Figure 1. Patterns of root-derived C accumulation related to (a) % ECM
tree dominance (by basal area) of the plot and (b) root production. Each
point represents one plot, with distinct sites depicted with different
shaped points. Sites include Harvard Forest (HF), Lilly-Dickey Woods
(LDW), Smithsonian Conservation Biology Institute (SCBI), Smithsonian
Environmental Research Center (SERC), Tyson Research Center (TRC), and
Wabikon Lake Forest (WLF). There is a weak negative relationship between
root-derived C accumulation and plot % ECM (R2 = 0.09, P = 0.013) but
no relationship between root-derived C accumulation and root production
at a given plot. Significant linear regression shown with shaded 95%
confidence interval.
Figure 2. (a) Root-derived C accumulation and (b) root production
related to plot mycorrhizal type. Bars represent means (with standard
error bars shown) for the AM-dominated (red) and ECM-dominated (blue)
end-member plots at each site. Sites include Harvard Forest (HF),
Lilly-Dickey Woods (LDW), Smithsonian Conservation Biology Institute
(SCBI), Smithsonian Environmental Research Center (SERC), Tyson Research
Center (TRC), and Wabikon Lake Forest (WLF). Insets show AM vs. ECM
cross-site means, with * indicating significant difference between
mycorrhizal types for root-derived C accumulation (P = 0.016).
Mycorrhizal type, but not site or the interaction between mycorrhizal
type and site, significantly predicted root-derived C accumulation
(panel a; P = 0.014). Mycorrhizal type and site significantly
predicted root production (panel b; P = 0.04 and P
< 0.001, respectively), while the interaction between
mycorrhizal type and site was marginally significant (P = 0.09 ).
There were no significant pairwise differences between mycorrhizal types
for any site in either panel a or b.
Figure 3. Ratio of annual root-derived C accumulation to annual
aboveground litter mass C at the plot level for the AM (red) and ECM
(blue) end-member plots at each site. Sites include Harvard Forest (HF),
Lilly-Dickey Woods (LDW), Smithsonian Conservation Biology Institute
(SCBI), Smithsonian Environmental Research Center (SERC), Tyson Research
Center (TRC), and Wabikon Lake Forest (WLF). The 1:1 line is shown as a
dashed grey line for reference. Bars represent plot-level means (with
standard error bars shown) for each mycorrhizal type at each site. Site
and mycorrhizal type (but not the interaction between the two)
significantly predicted annual root-derived C accumulation: litter mass
C (P = 0.003).
Figure 4. Mean root-derived MAOM-C (mg C/ g bulk soil) for the three
AM-dominated (red) and three ECM-dominated (blue) end-member plots at
three sites with standard error bars (n = 3 for each group). Mycorrhizal
type (P = 0.04) significantly predicted plot-level root-derived MAOM-C,
and the inset shows cross-site differences in AM vs. ECM mean
root-derived MAOM-C across all sites. * Indicates significant
differences between mycorrhizal types (P < 0.05). Sites
include Harvard Forest (HF), Lilly-Dickey Woods (LD), and Smithsonian
Environmental Research Center (SERC).