Influence of source-sink alterations on photosynthesis and nitrogen fixation in pigeon pea

Abstract

The treatment of pigeon pea (Cajanus cajan L.) designed to enhance the photosynthetic source-sink ratio (depodding) resulted in increased total and specific nodule activities by 122 and 159%, respectively. Conversely, treatments designed to reduce the photosynthetic source-sink ratio, i.e. shading and defoliation, reduced total nodule activity by 33 and 39%, respectively. Compared with control, depodding, shading and defoliation decreased shoot respiration, but root and nodule respiration was increased by these treatments. Depodding had no effect on the rate of photosynthesis but this was deshaded in defoliated and shaded plants. Interestingly, during the later growth stages, shaded plants maintained higher photosynthetic rates compared with control because of greater leaf area. No significant effect was observed on dry weight and protein content of seeds at harvest, which indicated that no advantage accrued to the plant as a result of enhanced nitrogen fixation by depodding.