Monitoring of the Status of Alpine Forests by Complex Responses of Physiological Variables in Spruce Needles : Research and Monitoring as Key Elements for the Sustainable Development of the Limestone Alps European Strategies
The impact of various kinds of environmental stresses on plants cause an enhanced production of toxic oxygen species and free radicals in the cells (oxidative stress). Components of the antioxidative defence system, such as ascorbate, glutathione, tocopherol, or antioxidative enzyme activites (e.g. peroxidases) are responsible for the scavenging of these toxic substances. These variables together with chloroplast pigments (chlorophylls and carotenoids) respond in typical ways to different kinds of environmental stresses. Under field conditions, environmental influences on forest trees are complex and cause complex stress situations. Daily fluctuations of physiological variables responding to environmental influences refelect mostly the influence of light and the development of photoinhibition. Taking inot account daily and seasonal fluctuations in form of standardised sampling procedures it is possible to compare different field stands. In some mountainous ecosystems there is a pronounced altitude gradient of environmental stress: Trees at higher altitudes are exposed to an incrased level of oxidative stress caused by a combination of harsher climate, higher irradiation, and higher ozone levels. Plant responses to this situation include elevated concentrations of antioxidants (in particular ascorbic acid, but to a less extent also glutathione) and decreases in chloroplast pigment contents. Such responses were observed repetatedly in both the Limestone and the Central Alps (on Picea abies growing at sea levels of 600 m up to more than 1700 m a.s.l.). However, such main ecological gradients are often covered by other factors, such as edaphic or meteorological conditions. Through a classification of patterns of physiological responses by multivariate statistics, differences and similarities among field stands can be worked out objectively. The evaluation of physiological responses of the plants allow an assessment of the extent to which trees at a given field stand suffer under stress conditions.
