Characterizing root nitrogen uptake of wheat to simulate soil nitrogen dynamics.

Background and aims: Michaelis-Menten (MM) kinetics and a physical-mathematical (PM) model are the popular approaches to describe root N uptake (RNU). This study aimed to examine RNU and compare the two model approaches. Methods: A hydroponic experiment (Exp.1) investigated the effects of root length, root N mass, transpiration, plant age and solution N concentration on RNU of wheat ( Triticum aestivum L. cv. Jingdong 8). The two models were applied to simulate the RNU and soil N dynamics in a soil-wheat system (Exp.2), and the results were compared to the measured data. Results: Under the hydroponic conditions, RNU was better correlated with root N mass and transpiration than root length. The influences of solution N concentration on RNU rate per root length (MM1) and RNU rate per root N mass (MM2) were described well with MM kinetics. The kinetic parameters for MM1 changed with plant age but the parameters for MM2 were not age dependant. The description of RNU with the PM model was also independent of plant age, and was more reliable when the RNU factor decreased as a power function with the solution N concentration (PM2) than an assumed constant (PM1). In Exp.2, the root mean squared errors between the simulated and measured soil solution N concentration and the relative errors between the simulated and measured N uptake mass for MM kinetics were much larger than those for the PM model. Conclusions: Both the MM and PM models successfully described RNU under the hydroponic conditions, but the PM model (especially PM2) was more reliable than the MM model in the soil-wheat system. [ABSTRACT FROM AUTHOR]