Microscopical investigations on wood formation and function in dlseased trees

Abstract

Histologieal and histochemical investigations were performed on the xylem, cambium, and phloem of Abies alba and Picea abies affected by forest decline ('Waldsterben', 'Neuartige Waldschäden'). In comparison to healthy trees the annual inerement was reduced and correspondingly the active cambial zone was smaller. No differenees were found in the peroxidase activities in the differentiating tracheids undergoing lignification, and no change in lignin content eould be deteeted UV-photometrieally in the walls of the traeheids of affeeted trees. In general, mueh less starch reserves in the paren-chymatous elements of the diseased trees were observed during autumn and spring. Correspondingly, the aetivities of enzymes involved in the mobilisation and transport of these earbohy-drates were lower in spring. With the use of fluorescent markers it eould be demonstrated that apparently some areas of the sapwood do not take part any longer in the water conduetion in diseased trees. In most eases differenees between healthy and diseased trees were much more pronounced in fir than in spruce. Furthermore, diseased firs showed a special pathological reaetion with the formation of large muei-lage cells in the non-funetional phloem and of oecasional traumatie resin canal barriers in the xylem.