Effects of environment and DBH on individual methylation level
Spatial variable, edaphic variables, topographic variables and DBH can
explain over 40% of various methylation rate variations in recovering
stands but less than 30% in native stands (Fig. 2a–g). Their
contribution models were different in two populations. Contribution of
soil factors (including alone and jointly with spatial factors and
topography) to total methylation rate variation in two stands declined
slowly, by 28.4% and 23.2% in recovering and native stands,
respectively (Fig. 2d, 2g). However, the contribution of spatial factors
changed greatly in different stands. Pure contribution and joint
contribution of spatial factors to total methylation rate variation were
21.8% and 20.1% in recovering stands, but declined to 6.2% and
15.3%, respectively, in native stands. Contribution of topography to
methylation increased from 3.2% in recovering stands to 13% in native
stands.
For special edaphic factors, in recovering stands, most edaphic factors
provided various degrees of contribution to full-methylation level
variation (Fig. 2b), but only soil bulk density (BD), total
nitrogen
(TN), total phosphorus (TP), available phosphorus (AP) and elevation
showed significant correlation with the variation of hemi-methylation
levels (Fig. 2c). In native stands, the edaphic contribution to
full-methylation level variation was mainly provided by total
potassium
(TK), TP, BD and elevation (Fig. 2e), and only TK and elevation had
significant correlation with the level of hemi-methylation variation
(Fig. 2f).
DBH did not have independent contribution to methylation rate in either
recovering or native stands (Fig. 2b–g). However, in native stands,
together with soil, topography and spatial factors affected 8.3% of the
full-methylation rate variation, which was over one-third of all
full-methylation variation interpreted by all four variables (Fig. 2e).
Multiple regressions on distance matrices analysis (MRM) showed that DBH
had a negative correlation with the hemi-methylation rate and positive
correlation with the full-methylation rate (Fig. 3a). DBH also showed a
significant inverse relationship with individual relative growth rates
(Fig. 3b).