2.7 Statistical analysis
The statistical analyses were performed by SPSS 18.0 for Windows (SPSS
Inc., Chicago, IL, USA). Differences in soil chemical properties, and
relative abundances and
α-diversity
indices, were determined between treatment means using a one-way
analysis of variance (ANOVA), and Duncan’s test was performed for
multiple comparisons. A two-way ANOVA was employed to evaluate the
interaction effects of soil depth and
plantation
age on relative abundances and α-diversity
indices.
Correlation analyses were followed using the Pearson correlation method.
Microbial community structure and diversity was quantified based on
results from
T-RFLP.
Non-metric multidimensional scaling (NMDS) and tests of Analysis of
Similarity (ANOSIM) were used to determine differences in
CO2 and N2 fixation bacteria composition
among plantation age (Clarke & Green, 1988), and the r values
associated to the NMDS were calculated using ANOSIM based on 999
permutations. NMDS and ANOSIM were computed based on the Bray–Curtis
distance using the ‘vegan’ package in R. Redundancy analysis (RDA) was
carried out to determine the relationship between soil property
parameters
and
CO2 and N2 fixation bacteria composition
using Canoco 4.5 for Windows. The statistical significance was defined
at the 5% level unless otherwise stated. All results were reported as
the means standard errors (SE) for the three replications.