(3)
where, X i and Yi denote
the measured and fitted δ values of the soil, respectively, andN is the number of available data.
The structural equation model is a multivariate statistical technique
that has emerged as a synthesis of path analysis, factor analysis, and
maximum likelihood analysis. It can partition direct and indirect
effects and estimate the strengths of these multiple effects found in
natural ecosystems. The structural equation model was constructed based
on the significances of the linear regressions between the formation
efficiency of mineral-protected SOM and all the available mineralogical
properties and the compositional properties of litter and microbial-
residues in SOM as well as microbial communities, and the significances
of selected parameters in stepwise regression. The fit of the final
structural equation model was evaluated usingχ 2 and P tests (P >
0.05 of chi-squared test indicated overall fit of the data with the
model). The structural equation model analysis was conducted using AMOS
21.0 software (Amos Development Corporation, Chicago, IL, USA).
Principal component analysis of functional C groups expressed as
relative abundance of the whole C spectrum or functional microbial
groups expressed as the relative abundance of whole phospholipid fatty
acid profiles was conducted to determine the effects of the litter and
clay mineral types. The principal component analysis was performed using
SPSS 21.0 software.