Nutrient Concentrations of Roots Vary More with Site Than Soil Depth.

Roots are very difficult to sample for tissue analysis, especially at depth.  We analyzed patterns of nutrient concentrations in roots collected from quantitative soil pits at the Bartlett Experimental Forest, which allowed us to study roots at depths not accessible in stony forest soils using traditional coring methods.  We also compared roots measured with cores at a variety of sites contrasting in soil chemistry, including Sleepers River, VT; Cone Pond, NH; Hubbard Brook, NH; and Huntington Forest, NY, where two contrasting sites were studied.  We analyzed concentrations of nitrogen, phosphorus, calcium, magnesium and potassium as a function of soil depth and root diameter. 

Variation in root chemistry with depth within the six sites at Bartlett was not significant, which means that sampling can be restricted to roots near the surface, which are easier to collect.  The exception was K, for which fine roots increased in concentration with depth, and coarse roots decreased.  Root diameter, as expected, was a significant predictor of root concentrations.  At Bartlett, where we compared fine roots (0-1 mm) with coarse roots (5-10 and 10-20 mm), N and Mg were higher in concentration in the finer roots but Ca was lower.  Site differences were striking.  Concentrations of Ca, Mg, and K in roots from a base-rich site at Sleepers River were more than twice as high as at the other sites, consistent with variations in soil chemistry.  Differences between the two sites at Huntington confirmed this pattern.  The results from this study confirm the importance of sampling roots by site, but suggest that sampling roots at depth for soil chemistry can be avoided.