3.4 Assembly processes and phylogenetic structuring under
grassland degradation
The βNTI values of the two grasslands were mainly between -2 and +2(Figure 4A and 4B) , indicating the dominance of stochasticity
and weak environmental selection during community assembly across
different levels of grassland degradation.
According to the results of correlation analysis, Proteobacteria and
Bacteroidetes relative abundance had no significant correlation with
phylogenetic clustering; furthermore, there were no significant
correlations between environmental variables and ses.MNTD(Figure 4C and 4D, P > 0.05) . However, soil
nutrient contents were negatively correlated with ses.MNTD values in
other phyla (Figure 4C and 4D, P < 0.05) ,
indicating that soil nutrient loss decreased phylogenetic clustering in
bacterial communities. Considering the decrease in the niche overlap(Figure 3B and 3D) and the correlation between alpha diversity
and ses.MNTD of the phyla across different levels of grassland
degradation (Table 2) , the phylogenetic dispersion could have
resulted from the elimination of some close phylogenetic species with
functional redundancy.