Mechanistic Approach to Study Manganese Influx and Its Depletion in the Rhizosphere of Wheat and Raya

Abstract

Nutrient flux into the root is assumed to be a function of nutrient in soil solution at the root surface as described by the Michaelis–Menten equation. To study manganese (Mn) influx and its depletion in the rhizosphere of wheat and raya, a greenhouse pot experiment was conducted using a Mn‐deficient Typic Ustochrept loamy sand soil treated with 0, 50, and 100 mg Mn kg− 1 soil. In no‐Mn treatment, Mn influx of raya was 2.5 times higher than that of wheat, which resulted in 4 times more Mn uptake by raya. Root surface area of raya was 2.3 times more than that of wheat; for that reason raya root could exploit Mn from a greater volume of soil. Nutrient uptake model calculations satisfactorily predicted Mn influx in both wheat and raya and the calculated Mn influx values were close to the experimentally measured Mn influx values, which indicated that the calculated concentration profiles are accurate. Raya could decrease Mn concentration at the root surface by 25% of the initial value in no‐Mn treatment after 36 days of uptake, while this decrease in Mn concentration was only 5% in wheat. The higher Mn influx of raya was due to its capability to decrease the Mn concentration at the root surface to a lower value, thereby causing a concentration gradient and so the transport of Mn to the root surface. Sensitivity analysis showed that, under Mn deficiency conditions, the initial soil solution Mn concentration (CLi) the most important parameter controlling Mn influx in wheat and raya followed by root radius (r0), maximum net influx (Imax) and Michaelis–Menten constant (Km) in the listed order.