Photosynthese und Naehrstoffversorgung von Fichten aus einem Waldschadensgebiet auf basenarmem Untergrund

1989

32 Abb., 58 Lit. Ang.

Unselbständiges Werk

4223

200021027

This article gives a survey of our investigations in the last four years dealing with the problem of forest dcline in the mountain areas of W- Germany. Most of our work was done at an experimental site near Oberwarmensteinach in the Fichtelgebirge (NE-Bavaria), where spruce (Picea abies (L.) Karst.) is heavily affected by forest decline phenomena. The typical, visible symptoms are yellow-chlorotic needles in addition to branch and needle loss. The Fichtelgebirge area is known for its high S02 impact and its soils, which are poorly supplied with certain nutrient elements such as Ca, Mg, and Zn. Within the "Bayerische Forschungsgruppe Forsttoxikologie" we have focuses on gas exchange measurements of apparently healthy-looking, green und damaged, yellow-chlorotic spruce trees. The photosynthetic performance was found to be correlated with the mineral nutrition of the needles. The main question was whether air pollutants directly affect the above-ground biomass of the plants, or whether the damage of the trees is primarly caused through acidification of the soil. Undernormal ambient conditions the damaged needles exhibit reduced rates of CO2 assimilation which seemed to be due to a decrease in the biochemical-biophysical capacity of the photosynthetic appartus rather than to a reduced stomatal conductance. This view is supported by comparing CO2 and light response curves of green and yellow needles. Damaged twigs exhibit a lower photosynthetic capacity (Pm, maximal photosynthetic rate at light- and CO2- saturation) as well as a reduced carboxylation efficienty (CE) and light use efficiency. Aan examination of the photosynthetic performance of healthy and damaged trees in the different needle age classes revealed that there is a strong depression of photosynthetic capacity and carboxylation efficiency of the chlorotic needles, but apparently no progression in the relative amount of damage with increasing age of the neddles. Thus the reduction of photosynthesis does not follow a dose-response relationship, i. e. is not dependant on the time of exposure of the twigs in the polluted atmosphere. This leads to the hypothesis that the damage occurs mainly in one or two steps within the life cycle of the needles and seems to be correlated only with their imbalanced mineral nutrition. Yellow needles show a significantly reduced amount of the element Mg as well as of Ca, Mn, and Zn, whereas the concentrations of K and Al are significantly increased. No differences between healthy and damaged spruce trees are apparent in the amount of S. Seasonally there is a large drop in the concentration of Mg in the older twigs of damaged trees at the time of the development of the new flush. As a result this shift of nutrient elements may lead to disturbances in the mineral nutrition of damaged trees causing needle chlorosis and a depression in the capacity for .......