This study proposed a new vegetation index ADVI to detect the pollution degree of different varieties of maize under copper stress, which provides a new idea for the detection of heavy metal pollution in vegetation. In order to ensure the outdoor growth environment of maize, we put all maize into outdoor greenhouse. The spectral reflectance interval of 450–850 nm of maize leaves was processed by the absorbance conversion ( A ) and the first-order differential ( D ), and the absorbance differential (AD) spectral curve was obtained. The Pearson correlation coefficient ( r ) was used to analyze the AD data and the biochemical data and select characteristic bands that are sensitive to heavy metal copper (Cu). The calculated Pearson correlation coefficients suggested that the AD value at 547–553 nm and 672–674 nm presented a linear positive correlation close to 1 with the Cu 2+ contents in soil and leaves, and a linear negative correlation close to − 1 was present in the range of 496–506 nm and 677–679 nm. We selected the AD value of wavelengths 501 nm, 550 nm, 673 nm, and 678 nm to establish ADVI and compared it with conventional vegetation indices (VIs) by calculating Pearson correlation coefficient between them and Cu contents in soil and leaves, and vegetation indices include Water Band Index (WBI), Photochemical Reflectance Index (PRI), MERIS Terrestrial Chlorophyll Index (MTCI), Modified Red Edge Simple Ratio Index (mSR), Modified Chlorophyll Absorption Ratio Index (MCARI), Water Index (WI), Normalized Difference Water Index (NDWI). Maize leaf spectral data obtained from experiments in 2017 were used for verification, and ADVI was also compared with WBI, PRI, MTCI, mSR, MCARI, WI, and NDWI. The calculated Pearson correlation coefficient between ADVI and Cu 2+ contents in soil and leaves is 0.9816 and 0.9460 (experimental data of 2016). The calculated Pearson correlation coefficient between ADVI and Cu 2+ contents in soil and leaves is 0.9109 and 0.9639 (experimental data of 2017). The results suggested that ADVI showed a significant correlation with Cu 2+ stress concentration, and the correlation of ADVI was much stronger than that of other vegetation indices. The proposed ADVI detects the pollution degree of maize with different varieties and in different periods under copper stress has advantages of straightforward calculation, robustness, and high effectiveness. This study focused on the laboratory leaf scale, so it is expected that future work extends it to a wide range of field scale and image scale.

中文翻译：

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铜胁迫下玉米污染程度的监测

本研究提出了一种新的植被指数ADVI来检测铜胁迫下不同品种玉米的污染程度，为植被重金属污染检测提供了新思路。为了保证玉米的室外生长环境，我们将玉米全部放在室外温室中。通过吸光度转换（ A ）和一阶微分（ D ）处理玉米叶片450-850 nm光谱反射区间，得到吸光度微分（AD）光谱曲线。使用皮尔逊相关系数 (r) 分析 AD 数据和生化数据，选择对重金属铜 (Cu) 敏感的特征条带。计算的Pearson相关系数表明，547-553 nm和672-674 nm处的AD值与土壤和叶片中Cu 2+ 含量呈接近1的线性正相关，呈接近-1的线性负相关在 496-506 nm 和 677-679 nm 范围内。我们选取波长501 nm、550 nm、673 nm和678 nm的AD值建立ADVI，并通过计算它们与土壤和叶片中Cu含量和植被指数的Pearson相关系数与常规植被指数（VIs）进行比较包括水带指数（WBI）、光化学反射指数（PRI）、MERIS陆地叶绿素指数（MTCI）、修正红边简单比率指数（mSR）、修正叶绿素吸收比指数（MCARI）、水分指数（WI）、归一化差水指数（NDWI）。使用2017年实验获得的玉米叶片光谱数据进行验证，同时将ADVI与WBI、PRI、MTCI、mSR、MCARI、WI和NDWI进行比较。计算得到的土壤和叶片中ADVI与Cu 2+ 含量的Pearson相关系数分别为0.9816和0.9460（2016年实验数据）。计算得到的土壤和叶片中ADVI与Cu 2+ 含量的Pearson相关系数分别为0.9109和0.9639（2017年实验数据）。结果表明，ADVI与Cu 2+ 胁迫浓度呈显着相关，且ADVI的相关性远强于其他植被指数。提出的ADVI检测铜胁迫下不同品种、不同时期玉米的污染程度，具有计算简单、鲁棒性强、有效性高等优点。