting yield and quality.In this study,two kind of rice with different plant type(Oryza sativa L.)where were choosed as experimental materials and field experiments were conducted in RuGao,involving different transplanting densities and nitrogen rates.Models of leaf layer photosynthetic rate and canopy LUE were constructed based on hyper-spectral and UAV multispectral vegetation index,and obtain daily variation of leaf layer photosynthetic rate and the difference of GPP on both sides of the canopy.Photosynthesis is an important factor for crop growth and development.It is important to study canopy photosynthetic rate for estimating dry matter weight,especially daily variation of canopy photosynthetic rate.The leaves light response curves of different positions under different periods showed variety of rectangular hyperbola.The leaves maximum net photosynthetic rate(Pnmax)and initial quantum efficiency(α)were obtained by fitting the light response curve,Pnc-max and a of leaf layers were obtained by the Gauss integral method.The maximum net photosynthetic rate and initial quantum efficiency of leaves and leaf layers show single peak variety during growth period,and significantly higher than low nitrogen under high nitrogen treatment.The relationship between Pnc,Pnc-max,αand the multi-spectral vegetation index of UAV showed that the Modified structurally insensitive pigment index SIPIm(R720-R550)/(R800-R680)have the best correction with Pnc,Pnc-max,α,R2 are 0.74,0.72 and 0.61,respectively.The leaf layers light response model was obtained by Pnc-max,α(were obtained by using the UAV spectral index)and Rd(was obtained by summing the Rd of leaves).The daily photosynthetically active radiation(PAR)measured by QSO-S PAR sensor is the input parameter to predict the daily photosynthetic rate based on multi-spectral vegetation index.When study canopy GPP,we find it was mainly affected by canopy LUE and APAR.The canopy LUE was obtained by CASA model,CASA model only considers the effects of temperature and moisture.This study add nitrogen stress to CASA model,and the ratio of canopy nitrogen content to maximum nitrogen content as nitrogen stress factor f(N),and were used to quantify the effect of nitrogen on rice LUE.f(N)increasing first and decreasing during the whole growth period.Considering the difference of canopy APAR distribution when simulate canopy APAR,especially the difference in the shaded leaves and light leaves of APAR,APAR and FAPAR of shadow side are significantly higher than the light side.By studying the relationship between hyper-spectral vegetation index and APAR and FAPAR of canopy both side showed the better correlation between APAR and FAPAR of shadow side and vegetation index,especially the R2 of NDVI(R915,R710)and FAPARs reached 0.78.The dynamic variety of canopy GPP on both side is obtained by APAR(obtained from the canopy hyper-spectral vegetation index)and LUE(obtained by modified CASA model).The results showed that GPPs of shadow side is significantly higher than the light side,and variation amplitude is smaller during the whole growth period,and the R2 of canopy leaf dry weight before filling is 0.78.