Kinetic Parameters of Phosphorus Uptake as a Function of Cationic Metal Supply in Cotton

Phosphorus (P) availability is currently a limiting factor for agricultural production, especially in tropical soils, and its interaction with cationic micronutrients can significantly affect physiological efficiency and nutrient uptake by plants. Therefore, this study aimed to evaluate the uptake kinetic parameters described by the Michaelis-Menten model (Vmax, Km, and Cmin) for P as a function of the supply of Cu, Fe, Mn, and Zn, as well as the kinetic parameters of Cu, Fe, Mn, and Zn as a function of P supply in cotton (Gossypium hirsutum L.). The experiment was conducted in a greenhouse at the experimental unit of CENA, in Piracicaba, São Paulo, Brazil, using individual pots. Phosphorus concentration and accumulation were reduced only under Fe and Zn deficiency, with reductions of up to 60% in the shoots and 85% in the roots. Zn deficiency caused a drastic reduction in P uptake capacity, with Vmax decreasing from 590 to 50.85 µmol g^-1 h^-1 (approximately a 12-fold reduction), accompanied by an increase in Cmin (from 269 to 1508 µmol L^-1). In terms of micronutrient kinetics, P omission reduced plant growth and affected only Fe and Zn uptake. For Fe, Km increased from 12.82 to 27.31 µmol L^-1 and Cmin from 1.03 to 20.51 µmol L^-1. For Zn, and Vmax decreased from 0.16 to 0.02 µmol g^-1 h^-1 (approximately 8-fold), while Cmin increased from 0.08 to 1.56 µmol L^-1. These results demonstrate a strong interaction between P, Fe, and Zn, highlighting their regulatory roles in nutrient uptake and providing mechanistic insights into plant nutritional efficiency.