昼夜不对称增温对冬小麦花后冠层反射光谱特性的影响

摘要

Global warming is one of the most important environmental issues today. Temperature data over the past ten decades show that the warming rate of the global land surface during the night is larger than that during the day. Temperature affects the growth condition of winter wheat (Triticum aestivum L.), and alters its canopy spectral reflectance. To our best knowledge, there are still rare researches on the asymmetric effects of daytime and nighttime warming on winter wheat canopy spectral reflectance. So this paper explored the asymmetric effects of daytime and nighttime warming on winter wheat canopy reflectance through experiments in an open field warming system. The experiment field is located at the agro-meteorological research station, Nanjing University of Information Science and Technology, Nanjing, China. Three treatments were carried out:asymmetry warming (daytime warming 1℃, nighttime warming 3℃, T2), symmetric warming (daytime warming 2℃, nighttime warming 2℃, T1), the control (CK), and two varieties of wheat Yangmai 15 and Xumai 31 were used. The ceramic heating lamps were used to heat the experimental plot. In order to ensure the warming effect, the work status of ceramic heating lamps was controlled by single-chip microcomputer. The ceramic heating lamps were hanged 40-50 cm above the wheat canopy to avoid harming wheat plants. The CK treatment also hanged the same ceramic heating lamps, but no power supply. Canopy reflectance was observed in the three treatments and the first derivative spectra were calculated. The canopy spectral reflectance of two varieties of winter wheat was measured by FieldSpec Pro FR spectrometer (ASD, USA). The results showed that winter wheat canopy reflectance of T2 significantly decreased in near infrared bands as compared to CK. Moreover, the canopy reflectance decreased more significantly in anthesis stage than in other growth stages. In anthesis stage, the reflectance of Yangmai 15 were 0.70, 0.61, 0.55 under T1, T2 and CK treatment in near infrared bands, while the reflectance of Xumai 31 were 0.65, 0.60, 0.52, respectively. The decrease pattern of T1 was similar to T2, but with smaller magnitude. The first derivative spectra showed that the red edge position of Yangmai 15 was 738 nm at the anthesis stage, and then shifted to 731 nm, 730 nm at 20 days after anthesis under T1, T2 treatment, respectively. Xumai 31 had the same rules. The decrease of red edge peak value in T1 and T2 was significant, especially in anthesis stage. Corresponding to the change of canopy spectral reflectance, Chlorophyll content of leaf and leaf area index of two varieties of winter wheat notably decreased in T1 treatment, especially in T2 treatment. Therefore, the changes of chlorophyll content of leaf and leaf area index, also the cell structure, resulted in the above variation in canopy spectral reflectance.%全球变暖具有明显的昼夜不对称性，温度升高影响冬小麦的生长发育，也改变了其冠层的光谱反射特性。为了研究昼夜不对称增温对冬小麦冠层反射光谱特性的影响，在南京采用开放式田间增温系统，开展昼夜不对称增温的人工控制试验，利用FieldSpec Pro FR光谱仪测定了2个冬小麦品种扬麦15和徐麦31的冠层反射光谱，分析了冬小麦开花后冠层光谱反射率和一阶导数光谱，比较了2种增温方式对冠层反射光谱特性的影响。结果表明，与CK相比，昼夜不对称增温处理（白天增温1℃，夜间增温3℃，T2）的冬小麦冠层反射率，在近红外波段的下降最为显著，且以开花期的冬小麦冠层近红外波段反射率降低幅度最大。昼夜对称增温处理（白天增温2℃，夜间增温2℃，T1）下的冬小麦冠层反射率变化与T2处理后的变化相似，但其反射率降低幅度小于T2处理。在开花期，扬麦15在CK、T1、T2处理下近红外波段反射率分别为0.70、0.61、0.55，而徐麦31在CK、T1、T2处理下近红外波段反射率分别为0.65、0.60、0.52。由一阶导数光谱可以发现，T1、T2处理下，扬麦15红边位置由738 nm变为花后20 d的731和730 nm，俆麦31表现相同的规律。T1和T2处理也使得红边峰值下降，在开花期红边峰值下降幅度最大，且T2处理下降幅度较T1处理更大。与光谱反射率变化相对应，T1和T2均使2品种的叶绿素质量分数和叶面积指数（leaf area index，LAI）显著降低，以T2处理降低幅度最大。因此，昼夜不对称增温影响了冬小麦LAI、叶绿素质量分数、细胞结构和衰老程度，进而表现出冬小麦冠层反射光谱反射率的下降。