PHOTOSYNTHESIS OF WHEAT UNDER FIELD CONDITIONS .2. EFFECT OF DEFOLIATION ON CARBON DIOXIDE UPTAKE OF COMMUNITY

A field assimilation chamber was used to measure the carbon dioxide uptake ofwheat plants in the field before and after defoliation or ear removal. At anthesis and10 days later only the top three leaves were effective in photosynthesis. Removal ofthe 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 anadditional 24-30%. The estimated contribution of the ears depended on the techniqueof measurement and varied from 7 to 15%. After removal of the leaf laminae andears, the stems and leaf sheaths assimilated carbon dioxide at a rate of 44% of that ofthe whole community. For defoliated plants, photosynthesis of the ears and stems increased with increasingelevation of the sun, which indicated a greater efficiency of photosynthesiswith an increased horizontal component of radiation. This was opposite to the responseof the undefoliated community. The techniques of estimating the contribution of individual organs to totalphotosynthesis of the wheat plant are discussed in relation to variability of resultsand the effects of compensation. © 1969 CSIRO. All rights reserved.