3.1. Soil properties and bacterial community composition changed
with grassland degeneration
Soil nutrient contents were different among the fields in the two
sampled grasslands (Table S1) . The contents of organic matter
(OM; 32.31–4.44 g/kg in G1 and 20.11– 3.04 g/kg in G2), TN; 1.79–0.22
g/kg in G1 and 1.10–0.19 g/kg in G2, TP; 0.46–0.22 g/kg in G1 and
0.46–0.22 g/kg in G2) decreased with an increase in level of
degradation. The highly deserted regions had the lowest OM (2.13 g/kg in
G1 and 5.02 g/kg at G2), TN (0.14 g/kg in G1 and 0.30 g/kg in G2) and TP
(0.18 g/kg in G1 and 0.28 g/kg in G2) contents. In addition, as the
degree of degradation increased, soil moisture content decreased; soil
pH did not exhibit any variation.
Bacterial richness (3526–2930 in G1 and 3709–3021 in G2) and Shannon
index (9.61–8.97 in G1 and 9.72–8.36 for G2) decreased with an
increase in level of degradation; furthermore, bacterial communities in
the deserted regions had the lowest levels of alpha diversity(Table S2, p < 0.05) . Bacterial community
composition varied significantly among regions with different degrees of
degradation. Phylum Proteobacteria was the most dominant phylum in the
communities in degraded grasslands (Figure 1A and 1C) . In
addition, the relative abundances of phyla Bacteroidetes and Firmicutes
increased with an increase in the level of degradation, and had
significantly negative correlations with soil nutrient concentrations
(OM, TN, and TP); however, the relative abundances of other major phyla
decreased with the reduction of soil nutrient concentrations in the
course of grassland degradation (Figure 1) . In addition,
PERMNOVA analysis results showed significant variation in bacterial
community composition among the regions with different levels of
degradation (Table S3, P < 0.05 ). Bray-Curtis
dissimilarity among the communities was positively correlated with OM (r
= 0.398 in G1 and 0.545 in G2), TN (r = 0.388 in G1 and 0.584 in G2), TP
(r = 0.460 in G1 and 0.482 in G2), and TK (r = 0.342 in G1 and 0.431 in
G2) contents (Figure S2, P < 0.05) , indicating
that the soil nutrient significantly influenced bacterial community
composition in the degraded grassland environments.