Influence of rising atmospheric C02 concentrations and temperature on growth, yield and grain quality of cereal crops

Influence of rising atmospheric C02 concentrations and temperature on growth, yield and grain quality of cereal crops

A possible scenario for the end of the 21st century is that the atmospheric C02 concentration will be in the range of 510-760 uL L-I and that the mean global temperature will be 1.5-4.5C higher. Further, there maybe greater incidences of extreme climatic events, which together with the C02 and temperature changes will influence development, growth and grain yield of cereals such as rice and wheat. For these C3 plants, the driving force for the growth response to elevated CO2 is higher leaf C02 assimilation rates (A). However, theresponse of A to C02 depends on temperature with maximum absolute increases occuring at temperatures which do not cause flower abortion, while negligible increases are observed at low temperatures. At high temperatures, where A is reduced because of partial inactivation of photosynthetic enzymes, the increase in A due to C02 enrichment is still observed. Other factors, such as changes in shoot water relations or hormone concentrations, may influence growth at elevated CO2 concentrations. Wheat and rice development is accelerated by high temperature and consequently grain yield is reduced because there is less time for radiation to be intercepted during the vegetative phase. Although high C02 also accelerates development in rice and, to a lesser extent in wheat, the extra carbohydrate produced by increases in A results in at least a 40% increase in grain yield at temperatures which do not cause flower abortion. This is due mainly to increased tiller numbers rather than increases in the number or weight of individual grains. However, the yield enhancement due to high C02 will not necessarily compensate for decreases in yield caused by accelerated development at high temperatures. As predicted by the response of A to high C02, the relative increase in yield, due to rising C02 concentrations, is smaller at lower temperatures. Elevated atmospheric CO, may improve the tolerance of plants to heat-induced drought stress by facilitating the maintenance of cell volume and photosynthetic function in the leaves. Increased carbohydrate storage in the stems may also be an advantage during grain filling if the flag leaves senesce prematurely. However, it is unlikely that the effect of very high temperatures on flower abortion will be ameliorated by high CO2. For bread making, the quality of flour produced from grain developed at high temperatures is poorer. High CO2 may also have an effect through a reduction in the protein content of wheat grain. For rice, the amylose content of the grain, a major determinant of cooking quality is increased under elevated CO2.

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