The Nitrogen Economy of Myrica Gale in the Field

Abstract

SUMMARY (1) The growth and nitrogen content of Myrica gale have been measured over two growing seasons in a Myrica-Molinia community on relatively poorly aerated soil at a site in central Scotland. (2) The biomass and nitrogen content of Myrica were the same in early spring and late autumn. (3) Woody rhizomes accounted for 50-70% of the total biomass; during early spring (March-April) they contained c. 65% of the nitrogen in the plant, most of the rest being in aerial shoots. (4) Visible growth was preceded by a large transfer of nitrogen from old aerial stems and rhizomes to buds. (5) When the first leaves were opening (mid-June), a potential for reduction of acetylene developed in the nodules. It reached a peak in late July-early August and declined to zero in October. When the rate of acetylene reduction reached its peak, the net transfer of nitrogen from rhizomes to new shoots finally ceased. At this stage leaves contained c. 30% of the nitrogen in the plants. (6) Subsequently the nitrogen content of the rhizomes rose, and leaf nitrogen declined. By late October or early November all leaves were shed and the concentration of nitrogen in the rhizomes had returned to its early spring value. (7) The nitrogen lost from the plant in leaves is about 30 kg ha-' yr-. If there is no uptake of mineral nitrogen from the soil, an equivalent amount of nitrogen must be fixed.