| Atmospheric ozone layer is constantly depleted by human activities,which leads to the enhancement of ultraviolet radiation on the earth surface.Elevated UV-B radiation effects on crop growth is a crucial issue in the reach of global change.Silicon is a beneficial element for crop growth,and can promote crop development and improve its resistance to stresses,also alleviate the depressive effect of elevated UV-B radiation on crop growth.A field experiment was conducted to observe the canopy spectra of rice and wheat by using ASD FieldSpec Hand Held spectrometer on typical sunny days,and simultaneously to measure leaf area index(LAI)?relative chlorophyll content(SPAD value)and the above-ground fresh biomass of rice,and further analyze the characteristics of red edge parameters by calculating the first derivative spectra,the correlations between the canopy,first derivative spectra and physiological parameters at main growth stages under elevated UV-B radiation and silicate supply.The main results are listed as follows:(1)Growth and spectroscopy characteristics of rice and wheatThe results indicated that LAI,relative chlorophyll content(SPAD value)of two crops and above-ground fresh biomass of rice were decreased under elevated UV-B radiation,but silicate supply alleviated the depressive effect of elevated UV-B radiation on rice and wheat growth.The differences in canopy spectra of rice and wheat were mainly reflected in near-infrared band between the treatments,the reflectance of near-infrared band was decreased under UV-B radiation,but increased under silicate supply.The red edge position showed blue shift under elevated UV-B radiation and red shift under silicate supply.The red edge parameters of rice and wheat(i.e.red edge position,red edge amplitude and red edge area)showed a trend with an increase firstly and then a decrease,and the maximum occurred in rice at jointing stage,but in wheat at flowering stage.(2)The correlation coefficients between physiological parameters and spectra of rice and wheatThe correlation coefficient between canopy spectroscopy and LAI was negative in visible band for rice and wheat;and from negative to positive in red edge area;and was positive in near-infrared band.The correlation coefficient between canopy spectroscopy and SPAD value was similar to that between canopy spectroscopy and LAI.The correlation coefficient of LAI and SPAD value has a lager increase in major bands after the first derivative transformation.The correlation coefficients between spectrum variables and LAI were over 0.50(spectrum variables of rice:?r,?g/?r,?r,?503,?'741,?'456,?634,SDg,(SDr-SDy)/(SDr+SDy),pg and SDr/SDy;Spectrum variables of wheat:?'880,(pg-pr)/(pg+pr),?'683 and ?'786).The correlation coefficients between spectrum variables and SPAD value were over 0.50(spectrum variables of rice:?r,?r and pg/pr;spectrum variables of wheat:?'535,?'1017,?'547,?'670,SDr,(SDr-SDb)/(SDr+SDb),Dr,SDg,Db,?966,?1150 and ?g),and these correlation coefficients all were significant at a level of 0.01.(3)Estimation of physiological parametersBased on the spectra variables and estimated physiological parameters,it was better to use the spectra position variable p'741 and p'786 to estimate LAI of rice and wheat respectively,the estimation equations were yLAI-Rice=-32065x2+726.48x+0.3473 ?yLAI-Wheat=3.8207e904.46x;The spectra area variable SDb and position variable Db was used to estimate SPAD value in rice and wheat,the estimation equations were ySPAD-Rice=-6.1671Ln(x)+19.933 and ySPAD-Wheat=7E+06x2-28429x+75.859;LAI was used to estimate the above-ground fresh weight at grain-filling stage,the estimation equation was yabove-ground?-8.2523x2+82746x-151.23. |
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