Vegetation stress: An introduction to the stress concept in plants

This is a presentation of the essentials of the present stress concept in plants, which has been well developed in the past 60 years. Any unfavorable condition or substance that affects or blocks a plant's metabolism, growth or development, is to be regarded as stress. Plant and vegetation stress can be induced by various natural and anthropogenic stress factors. One has to differentiate between short-term and long-term stress effects as well as between low stress events, which can be partially compensated for by acclimation, adaptation and repair mechanisms, and strong stress or chronic stress events causing considerable damage that may eventually lead to cell and plant death. The different stress syndrome responses of plants are summarized in a scheme. The major abiotic, biotic and anthropogenic stressors are listed. Some stress tolerance mechanisms are mentioned. Stress conditions and stress-induced damage in plants can be detected using the classical ecophysiological methods. In recent years various non-invasive methods sensing different parameters of the chlorophyll fluorescence have been developed to biomonitor stress constraints in plants and damage to their photosynthetic apparatus. These fluorescence methods can be applied repeatedly to the same leaf and plant, e.g. before and after stress events or during recovery. A new dimension in early stress detection in plants has been achieved by the novel high resolution fluorescence imaging analysis of plants, which not only senses the chlorophyll fluorescence, but also the bluegreen fluorescence emanating from epidermis cell walls which can change under stress induced strain. This powerful new technique opens new possibilities for stress detection in plants.