Effects of temperature and nitrogen supply on post-floral growth of wheat : measurements and simulations

Warmth accelerates the rate of grain growth in wheat, but the temperature coefficient expressed as Q ₁₀ decreases gradually between 10 and 25°C. The rate of protein deposition responds more to temperature than the total grain dry matter accumulation rate. Warmth shortens the post-floral phase in cereals. The relation can be approximated by a direct log-linear relationship between temperature and duration, or by a heat sum above a minimum temperature. The proportion of the final amount of nitrogen in the shoot taken up by the roots after anthesis declines upon increase in the concentration of nitrogen in shoot dry matter at anthesis. The component shoot organs contribute to the total amount of nitrogen relocated from the shoot to the grains in amounts proportional to the amounts of nitrogen present in these organs at anthesis. Instantaneous effects of change in temperature on the apparent photosynthesis rate per plant were small. Differences in apparent photosynthesis per plant, which developed in time between temperature treatments or nitrogen treatments, were primarily attributable to the impact of these factors on the rate of leaf senescence. Measured respiration rates were compared with theoretically expected rates. There was agreement between calculated and observed growth respiration of grains. Measured respiration rates of non-grain organs (respiration related with maintenance and transport mainly) were considerably greater than theoretically expected rates, especially in roots. A dynamic simulation model is presented that describes and interrelates post-floral gross photosynthesis, respiration, grain growth, uptake and redistribution of nitrogen, and leaf senescence. According to model predictions final grain yield in the field (for Dutch climate and crop management) decreases by 30-40 g.m ^-2 per degree centigrade rise in temperature throughout grain filling (other input data fixed). This adverse effect of temperature can be offset by a concomitant increase in daily radiation of 130-180 J.cm ^-2 (PhAR). Yield differences between crops that differ in amount of shoot nitrogen at anthesis only are predicted to be 15-20%.