Rare soil microbial taxa regulate the negative effects of land degradation drivers on soil organic matter decomposition

1. Land degradation drivers, including loss in vegetation and
eutrophication, are expected to impact soil biodiversity and functions in
drylands world-wide. Soils contain both common and rare microbial taxa
that drive multiple soil functions. Yet, little is known about how these
microbial taxa influence the impacts of land degradation drivers on
ecosystem functions. Obtaining this information is essential to determine
whether rare taxa need to be protected, or if protecting only common taxa
would be enough to sustain and protect ecosystem functions and services.
2. Here, we conducted an experiment to investigate the effects of
N-enrichment and vegetation loss (plant removal), which are two major land
degradation drivers in semi-arid grasslands, on the diversities of common
and rare soil bacterial and fungal taxa and soil function [soil organic
matter (SOM) decomposition] in a long-term experiment. 3. Six years after
N-enrichment and vegetation loss, we found that N-enrichment decreased the
alpha diversities of common and rare soil bacteria and rare soil fungi,
while vegetation loss only decreased the alpha diversity of rare soil
fungi. Both N-enrichment and vegetation loss altered the community
composition of common and rare bacteria and fungi, except for the lack of
response of common soil fungi to the vegetation loss. Moreover, both
structural equation modelling and variation partitioning analyses show
that land degradation drivers reduce SOM decomposition, and these were
also indirectly associated with changes in the diversity of rare microbial
taxa, especially that of bacteria. 4. Synthesis and applications.
Collectively, this work shows that land degradation can have negative
impacts on soil biodiversity and functions, and the rare microbial taxa
indirectly regulate the impacts of land degradation on ecosystem
functioning. These results indicate that the rare microbial taxa can be
used as one of the ecological indicators for identifying land degradation
in the semi-arid grasslands. These findings are essential to understand
the future impacts of desertification and land degradation on rare
microbial taxa–function relationships in global drylands.