Root recovery and elemental composition in a perennial grass as affected by soaking conditions

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.