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Soil compaction and nitrate capture

While lateral roots comprise the bulk of root length, axial roots function as a scaffold determining the distribution of these laterals.

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Although root penetration of strong soils has been intensively studied at the scale of individual root axes, interactions between soil physical properties and soil foraging by whole plants are less clear. Christopher Strock and colleagues investigated how variation in the penetration ability of distinct root classes and bulk density profiles common to real-world soils affect soil foraging strategies.

A plant’s ability to penetrate soil varies with the soil compaction. When pores in the soil are poorly connected, and there are few gaps in the soil, it’s difficult for a root to push soil particles out of the way. When roots are impeded, they reach into a smaller volume and have access to fewer nutrients in the earth. This, in turn, reduces the productivity of agriculture. So it would be useful to understand how roots interact with soils. Strock and colleagues say in their article there has been research on this, but they take it further.

“Although many of the processes surrounding the penetration of individual root axes are well researched, the broader interactions between soil structure, metabolic costs of soil exploration and plant fitness are less clear. Presently, empirical data relating soil structure and root length density are sparse due to the complex and laborious nature of the field-based measurements required to adequately assess these interactions.”

Many simulated root systems, with their roots hanging down like the tendrils of purple jellyfish.
Root architecture and length per soil layer of 40-day-old maize root systems with variable penetration ability of axial and lateral root classes. Image: Strock et al. 2022.

The team used a new module for the plant model OpenSimRoot that accounts for interactions between soil physical properties, root growth and metabolic costs, allowing for the simulation of more realistic growth scenarios. They used this model to examine how different root classes varied in their ability to penetrate soils of differing hardness.

Strock and colleagues found that soils with plow pans and bulk density gradients affected overall size, distribution and carbon costs of the root system. Soils with high bulk density at depth impeded rooting depth and reduced leaching of nitrate, thereby improving the coincidence of nitrogen and root length.

Strock and colleagues conclude: “While increasing penetration ability of either axial or lateral root classes produced root systems of comparable net length, improved penetration of axial roots increased allocation of root length in deeper domains, thereby amplifying N acquisition and shoot biomass. Although enhanced penetration ability of both root classes was associated with greater root system carbon costs, the benefit to plant fitness from improved soil exploration and resource capture offset these. While lateral roots comprise the bulk of root system length, axial roots function as a scaffold determining the distribution of these laterals. In soils with high soil strength and leaching, root systems with enhanced penetration ability of axial roots have greater distribution of root length at depth, thereby improving capture of mobile resources.”


Strock, C.F., Rangarajan, H., Black, C.K., Schäfer, E.D. and Lynch, J.P. (2022) “Theoretical evidence that root penetration ability interacts with soil compaction regimes to affect nitrate capture,” Annals of Botany, https://doi.org/10.1093/aob/mcab144

Alex Assiry

Alex Assiry is an editorial assistant in the Annals of Botany Office. When not working, Alex listens for the opportunity to help.

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