Root recovery and elemental composition in a perennial grass as affected by soaking conditions
Thivierge, M.N., Royer, I., Halde, C., Chantigny, M.H., Bélanger, G., Lachance, C., Lavergne, S. (2021). Root recovery and elemental composition in a perennial grass as affected by soaking conditions. Agronomy Journal, [online] 113(5), 3952-3967. http://dx.doi.org/10.1002/agj2.20821
Plain language summary
In order to study the traits of plant roots sampled in the field, such as their mass, length, or elemental composition, it is essential to separate roots from soil without inducing root damage. Fibrous roots of perennial grasses are particularly challenging to separate from the soil. To facilitate root washing, soil samples from the field can be soaked in an aqueous solution. To this end, we compared five soaking solutions [sodium bicarbonate, sodium chloride, disodium ethylenediamine tetraacetic acid (disodium EDTA), distilled water, and sodium hexametaphosphate] and three soaking durations (15 min, 2 h, and 16 h) for their effectiveness in facilitating the washing of timothy roots collected from a loamy soil. Soaking duration did not affect the mass and length of roots recovered after washing. However, the roots soaked the longest (16 h) had the least ash and were therefore the least contaminated with soil (137 g ash per kg of roots, compared to 146 g/kg on average for the shorter durations). We can thus recommend soaking the samples 16 h before washing roots. The sodium bicarbonate solution allowed recovering the larger root biomass (0.118 g per sample), while the average of the other four soaking solutions was 0.101 g per sample. Sodium hexametaphosphate removed the most residual soil from the roots, leading to the lowest ash concentrations, but left a phosphorus residue on the roots. Distilled water did not alter the integrity of the root cells, unlike several other soaking solutions. In conclusion, it is important to consider the specific objectives of each study, as no single soaking solution both optimizes root recovery (mass and length) and minimizes residual soil adhering to it.
Roots of perennial grasses, with their fibrous architecture, are difficult to separate from the surrounding soil. We assessed the effect of five soaking solutions (sodium bicarbonate, sodium chloride, disodium ethylenediamine tetraacetic acid [disodium EDTA], distilled water, and sodium hexametaphosphate) and three soaking durations (15 min, 2 h, and 16 h) on root recovery and root elemental composition, with and without a mathematical correction for residual soil adhering to roots. Roots were collected by soil coring in a timothy (Phleum pratense L.) sward on a loam soil. After soaking, roots were washed, digitized, and analyzed for elemental composition. Soaking duration did not affect root mass and length, but the 16-h duration resulted in the lowest ash concentration (136.7 vs. 146.4 g kg–1 dry matter [DM] on average across shorter durations), indicating a lower contamination by soil. The greatest root recovery was obtained with sodium bicarbonate (0.118 vs. 0.101 g DM core–1 on average across other solutions). Sodium hexametaphosphate led to the lowest root ash and element concentrations but left a P residue on the roots. Distilled water did not impair root cell integrity and led to a similar root recovery as sodium chloride, disodium EDTA, and sodium hexametaphosphate. A mathematical correction improved the estimates of (a) root mass for all soaking solutions and (b) root elemental composition for elements with higher concentrations in soils than in roots. Soaking solutions should be chosen as a function of the study objectives because of the trade-off between root recovery and contamination by adhering soil.