Über die Bedeutung von Mikroorganismen im Holz von Abies alba Mill. für das Tannensterben

Eighteen healthy and thirty nine diseased firs (Abies alba Mill.) of young and old growth from four sites have been investigated by biological and micro-biological methods in order to contribute to the explanation of the fir dieback.The sapwood of diseased trees had a lower moisture content than that of healthy ones.The most striking alteration in the woody tissue of diseased trees is the development of wetwood which spreads irregularly into the sapwood, thus reducing the water-conducting area in the trunk considerably. This wetwood is most predominant in the butt and in the roots near the butt. It is always associated with bacteria which act on the parenchymatic cells by means of their metabolic substances such as acetic-, propionic-, and butyric acid. This in turn causes a decrease of the pH value of the capillary liquid from about 5.5–6.0 to 4.2. The most important strains of bacteria involved were identified asCorynebacterium (micro-aerophilic),Enterobacteria of the genusErwinia orKlebsiella, Staphylococcus (facultatively anaerobic),Clostridium and lactic acid producing bacteria (anaerobic). These bacteria were unable to consume components of the wood in vitro except for a hemicellulose. These bacteria infect the firs through existing wounds. In trees of already reduced vitality this induces a generalizing disease which may eventually lead to the tree’s death.