Direct measurement of roots in soil for single and mixed species using a quantitative DNA-based method

Molecular techniques present a new opportunity to study roots and their interactions in soil. Extraction and quantification of species-specific DNA directly from soil allows direct identification of roots in mixed swards reducing the need for labour-intensive methods to recover and identify individual roots. DNA was extracted directly from up to 0.5 kg of soil and the presence of individual species quantified using species-specific probes with quantitative real-time PCR. A range of plant and soil factors influenced the DNA content measured in roots and it was necessary to account for these influences when converting DNA amount to root mass. The utility of the method for quantitative root studies was demonstrated in an experiment to investigate the effect of lime on root growth of acid-soil resistant and sensitive perennial grasses grown together in an aluminium-toxic soil. The root mass of an acid-soil resistant species was unaffected by lime application, whereas that of an acid-soil sensitive species was restricted by soil acidity. Molecular techniques present a promising tool for quantification of root mass directly in soil and have applications for field studies involving mixed species of plants.