A method for obtaining the relationship between the amount of DNA and the fine root weight from mixtures of fine roots and soil particles

Abstract

Fine root biomass can be estimated from the quantity of DNA of a target plant extracted from fine root samples using regression analysis. However, the application of this method to fine root samples mixed with soil particles (mixed samples) is difficult due to the high DNA adsorption capacity of some clay minerals. Our aim in this study was to clarify the enhancement level of the DNA extraction efficiency of an improved method, and to obtain a regression line between the amount of DNA and the root biomass from a mixed sample with similar reliability as for fine roots alone (pure root sample). We examined the amount of DNA extracted from a mixture of Zea mays L. fine roots and highly adsorbent Kanuma soil using various concentrations of a skim milk solution, which acts as an adsorption competitor for the soil particles during the DNA extraction process. The amount of DNA of Zea mays extracted from the mixed sample using 0% skim milk was lower than from the pure root sample. However, the amount of DNA extracted from the mixed sample increased with increasing concentrations of skim milk, reaching the same level as for the pure root samples and resulting in a regression line that was similar to the pure root samples. Optimal DNA extraction levels were obtained with the addition of 20 µL of a 20% skim milk solution to 30 mg of a mixed sample. We also discuss the applicability of this method to other plant species and soil types.