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RESEARCH PRODUCT

Measurement of Photosynthesis and Transpiration in Spruce Trees with Various Degrees of Damage

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Summary In the context of a project on physiological and biochemical characterization of spruce with different degrees of damage, the C02 and H2O gas exchange of 22-year-old spruce from a location in the Hunsru.ck (West Germany) were measured in summer 1985. The measurements were carried out on shoots from 1984 and were set up as a pair comparison, i.e. the measurement data of a tree with symptoms of damage were always compared with a tree in the immediate vicinity which phenotypically showed less damage. Diurnal course measurements in the open air revealed a marked reduction of photosynthesis depending on the degree of damage of the trees. If one plots photosynthetic rate against light intensity, the slope of the linear part of the resulting curve expresses the efficiency of light utilization, which was reduced for the damaged trees. Also reduced were the daily maximum photosynthesis and the overall sum of photosynthetic rates per day and tree. On the other hand, the transpiration only differed to a small extent within the tree pairs. The light and C02 saturation curves measured in the laboratory showed a reduction of the light and C02 saturation values as well as a reduction of the efficiency of light utilization and of the carboxylation efficiency of the more severely damaged trees. A reduced supply of ATP and NADPH2 from the photosynthetic electron transport is discussed as a possible cause of the reduced photosynthesis. This might lead to a raised formation of activated oxygen species and finally to the damage of the biomembranes.