Quantifying the contribution of mass flow to nitrogen acquisition by an individual plant root

• Published in: The New phytologist 2018-04, Vol.218 (1), p.119-130
• Main Authors: McMurtrie, Ross E., Näsholm, Torgny
• Format: Article
• Language: English
• Subjects: Biosphere; Botanik; Botany; Capacity; Computer simulation; diffusion; Dye dispersion; Immobilization; Mass; Mass flow; Mineral nutrients; Moisture content; Nitrogen; nitrogen (N) immobilization; nitrogen uptake model; Nutrition; Plant nutrition; Plant roots; Probability theory; Rhizosphere; rhizosphere processes; Roots; root‐nitrogen uptake; root–microbe competition; Soil; Soil microorganisms; Soil water; soil‐nitrogen transport; Transport; Transport processes; Uptake; Water uptake
• ISSN: 0028-646X; 1469-8137; 1469-8137
• DOI: 10.1111/nph.14927

The classic model of nitrogen (N) flux into roots is as a Michaelis–Menten (MM) function of soil-N concentration at root surfaces. Furthermore, soil-N transport processes that determine soil-N concentration at root surfaces are seen as a bottleneck for plant nutrition. Yet, neither the MM relationship nor soil-N transport mechanisms are represented in current terrestrial biosphere models. Processes governing N supply to roots – diffusion, mass flow, N immobilization by soil microbes – are incorporated in a model of root-N uptake. We highlight a seldom considered interaction between these processes: nutrient traverses the rhizosphere more quickly in the presence of mass flow, reducing the probability of its immobilization before reaching the root surface. Root-N uptake is sensitive to the rate of mass flow for widely spaced roots with high N uptake capacity, but not for closely spaced roots or roots with low uptake capacity. The results point to a benefit of root switching from high- to low-affinity N transport systems in the presence of mass flow. Simulations indicate a strong impact of soil water uptake on N delivery to widely spaced roots through transpirationally driven mass flow. Furthermore, a given rate of N uptake per unit soil volume may be achieved by lower root biomass in the presence of mass flow.