Nitrate Nutrition and Temperature Effects on Wheat: a Synthesis of Plant Growth and Nitrogen Uptake in Relation to Metabolic and Physiological Processes

Lawlor, D. W., Boyle, F. A., Keys, A. J., Kendall, A. C. andYoung, A. T. 1988. Nitrate nutrition and temperature effectson wheat: a synthesis of plant growth and nitrogen uptake inrelation to metabolic and physiological processes.—J.exp. Bot. 39: 329-343. Growth of spring wheat was measured in cool (13°C day/10°Cnight) or warm (23°C/18°C) temperatures, combined withlarge and small amounts of nitrate fertilizer. The rate of growthof dry matter was less at cool temperatures but total growthover the same period of development was slightly greater inthe cool than in the warm. Main-shoot and tiller leaves grewslower and, despite growing for a longer period, were shorterin the cool than in the warm. They had greater fresh and drymass and content of starch and fructosans per unit area. Coolconditions increased root dry mass, root to shoot ratio andnitrogen content in dry matter. Additional nitrate increasedleaf area of main shoots slightly but of tillers greatly; itincreased leaf and tiller dry matter and total plant dry mass.Additional nitrate decreased the proportion of dry matter inroots and in stems and the N content of dry matter in all plantparts. Regulation of growth by temperature, nitrate supply andthe rôle of photosynthesis and nitrogen uptake, is consideredin relation to the mechanisms of incorporation of carbon andnitrogen into biochemical constituents. It is concluded thattemperature regulates the rate of protein synthesis, which determinesplant growth rate. Nitrogen flux into the plant is not directlylinked to protein synthesis so that the content of NO^–₃and of amino acids is related both to growth and to conditionsgoverning NO^–₃ uptake and its reduction. When nitrogensupply is large, growth is limited by temperature, not NO^–₃.Inadequate nitrate supply decreases protein synthesis (and thereforegrowth) more than it decreases carbon assimilation, so thatorgans such as roots and stems increase in dry matter relativeto shoots and all tissues have smaller proportions of nitrogenin dry matter. Cool conditions, although decreasing the rateof protein synthesis, increase its duration and decrease thesize of leaves, so that the content of protein per unit leafarea is greater in cool than in warm grown leaves. Consequencesof changes in the balance of N and C supply and growth ratefor dry matter distribution in plants are discussed. Key words: Wheat, nitrate nutrition, temperature