Investigation on the Nitrogen Metabolism of Spruce Needles in Relation to the Occurrence of Novel Forest Decline

Abstract

In order to obtain information on the nitrogen metabolism of undamaged and damaged spruce ( Picea abies ), investigations were performed in 1985 and 1986 on the activity of glutamine synthetase and on the content of free ammonium and soluble proteins in spruce needles. In addition, the chlorophyll content was determined. Needles from the second needle year and the seventh whorl were used. The investigations were carried out in pair comparison on a 20-year-old spruce plantation and in comparison with damage classes on an 80-year-old spruce plantation. Both the pair comparison and the contrasting of different damage groups show an unequivocal decrease of the chlorophyll content correlated with increasing damage to the trees. The chlorophyll content proves to be a reliable indicator of the overall extent of damage to the tree, even in apparently green needles. A rise in the content of soluble proteins in the green needles of the damaged trees was shown at both locations. A breakdown of soluble proteins was only observed in definitely yellow needles. The accumulation of soluble proteins in the damaged trees is correlated with the measured activities of ribulose bisphosphate carboxylase and glutamine synthetase. The needles of the damaged trees contain reduced levels of ammonium. Conversely the activity of glutamine synthetase showed a major rise, especially in 1985. The results contradict the assumption that the increase in activity of glutamine synthetase is associated with an elevated nitrogen supply. The lower content of free ammonium as well as the increase in soluble proteins associated with an increase of the glutamine synthetase activity may indicate a high protein turnover and a shift in the protein composition. This can be interpreted as a response to environmental stress and membrane damage in the cells.