Total Canopy Photosynthesis Research Articles

Leaf Photosynthetic Response to Foliar Fertilizer Applied to Corn Plants During Grain Fill1

AbstractFoliar fertilization of field crops has received renewed interest as a method of increasing seed yield by supplying additional nutrients to the leaves to delay the normal depletion of nutrients in the leaves during reproductive stages. It has been hypothesized that application of foliar fertilization may delay natural leaf senescence. We tested this by estimating leaf photosynthesis in field‐grown corn (Zea mays L.) plants using a 14CO2 uptake procedure. A small segment of the leaf material enclosed in a chamber is exposed to 14CO2 for a short time period. Leaf samples are then analyzed using standard radiotracer techniques. In 1976 and 1977 14CO2 uptake rates were measured on a number of days between silking and plant maturity in conjunction with a larger experiment relating the response of corn to foliar fertilizer application and soil moisture deficits. The experimental plants were field‐grown in a Nicollet loam soil (an Aquic Hapludoll, fineloamy, mixed, mesic).These measurements indicated that the rate of leaf photosynthesis was depressed by as much as 17% the day following foliar‐fertilizer application, but had nearly recovered by the 2nd day. A similar pattern occurred in leaf conductance. No difference in the seasonal trend of photosynthetic rate was detected between control and foliarfertilizer treatments.Photosynthetic patterns after foliar‐fertilizer application may warrant further investigation, as significant yield reductions were noted in these experiments. Because the technique used in our experiments monitors rate of photosynthesis on small, intact leaf segments, totalcanopy photosynthesis and transpiration measurements could reveal helpful information.

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

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).