The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Abstract

Winter wheat (Triticum aestivum L. cv. Hereward) was grown in the field inside polyethylene-covered tunnels at a range of temperatures at either 380 or 684 μmol mol−1 CO2. Serial harvests were taken from anthesis until harvest maturity. Grain yield was reduced by warmer temperatures, but increased by CO2 enrichment at all temperatures. During grain-filling, individual grain dry weight was a linear function of time from anthesis until mass maturity (attainment of maximum grain dry weight) within each plot. The rate of progress to mass maturity (the reciprocal of time to mass maturity) was a positive linear function of mean temperature, but was not affected by CO2 concentration. The rate of increase in grain dry weight per ear was 2.0 mg d−1 greater per 1 °C rise, and was 8.0 mg d−1 greater at 684 compared with 380 μmol mol−1 CO2 at a given temperature. The rate of increase in harvest index was 1.0% d−1 in most plots at 380 μmol mol−1 CO2 and in open field plots, compared with 1.18% d−1 in all plots at 684 μmol mol−1 CO2. Thus, the increased rate of grain growth observed at an elevated CO2 concentration could be attributed partly to a change in the partitioning of assimilates to the grain. In contrast, the primary effect of warmer temperatures was to shorten the duration of grain-filling. The rate of grain growth at a given temperature and the rate of increase in harvest index were only independent of the number of grains per ear above a critical grain number of 23–24 grains per ear (˜20 000 grains m−2).