How Number, Diameter and Length of Lateral Roots Influence Nutrient Uptake: A Simulation Study with OpenSimRoot

Lateral roots are generally considered to be of great importance for nutrient uptake, but their morphological characteristics are often not measured. Rather experimental research focuses on total root length as easily obtained by winrhizo. Length can however be obtained through longer or increased number of lateral roots. Furthermore, not length, but surface area might be closer related to nutrient uptake, and surface area can also be increased through increasing diameters.

Using a maize root architectural model, constructed with OpenSimRoot, we show that, although uptake of N, P and K does correlate positively with root system size, there is significant variation in uptake that depends on lateral root morphological traits. The simulation studies suggest that nutrient uptake is most sensitive to increased growth rates and least sensitive to increase diameter, with increased branching density intermittent. However, it may be assumed that greater length requires greater diameter, possibly to have greater penetration strength or greater transport capacity. Such linkage between growth rate and root diameter have been promoted by Pagès et al, supported by empirical measurements. This constrained, e.g. longer roots have to be thicker, can causes lateral root branching density to become the more efficient way for increasing of P and K, but not N. Furthermore, increased diameter-length results in decreasing specific root length and thereby might be unfavorable from a perspective of investment strategy.

We conclude that lateral root morphology influences the functioning of the root system. The plant thereby faces tradeoffs between length, diameter and number of roots. We strongly suggest that root research will focus more strongly on lateral root morphology, and how number, length and diameter relate to 1) each other, 2) local soil conditions and 3) nutrient status of the plant.