Manganese-induced physiological iron deficiency in Douglas Fir

Abstract

Since the middle of the sixties, an apparently new disease affecting Douglas fir (Pseudotsuga menziesii var. viridis) is observed in SW-Germany. Symptoms of this disease, which is obviously not primarily caused by fungal or other pathogens, are needle chlorosis, crown thinning, stem resin efflux, and growth anomalies. Based on needle analyses, an excessive uptake of manganese is discussed as the main cause of the disease. Because the patterns of needle chlorosis in affected trees are quite similar to an iron deficiency chlorosis, a close examination of the iron balance seemed to be of great interest. For comparison, trees from healthy and diseased natural Douglas fir were studied. The investigation also included a Douglas fir stand on calcareous soil, showing symptoms of a `true¿ lime-induced iron deficiency. Douglas fir trees bearing symptoms of the `new¿ disease type showed high and age-dependent increasing amounts of manganese in their needles, while the total needle iron contents were sufficient according to forestry experience. Despite of sufficient total iron contents, the amount of soluble iron was significantly decreased and the redox state of iron ions was altered in damaged Douglas fir trees, as compared to their healthy counterparts. Corresponding to this presumable `physiological¿ iron deficiency, iron dependent parameters like chlorophyll content and catalase activity were also affected in needles of diseased trees, as well as chloroplast ultrastructure.