Studies of grain production in Sorghum bicolor (L. Moench). VII.* Contribution of plant parts to canopy photosynthesis and grain yield in field stations

Abstract

A method based on ¹⁴CO₂ uptake and carbon dioxide exchange in sorghum canopies at medium and high density populations allowed the estimation of photosynthesis by plant parts (heads, and leaves at each level of insertion) after anthesis.

The relative importance of corresponding parts did not differ between populations, nor did photosynthetic rates per unit leaf area. The latter did decline with successive leaf position down the canopy but were generally compensated by increasing area of these leaves. Averaged over the two populations, which differed little, the heads provided 14% of canopy photosynthesis, and the flag leaf and leaves 2, 3 and 4 were responsible for 21, 24, 21 and 13% respectively. Greater leaf areas per unit land area in the higher population, for each leaf position, resulted in higher total canopy photosynthesis.

Previous studies having shown that net photosynthesis after heading corresponds closely to grain yield, the relative importance of plant parts to overall net photosynthesis may be regarded as their relative contribution to grain filling. A direct estimate of their importance in this regard, based on another method, showed the head to contribute 17%, and the next four leaves 17, 25, 20 and 17%.

Factors controlling photosynthetic rates of parts are discussed, and the estimates of the importance of photosynthetic sites to grain filling are compared with those reported in previous work.

_____________________ *Part VI, Aust. J. Agric. Res., 27: 35 (1976).