Evaluation of chlorophyll fluorescence as a probe for drought stress in willow leaves.

The effect of drought on the photosynthetic apparatus of leaves of Salix sp. was studied by measurements of the induction of chlorophyll fluorescence and the capacity for O(2) evolution. Using a multivariate analysis, a model was developed that could predict the degree of drought stress from the data of fluorescence kinetics. Even mild drought stress was detected with high precision; this was not always possible when the photosynthetic capacity was measured. The most clear discrimination between control and drought-stressed leaves was obtained if fluorescence induction was measured at high rather than normal CO(2) levels, and at low rather than high light levels. All information provided by fluorescence pertaining to drought was contained within the slow phase of the induction curve. It is suggested that rapid dehydration is different from drought at the mechanistic level as judged by the fluorescence characteristics.