Significance levels: ***: p < 0.001; **: p< 0.01; *: p < 0.05.
Since forest age and soil depth also contributed to building microbial
community composition, partial Mantel tests were performed to estimate
the independent contribution of each environmental factor after removing
the effects of forest age and soil depth. Partial Mantel test results
showed that FI (r = 0.11, p < 0.01) and HIX (r = 0.23,p < 0.01) were environmental factors significantly
associated with bacterial community composition (Table 2) and soil SOC
(r = 0.11, p < 0.05) but their effects were apparently
much smaller; FI was the key to influence the distribution of fungal
communities (r = 0.14, p < 0.05) and other
environmental factors were not significantly influenced.
Linear regression analyses showed that the diversity of bacteria and
fungi all increased significantly as DOM quantity increased. Diversity
of fungi all declined as FI increased (r = 0.32, p = 0.058; Fig.
S3e) and bacteria increased as HIX increased (r = 0.71, p< 0.05; Fig. S3c). This indicated that fungal communities were
more diverse when DOM was more plant-dominated in origin than those
microbial sources dominated and increasing humification of DOM
significantly enhanced bacteria diversity.
4. Discussion