GROWTH, METABOLIC COMPONENTS AND DROUGHT SURVIVAL OF LODGEPOLE PINE SEEDLINGS AT THREE NITRATE LEVELS

Abstract

Lodgepole pine (Pinus contorta Dougl. var. latifolia) seedlings were grown for six weeks in a controlled environment using nutrient solutions containing 0.4, 4.0 or 8.0 meq/liter nitrate-N. Increased nitrate supply resulted in plants with smaller root/leaf weight ratios and higher moisture contents in the leaves. Increased nitrate also brought about decreases in the soluble carbohydrate and starch contents of the leaves and roots; these changes were associated with higher amino-N and insoluble protein contents, especially in the leaves, but lower soluble protein contents. The results support the hypothesis that increasing the nitrate supply altered the metabolism of the seedlings by increasing the competition for reductant in the plants.Drought survival was assessed by the extent of new root growth following a period of drought and recovery. Seedlings grown at the highest nitrate level had the lowest survival when the three treatments were held without watering for a two-week period. However, nitrate level altered drought survival less if the three treatments were stressed to the same final moisture content in the growth medium.