PHOTOSYNTHESIS AND TRANSPIRATION IN DAMAGED AND UNDAMAGED SPRUCE TREES

The investigations presented here focus on the CO2/H2O gas exchange in damaged and undamaged spruce trees while using open-air measurements as well as measurements under defined conditions in the laboratory. Th e studies were performed at two different sites in the Hunsruck and th e Westerwald mountains. In the laboratory the CO2/H2O pas exchange was measured on detached branches under controlled conditions in the cour se of two years. CO2 saturation curves were also generated. In additio n CO2 compensation points were determined employing a closed system. I n the natural habitat diurnal course measurements of photosynthesis an d transpiration as well as light-saturation curves for photosynthesis were performed. In parallel with the photosynthesis and transpiration measurements, measurements of the water potential were taken at both l ocations. The photosynthetic capacity and transpiration rate show a ty pical annual course with pronounced maxima in spring and late summer a nd minima in summer and winter. The needles of the damaged trees exhib it higher transpiration rates and a distinct reduction in photosynthes is than the needles of the undamaged trees during two seasons. The diu rnal course measurements of net photosynthesis and transpiration show a maximum in photosynthesis and transpiration in the afternoon in May and September, but a characteristic midday depression in July. Photosy nthesis was markedly lower and transpiration higher in the needles of the damaged trees. The damaged trees show a lower increase in the ligh t and CO2 saturation curves and higher CO2 compensation points as comp ared to the undamaged trees. The water potential reaches much lower va lues during the course of the day in needles of the damaged trees. The reduction of the photosynthetic rate on one hand and the increase in transpiration on the other hand result in an extreme lowering of the w ater use efficiency in photosynthesis. The damage to the thylakoid mem branes and to the guard cells obviously results in a profound disturba nce of the physiological homeostasis of the needles and could thus lea d to premature needle loss.