Oak decline has often been associated with root infections by Phytophthora pathogens. This study addresses the ecophysiology of the aboveground decline in trees displaying root infection. Mature trees of an oak stand (Quercus robur L.) near Landau-on-Isar/Germany showing all stages of apparently healthy and yellowing foliage. These trees were analysed for their photosynthetic performance, water relations, stomatal regulation, nutritional status, pigments of chloroplasts, phenology and annual ring formation. In the clayey, fluvial soil Phythothora ssp. were isolated, regardless of leaf discolouration, from the root system of the study trees, although the extent of infection differed. Water potential was not decreased in yellowing trees, although root axes could have lost up to 70 % of their fine roots. However, stomata tended to be narrowed along with the decline in chlorophyll concentration. The latter rather than the electron transport through the chlorophyll restricted the photosynthetic capacity and the carboxylation efficiency. Pigment loss was not related to nutrition, although the soil properties caused low levels of manganese and iron in the leaves. Annual ring formation has declined in those trees being most restricted by yellow crowns since 1980, although soil water conditions have been adequate throughout the years. It is concluded that the tree crowns do not suffer primarily from the fine-root loss and internally induced drought. Rather, injury may arise from photoinhibitory effects through induced partial stomatal closure.     «

Oak decline has often been associated with root infections by Phytophthora pathogens. This study addresses the ecophysiology of the aboveground decline in trees displaying root infection. Mature trees of an oak stand (Quercus robur L.) near Landau-on-Isar/Germany showing all stages of apparently healthy and yellowing foliage. These trees were analysed for their photosynthetic performance, water relations, stomatal regulation, nutritional status, pigments of chloroplasts, phenology and annual rin...     »