Statistical analyses
All data met the assumption of normality and homogeneity of variance,
and were analyzed by using SPSS 21.0 (IBM, Chicago, IL, USA).
General linear model - univariate analysis was performed to assess the
effect of target species, soil nutrition condition, and plantation
condition on the biomass and root: shoot ratio, with all factors as
fixed factors. In addition, Duncan’s post hoc analysis was conducted to
evaluate the differences of the mean value among these treatments.
General linear model - univariate analysis was used to estimate how
target species, soil nutrition condition, and neighbor species
influenced the intensity and importance of competition, with these
factors as fixed factors. Moreover, the magnitude of effects
(ω 2) of individual factor or the interaction of
two or three factors were calculated by dividing each variance component
to the total response variable (Graham et al. 2001). In addition, the
directionality of the NImpA was assessed using
one-sample t test, where a value > 0 indicates a
significant facilitation effect of the neighbor on the target species,
suggesting the trend of co-existence. While a value < 0
indicates a significant inhibition effect, suggesting the trend of
competitive exclusion. Furthermore, we estimated the difference ofNImpA on the same target species between high and
low nutrition treatments by independent sample t test.
In order to analyze the change of competitive hierarchy, the effects of
target species, soil nutrition and their interaction on the competition
intensity were analyzed for each neighbor species by general linear
model - univariate analysis, with target species and soil N condition as
fixed factors; and Duncan’s post hoc analysis was conducted to evaluate
the differences of the mean value among these four treatments. The
significant interaction between target species and soil nutrition
condition would suggest the competition change between S. grandisand S. krylovii .
The effect of target species, plantation condition on the
nutrition-addition effect was estimated by general linear model -
univariate analysis, with target species and plantation condition as
fixed factors. When significant interaction effect of target species and
plantation condition was found, a simple-effect analysis was used to
evaluate the differences among levels of one factor under a certain
condition of another factor. Moreover, the difference of the
nutrition-addition with zero was assessed using one-sample ttest.