A molecular approach to quantify root community composition in a northern hardwood forest - testing effects of root species, relative abundance, and diameter

Research on root community structure is currently limited by the methodologies available. We evaluated a molecular-sequence-based approach to quantify the relative abundance of roots from different plant species in mixed samples. We extracted DNA from mixtures of roots, amplified the trnL intron by polymerase change reaction, and identified up to 60 clones from each mixture. We tested the effects of root diameter and species on sequence representation in mixtures. Species were correctly identified in our mixtures. Recovery efficiencies were low for root diameter classes >0.3 mm compared with those <0.3 mm, and species in high abundance in the mixture had relatively low recovery efficiency. American beech (Fagus grandifolia Ehrh.) was quantitatively underrepresented compared with yellow birch (Betula alle-ghaniensis Britton) and white ash (Fraxinus americana L.). Root identification by sequencing is accurate and can readily be applied to novel systems without new primer development. This technique will be attractive for documenting changes in relative abundances of species, especially as the cost of sequence-based analyses drops. However, the results of such analyses must be considered carefully, as root diameter distribution, abundances, and species can introduce quantifiable biases in the estimation of relative root abundance.