Remote Sensing Study of the Influence of Different Herbicides on the Leaf Spectral Reflectance and Fluorescence of Pea Plants (Pisum sativum L.)

The effective use of airborne and satellite-based remote sensor systems in resource management, agriculture, mineral exploration and environmental monitoring requires an understanding of the nature and limitations of the high-resolution remote sensing data and of various strategies for processing and interpreting it. In developing the necessary knowledge base, ground-based measurements are the expedient source of information. In this study, remote sensing techniques were applied in laboratory for detection of the influence of herbicides 2.4-D, glyphosate, fluridone and acifluorfen on the leaf spectral reflectance and fluorescence of pea plants (Pisum sativum L.). According to the classification of the Herbicide Resistance Action Committee with reference to their mode of action they belong to different groups: synthetic auxins - O (2.4-D), inhibition of EPSP synthase - G (glyphosate), photobleaching - F1 (fluridone), and inhibition of PPO - E (acifluorfen). During the last 40 years, these herbicides are among the ones used most widely in agriculture worldwide. The plants studied were grown hydroponically in a growth chamber in a nutritious medium to which every herbicide was added at two low concentrations (1 µM, 0.1 µM) with respect to the field dose applied in the agricultural practice. High-resolution spectral data for leaf spectral reflectance and fluorescence were collected from freshly detached leaves using three multichannel spectrometers. Spectral reflectance characteristics were obtained from the leaf reflectance referenced against a standard (white diffuse screen) in the visible and near infrared ranges of the electromagnetic spectrum (450÷850 nm). Fluorescence spectra were taken in the spectral range 650-850 nm. To assess the changes arising in leaf spectral reflectance under the herbicide action we developed and applied an analytical approach based on discriminant analysis and other statistical methods. The spectral characteristics were analyzed in four specific for the green vegetation spectral intervals: 520÷580 nm (maximal reflectivity region), 640-680 nm (maximal leaf absorption region), 690÷720 nm (red edge region) and 730÷770 nm (near infrared region). Statistically significant differences were found between the spectral reflectance characteristics of leaves of control and treated with herbicides plants at a significance level p¡0.05 for all concentrations of every herbicide except for the low acifluorfen concentration. The differences in the fluorescence spectra were assessed by several indices. A comparative analysis of the influence of the applied herbicides on the spectral reflectance characteristics and the fluorescence was performed. The results render the possibility to clarify the sensitivity of spectral features as a tool to assess the physiological responses and adaptation of plants to changes in environment.