On the controls of root lifespan: assessing the role of soluble phenolics

Aims: In addition to multiple above- and belowground abiotic factors, root herbivory can be an important determinant of root lifespan. In this study, we investigated the relationship between fine-root soluble phenolic content, a putative measure of chemical defense against herbivory, and explicit factors that have previously been related to fine-root lifespan. We hypothesized that fine-root soluble phenolic content would be positively related to factors previously shown to be correlated with increased root lifespan. Methods: In a common garden, utilizing nine temperate trees species, we examined the relationship between fine-root soluble phenolic content and fine-root branching order, diameter, rooting depth, localized nitrogen availability, and tree growth rate. Results: Consistent with our hypothesis, fine-root soluble phenolic content significantly increased with increasing branching order (P < 0.001). However, phenolic content significantly decreased with increasing localized N enrichment (P = 0.002), despite previous work indicating increased lifespan in N-enriched patches. We found no other significant relationships between fine-root soluble phenolic content and any of the other factors investigated. Conclusions: While this study provides detailed information about sources of variation in soluble phenolic content in roots, we were unable to find general utility in using a Folin-Denis based soluble-phenolic assay to increase our understanding of the factors associated with fine-root lifespan.