本文设计了大豆(C3作物)和玉米(C4作物)日变化光谱探测试验,提取了太阳光照条件下叶绿素荧光信号和光化学指数PRI。结果表明,首先大豆和玉米叶绿素荧光强度的日变化特征有较大差异,上午大豆的叶绿素荧光比例呈现快速增加的趋势,而玉米的叶绿素荧光未出现增加趋势;其次,下午高温胁迫条件下C3、C4叶绿素荧光光谱比值的变化差异显著,大豆在760 nm和688 nm波段的叶绿素荧光比值快速增加,而玉米未出现显著变化;最后,研究证实了C3作物中午受到强光抑制出现光合作用“午休”现象,即午后光合恢复后其光合效率快速增加,表现为C3作物的热耗散降低、PRI快速增加,而C4作物无“午休”现象,午后PRI增加较小。本文研究表明,强光和高温环境胁迫下C3、C4作物的叶绿素荧光和热耗散变化特征有较大差异,利用胁迫条件下的多时相、高光谱遥感数据,提取C3、C4作物的叶绿素荧光和PRI,有可能实现C3、C4作物的遥感分类目标。

The classif ication of C3 and C4 plant functional types has become an important issue in global change research, butthe mechanism of using remote sensing data remains unclear. In this paper, a diurnal variation experiment was designed for soybean(C3 plant functional type)and maize(C4 plant functional type)to acquire canopy spectra under different illumination andtemperature conditions, and chlorophyll fl uorescence(ChlF)signals and photochemical refl ectance index(PRI)were extractedfrom the canopy spectra. The results showed that:(1)the amplitudes of the diurnal variation in ChlF between soybean and maizewere signif icantly different, as the relative ChlF of soybean increased rapidly under heat and high irradiance stresses in theafternoon, but the increasing trend was not found in maize;(2)there was also an apparent increase in the ratio f688/f760 of ChlFintensities of soybean in the afternoon, but this did not appear in maize;(3)the midday photosynthetic depression occurred in C3crops owing to the stressed light and temperature, with a rapid increase in PRI. However, there was no apparent noon depressionin C4 crops. Based on the different characteristics between the responses of C3 and C4 crops to high irradiance and temperaturestressws, we proposed a potential method to discriminate C3 and C4 plants by multitemporal and hyper spectral remote sensingdata.