Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer

Abstract

Carbon dioxide production in the dark by ears and by the rest of the shoot of winter wheat grown in the field was measured in 2 years during grain growth. The respiration rate per g d. wt of the ears was increased by nitrogen fertilizer. Ears of the semi-dwarf varieties Maris Fundin and Hobbit respired more slowly than ears of Maris Huntsman and Cappelle-Desprez. Respiration rates of the rest of the shoot were unaffected by nitrogen or variety. The amount of carbohydrate required to provide the CO2 respired during the whole period of grain growth varied from 163 to 443 g m−2, or 42 to 76 per cent of the dry weight of the grain. More than half the CO2 lost was respired by the ear. The addition of 180 kg N ha−1, which increased grain yield by 78 per cent in 1975, almost trebled the amount of CO2 lost by the ears. The semi-dwarf varieties lost less CO2 from ears and shoots than did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the 14C contents of shoots sampled immediately after a 30 s exposure to 14CO2 and at maturity. When 14C was supplied 10 days after anthesis, the loss by maturity amounted to 16–28 per cent of that initially absorbed by flag leaves and 40 per cent of that absorbed by the leaf below the flag leaf. Most of the loss occurred in the first day. The loss of 14C by maturity was significantly increased by nitrogen fertilizer in 1975.