Dark Respiration of Winter Wheat Crops in Relation to Temperature and Simulated Photosynthesis

Abstract

The dark respiration of shoots (measured between March and anthesis in mid-June) and of ears (measured between anthesis and maturity at end of July) of winter wheat crops, grown in 1982 and 1985 under different nitrogen application and irrigation conditions, was determined in the field. The respiration rate of 126 averages of four samples was measured hourly for a 12–14-h dark period including the night. Respiration (expressed per unit dry mass) generally declined through the season for both shoots and ears. The average rate of respiration obtained on the same night was greater for fertilized and irrigated crops, compared with unfertilized and droughted crops. The relationship between the measured respiration and photosynthesis, simulated using a modified version of the model developed by Spitters (1986), was analysed. This revealed that: (a) Shoot respiration was less well correlated with photosynthesis from the day preceding measurement than with the average of the photosynthesis from the two days preceding measurement. (b) The constants relating shoot respiration to total crop photosynthesis per unit crop mass and ear respiration to total crop photosynthesis per unit ear mass had similar values. This suggests that all growth respiration takes place in the ears at the end of the season. (c) Crop growth respiration consumes about 35% of assimilate before anthesis, and that growth respiration of the ear consumes about 40% of assimilate at the end of the season. (d) No significant effect of treatment on the relationship between respiration and photosynthesis was detected, suggesting that the observed effect of treatment on respiration is due entirely to differences in photosynthesis.