Long-Term Monitoring of Nitrate Reductase Activity in the Needles of Pinus sylvestris in the Context of Environmental Temperature and Ground Frost as an Indicator of Nitrogen Balance in N. Finland

1991

1 Abb., 14 Lit. Ang.

Unselbständiges Werk

4570

200048382

Nitrate reductase (NR) activity in Pinus sylvestris needles showed seasonal fluctuations, being very low (0.1-0.5 nkat x kg-1 protein) during the summer months (June-August) and reaching its maxima (1-2 nkat) during the autumn and winter (September-March). Winter time acticity was highest in the youngest needles, and became lower the older the needles were, while there were no differences in summer time activity. The NR activity of the needles was greatly dependent on frost and temperature conditions. In 1987 the summer was cold and the frost melted from the ground slowly, which meant that foliar NR activity was low throughout the year, and imbalance which continued into 1988. The growth of the pines also suffered a serious setback during this period and many trees died. One reason for this could have been an imbalance in nitrogen metablism, due to the exceptionally low activity of at least one key enzyme of nitrogen metabolism, NR.