Spectral response of rice (Oryza sativa L.) leaves to Fe2+ stress

In the management of lake eutrophication, the regulation effect of Fe is considered, in addition to the controlling nitrogen- and phosphorus input. Based on the “Fe hypothesis”, this paper tentatively ap-plied plant spectral response to the remote sensing early-warning mechanism of lake eutrophication. A laboratory water culture experiment with rice (Oryza sativa L.) was conducted to study Fe uptake by plants and the chlorophyll concentration and visible-near infrared spectrum of vegetable leaves as well as their interrelations under Fe²⁺ stress. Three spectral indices, i.e., A₁ (integral value of the changes of spectral reflectivity in the range 460―670 nm under Fe²⁺ stress), A₂ (integral value of the changes of spectral reflectivity in the range of 760―1000 nm under Fe²⁺ stress) and S (blue-shift range of red edge curve under Fe²⁺ stress), were used to establish quantitative models about the relationships between the rice leaf spectrum and Fe²⁺ stress. With the increase of Fe²⁺ in a culture solution, the Fe content in rice plants increased, while the chlorophyll concentration in vegetative leaves decreased. The spectral reflectivity of vegetable leaves increased in the visible light band but decreased in the near infrared band, and the blue-shift range of the red edge curve increased. The indices _A1, A₂ and S all had sig-nificant correlations with the Fe content in rice leaves, the correlation coefficient being respectively 0.951 (P < 0.01), −0.988 (P < 0.01) and 0.851 (P < 0.01), and simulated (multiple correlation coefficients R² > 0.96) and predict the Fe level in rice leaves.