Non-Contact Measurement Methods of Detecting Plant Water Deficit Stress for Space Flight Growth Chamber Application

This study investigated the possibility of detecting water deficit stress in plants by using optical signals collected from leaves. Two theoretical approaches have been investigated. In principle, chlorophyll fluorescence can be used to measure generally stressful situations in plants. Our review, however, found that simple ratios of coarsely time-resolved chlorophyll fluorescence, such as maximum fluorescence over fluorescence at steady state, appear to be incapable of adequately distinguishing water stress from other stress factors. A second principle being investigated involves correlation of light absorption within leaves to leaf-water-content using water absorbing and non-water absorbing wavelengths. Our investigation concentrated on defining and eliminating as many extraneous variables as possible. Applying a dual-wavelength method in the near-infrared range, our data thus far indicate that this principle promises success for distinctively detecting water deficit stress of individual plants grown in space flight chambers.