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).

Transmitted and Absorbed Photosynthetically Active Radiation in Grain Sorghum1

“…As much as 14% of the incident PAR was absorbed by the stalks and 8% by panicles ( Table 2). The percentage absorbed by panicles is similar to that found by Muchow et al ( 1982) and Fischer et al (1976). Sorghum cultivars that have semiopen panicles absorb 13% more PAR than cultivars that have closed panicles, which were used in this study (Eastin, 1968).…”

Simulating Seed Number in Grain Sorghum from Increases in Plant Dry Weight

“…Cultivar‐dependent coefficients relate daily aboveground dry weight to seed number as: where SNO is the number of seeds per plant that can be supported by the accumulated daily aboveground dry weight, DRIWT is the daily increase in aboveground dry weight (g plant −1 ), AVSD is an empirical cultivar‐ and temperature‐dependent coefficient for relating the daily increase in aboveground dry weight to seed number, AVSNO is the weighted average seed number per plant, i is the day number starting with panicle initiation, and NND is the time interval (d) beginning 1 wk after growing point differentiation. These equations describe the relationship between increasing plant dry weight accumulation and seed number per plant in irrigated environments (Fischer et al, 1976; Wright et al, 1983) but do not address the wide range of planting dates and plant populations reported by Baker (1982) Similar relationships were used for maize ( Zea mays L.) by Kiniry and Knievel (1995) Few values of AVSD are available (Rosenthal et al, 1989). In its current form, AVSD and AVSNO are probably less sensitive to environmental conditions (like water stress) when the structures responsible for seed number are forming (Heiniger et al, 1997).…”

Timing and height of defoliation affect vegetative growth and floral development in grain sorghum

“…The trend continued in the current experiment with plants defoliated above the first ligule having more leaves, green leaf area, and dry weight at anthesis than those plants defoliated above the second ligule, and similar green leaf area and plant dry weight to the control plants. Continued defoliation in T6 increased the area of the 2 uppermost leaves on the plant and those leaves contribute significantly (45%) to canopy photosynthesis during grain filling (Fischer et al 1976).…”