Abstract:
- Overgrazing-induced
grassland degradation has become a severe ecological problem
worldwide. The diversity and composition of soil microbial communities
are responsive to grazing disturbance. Yet, our understanding is
limited with respect to the effects of grazing intensity on bacterial
and fungal communities, especially in plant rhizosphere.
- Using a long-term (15 years) grazing experiment, we evaluated the
richness and composition of microbial communities in both rhizosphere
and non-rhizosphere regions, under light, moderate, and heavy
intensities of grazing, in a semiarid grassland. We also examined the
relative roles of grazing-induced changes in some abiotic and biotic
factors in affecting the richness and composition of microbial
communities.
- Our results showed that the responses of soil bacteria to grazing
intensity differed greatly between rhizosphere and non-rhizosphere,
and so did soil fungi.
Specifically,
the bacterial richness decreased markedly under moderate and heavy
grazing in rhizosphere soil, whereas little impact on the fungal
richness was observed. For microbial composition, with the increase in
grazing intensity, an increase in dissimilarity among bacterial
communities was observed, and this trend also held true for the fungal
communities. Hierarchical partitioning analyses indicated that the
bacterial composition in rhizosphere was primarily driven by root
nitrogen and soil nitrogen concentrations while that in
non-rhizosphere by soil available phosphorus. In addition, soil
available phosphorus played an important role in affecting the fungal
composition in both rhizosphere and non-rhizosphere regions.
- Synthesis :
This
study
provides
direct experimental evidence that the richness and composition of
microbial communities were severely altered by heavy grazing in a
semiarid grassland. Thus, to restore the grazing-induced, degraded
grasslands, we should pay more attention to the conservation of soil
microbe in addition to vegetation recovery.
KEYWORDS:bacterial
diversity,
bacterial composition, fungal diversity, fungal composition, grassland
degradation, grazing intensity, non-rhizosphere, rhizosphere