Spectral response of cotton to suddenly induced water stress

Abstract

Spectral responses in eight wavebands (three visible, two near-IR, two mid-IR, and one thermal IR) were measured by repetitively traversing a radiometer over several rows of cotton (Gossypium hirsutum L.). After an initial measurement, the stems of one row (which had previously been tied to wooden dowels) were cut at a point just above the soil. The subsequent dessication of plants within this row was followed by comparing its reflectance and emittance with a control row. All wavebands measured reacted rapidly to stress with the visible and thermal IR showing a larger change than the near-IR. Reflectance changes caused by canopy geometry changes were apparently greater than those caused by leaf physiological and anatomical changes in all but the visible red band. The increase in red reflectance was attributed to a rapid decrease in absorptance by leaf chloroplasts. As expected, the radiometrically determined plant temperatures increased with time after the stress was imposed.