Figure 4. Mean Sassafras albidum root structural carbon δ¹³C values from higher-order dissected roots.

Trees were labeled and sampled in 2008. Control roots were sampled from unlabeled control trees and labeled roots were sampled from trees labeled with 99% ¹³CO₂. Late wood refers to the innermost portion of the dissected roots (see Figure 2). Early wood refers to the root tissue immediately surrounding the late wood. Secondary cortex refers to the outermost portion of the root surrounding the early wood. Note that less negative values indicate greater isotopic enrichment. Error bars denote standard error. Different lower case letters denote significant differences at P≤0.05 using a one tailed T-test between dissected root tissue from unlabeled control trees and labeled trees.