铜胁迫下玉米叶片光谱谐波振幅特征与胁迫程度判别

Harmonic Amplitude Characteristics of Maize Leaves Reflectance and Stress Degree Discrimination under Copper Stress

为探测重金属铜污染胁迫对玉米叶片光谱的影响,判别玉米植株受铜污染胁迫的程度,在地面设置了11个梯度铜胁迫玉米盆栽实验,获取了玉米在出苗期、拔节期和出穗期的老叶光谱、叶绿素含量以及出穗期叶片铜含量,阐述了利用前3次谐波子信号振幅C1、C2与C3探测玉米叶片光谱弱畸变的机理,并选取出苗期、拔节期和出穗期玉米老叶光谱480~670 nm与670~750 nm两波段进行谐波分析,解析了前3次谐波子信号振幅C1、C2、C3与铜胁迫梯度间的规律。研究得出:出苗期,在Cu(100)到Cu(1200)梯度范围内,随铜胁迫程度增加,玉米老叶光谱在480~670 nm与670~750 nm两波段的谐波振幅C1逐渐增大,利用谐波振幅C1可以判别与区分玉米植株受铜胁迫程度;拔节期,在480~670 nm与670~750 nm两波段、所有设置胁迫梯度内,谐波振幅C1、C2、C3特征变化规律不明显;出穗期,从Cu(50)到Cu(1200)梯度范围内,除Cu(1000)外,在480~670 nm波段的谐波子信号振幅C1随胁迫梯度增加而增大;玉米出苗期与出穗期是利用谐波子信号振幅特征进行铜胁迫程度判别与分析的最佳生长阶段。

The effect of heavy metal copper stress on maize leaves reflectance is weak, hidden and difficult to be detected. To analyze the spectral response of maize leaves to copper stress and discriminate the stress degree on maize plant, the pot experiment with 11 copper stress gradients was set at ground laboratory, the maize leaves reflectance and chlorophyll content were obtained at seedling stage, jointing stage and heading stage. The copper content in leaves was also gotten at heading stage. At 480~ 670 nm and 670~750 nm, the spectra simulated under the conditions of normal growth, low concentration stress and high concentration stress were constructed respectively. The mechanism of using the first three harmonic amplitudes C 1 , C 2 and C 3 to detect the weak spectral distortion in maize leaves reflectance under copper stress was analyzed. The harmonic analysis was carried out in two wavelength ranges of 480~ 670 nm and 670~750 nm at seedling stage, jointing stage and heading stage, and the rule between the amplitudes C 1 , C 2 and C 3 and the copper stress gradient was also analyzed. The results showed that at the seedling stage, in the gradient range of Cu(100) to Cu(1200), with the increase of copper stress gradient, the harmonic amplitude C 1 of old leaves reflectance of 480~670 nm and 670~750 nm was increased, and in the gradient range of Cu(100) to Cu(1200), the harmonic amplitude C 1 could be used to distinguish the degree of copper stress on maize plant. At heading stage, from Cu(50) to Cu(1200), except for Cu(1000) gradient, the harmonic amplitude C 1 of 480~670 nm was increased with copper stress gradient. At jointing stage, for the bands of 480~670 nm and 670~750 nm, the variation of the harmonic amplitudes C 1 , C 2 and C 3 was not obvious in all stress gradients. The seedling stage and heading stage were the best growth stages for monitoring copper stress on maize plants by harmonic amplitude characteristics. The method proposed was designed and tested at leaf scale, and further study were also needed to evaluate its potential at canopy scale. The method proposed provided a potential basis for other applications by using airborne and satellite remote sensing data.