Gas exchange and nutrition patterns during the life cycle of an artificial wheat crop

Abstract

The growth, mineral and shoot and root CO2 exchange of wheat plants (Triticum aestivum L. cv. Courtot) cultivated in growth chambers have been studied during the complete life cycle. The life cycle could be divided into 4 periods according to the patterns of CO2 exchange: exponential increase, linear increase, stabilization and decline of photosynthesis. These patterns are analysed in relation to light interception, tillering, competition between plants and ageing of the leaves, all of which constitute successive limiting factors. Root metabolism seemed to be subordinated to the demand of the shoot for minerals. Ion uptake from the nutrient solution was particularly pronounced in young plants, which were higher in minerals and nitrogen than older ones. The ratios of K and P uptake varied with plant age, and the charge balance in ion exchange was equlibrated by H uptake. Rhythmic patterns appeared in all exchanges and varied with plant age. The highest amplitude of rhythm was found in root respiration. After taking the losses due to respiration and photorespiration into account, the maximum rate of photosynthesis approached the theoretical value calculated from the light energy absorbed.