Photosynthesis of wheat under field conditions. II.* Effect of defoliation on the carbon dioxide uptake of the community

Abstract

A field assimilation chamber was used to measure the carbon dioxide uptake of wheat plants in the field before and after defoliation or ear removal. At anthesis and 10 days later only the top three leaves were effective in photosynthesis. Removal of the two leaves below the flag leaf reduced photosynthesis of the community by 25–28% and further removal of the flag leaf reduced the community photosynthesis by an additional 24–30%. The estimated contribution of the ears depended on the technique of measurement and varied from 7 to 15%. After removal of the leaf laminae and ears, the stems and leaf sheaths assimilated carbon dioxide at a rate of 44% of that of the whole community.

For defoliated plants, photosynthesis of the ears and stems increased with increasing elevation of the sun, which indicated a greater efficiency of photosynthesis with an increased horizontal component of radiation. This was opposite to the response of the undefoliated community.

The techniques of estimating the contribution of individual organs to total photosynthesis of the wheat plant are discussed in relation to variability of results and the effects of compensation.

* Part I, Aust. J. Agric. Res., 1968, 19: 711.