Sodium in soil can be a problem. On the surface of the ground, it can help form crusts. These hard barriers can be difficult for a seedling to break through. Deeper in the soil, the same qualities can make the soil hard and blocky, posing problems for young roots. In a recent study in Annals of Botany, Monia Anzooman and colleagues examine the influence of sodic soils on coleoptile length and root growth angle in wheat.
“The angle between the first pair of seminal roots (seminal root angle) has been associated with temporal and spatial acquisition efficiency of soil resources,” write Anzooman and colleagues in their paper. “For example, Nakamoto and Oyanagi (1994) demonstrated significant genotypic variation in the angular spread of wheat seminal roots and argued that deeply rooted wheat genotypes exhibit a narrower angle of seminal roots, while genotypes with a shallower root system tend to grow their seminal roots more horizontally. Thus, wheat genotypes with a narrow seminal root angle may be more likely to extend deeper in the soil, which might provide an advantage for plants growing in sodic soils. Plants with a narrower seminal root angle may also be able to produce a greater resistance force when growing, which could result in seedlings being able to exert a greater emergence force and potentially emerge through soil crusts more easily.”
The authors found that neither exchangeable sodium percentage nor bulk density in the soil had an impact on root seminal angles. The team did, however, notice an inverse relationship between the seminal root angle and the values for emergence rate. By reaching deeper into the soil for moisture, the plants may have higher turgor to push through any soil crust. This relationship is a subject that will require more study.
In contrast, the length of the coleoptile, the sheath that protects the young shoot reaching for the sun, appeared to have no significant differences between the genotypes used in the experiments. The authors do not believe that coleoptiles will help identify the wheat strains best suited to sodic soils. Instead you should look below, they conclude. “The results presented here suggest that selection for narrow seminal root angle may potentially help to identify wheat genotypes that are better adapted to sodic soils, a positive relationship being observed between emergence rate in crusted sodic soils and narrower root angle.”