Spatiotemporal variation of nitrate uptake kinetics within the maize ( Zea mays L.) root system is associated with greater nitrate uptake and interactions with architectural phenes

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Nitrate uptake kinetics varied among maize root classes, and simulations demonstrated that increasing the maximum uptake rate, I _max, of all roots could increase plant growth by as much as 26%.

Abstract

Increasing maize nitrogen acquisition efficiency is a major goal for the 21st century. Nitrate uptake kinetics (NUK) are defined by I _max and K _m, which denote the maximum uptake rate and the affinity of transporters, respectively. Because NUK have been studied predominantly at the molecular and whole-root system levels, little is known about the functional importance of NUK variation within root systems. A novel method was created to measure NUK of root segments that demonstrated variation in NUK among root classes (seminal, lateral, crown, and brace). I _max varied among root class, plant age, and nitrate deprivation combinations, but was most affected by plant age, which increased I _max, and nitrate deprivation time, which decreased I _max. K _m was greatest for crown roots. The functional–structural simulation SimRoot was used for sensitivity analysis of plant growth to root segment I _max and K _m, as well as to test interactions of I _max with root system architectural phenes. Simulated plant growth was more sensitive to I _max than K _m, and reached an asymptote near the maximum I _max observed in the empirical studies. Increasing the I _max of lateral roots had the largest effect on shoot growth. Additive effects of I _max and architectural phenes on nitrate uptake were observed. Empirically, only lateral root tips aged 20 d operated at the maximum I _max, and simulations demonstrated that increasing all seminal and lateral classes to this maximum rate could increase plant growth by as much as 26%. Therefore, optimizing I _max for all maize root classes merits attention as a promising breeding goal.