Net photosynthetic rate in peanut (Arachis hypogaea L.):: Influence of leaf position, time of day, and reproductive-sink

Net photosynthetic rate (P-N) was studied in field-grown peanut cv. GG 2 in relation to leaf position, time of day, reproductive-sink, and phenophase. In general, P-N remained higher in the upper leaves (first from top to the fourth) than in the lower leaves (fifth to eighth). The mean P-N of the leaves situated upper and the leaves lower in the canopy increased from the morning, reached a maximum during noon hours, and decreased thereafter. Between 09:00 to 10:00 h, P-N, stomatal conductance (g(s)), and transpiration rate (E) in the upper leaves were higher than in the lower leaves, but between 12:00 and 13:00 h, these activities increased significantly in the lower leaves. Highest PN was found during pod-development phase. Removal of flowers, and hence of active reproductive-sink, decreased plant height and number of leaves, and initiated accumulation of photosynthates in the leaves. The P-N per unit leaf area in plants with reproductive-sink (WRS) was similar to those without reproductive-sink (WORS). However, leaf area of WORS plants decreased significantly, mainly due to the reduction in number of leaves. No feed-back inhibition of P-N (per unit leaf area) was found despite accumulation of photosynthates in the leaves as a result of removal of the active reproductive-sink.