Effects of phosphorus and water supply on yield, transpirational water-use efficiency, and carbon isotope discrimination of pearl millet

Several studies have identified low soil P and water availability as major constraints to pearl millet [Pennisetum glaucum (L.) R. Br.] production in semi-arid West Africa. To evaluate the effects of phosphate and water supply on yield, transpirational water-use efficiency (WUE T ), and carbon-isotope discrimination (Δ), two varieties of pearl millet were cultivated in pots in a glasshouse at the ICRISAT Sahelian Centre, near Niamey, Niger. Phosphate and water supply had significant effects on yield, WUE T , and Δ. Compared with the control plants, which had adequate water and P availability, yield was reduced 34% by low water supply and 48% by low P supply. Under high P-supply, water stress increased WUE T by approximately 37%. Under low P-supply, no effect of water supply on WUE T was observed. Water stress increased Δ by approximately 0.6‰ for low P plants, and 0.9‰ for high P plants. Added P increased Δ by 0.3 to 0.4‰. WUE T and Δ did not differ significantly between varieties. Differences in Δ between green and necrotic leaves were found within both P treatments under low water supply. We attribute changes in A to changes in the ratio of external to internal concentration of CO 2 , (p i /p a ), leakage rates of CO 2 out of bundle-sheath cells, respiration rates, or chemical composition of the plant material.