Abstract
There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg−1 soil, leaf P content increased from 0.65 to 7.0 g kg−1. Both A and DM had maximal values near 51.7 mg P kg−1 soil, which corresponded to a leaf P content of 3.2 g kg−1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (gs) tripled, and mean leaf internal CO2 concentration ([CO2]i) decreased from 260 to 92 μL L−1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both KM, which is mathematically equivalent to quantum efficiency, and Vmax, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg−1, with peak values between 4 and 5 g P kg−1. Polynomial equations relating KM and Vmax, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
