Variation of reflectance signatures of a leaf as indication of physiological activity

During illumination with strong white light the reflectance signature of a leaf undergoes slight changes within several s and min in the visible and near infrared. The authors present in vivo reflection spectra of different types of leaves (beech, fir, tobacco) measured between 400 and 900 nm within 100 ms by the VIRAF II spectrometer (VIRAF-Visible Infrared Reflectance Absorptance Fluorescence). Two types of changes can be observed: 1. Decrease in the reflectance with bands at 690 and 740 nm. This change reflects the decrease of chlorophyll fluorescence which parallels the increase of photosynthetic activity. 2. Slight increase of the reflectance in the whole visible range (mainly in tobacco leaves). This change reflects chloroplast movements which only occur in physiologically active cells. The significance of the slight changes of the reflectance signatures is discussed in view of a possible application in remotely detecting physiological activity of plants