Introduction
Soil microorganisms participate in almost all biogeochemical cycles and
are extremely important for maintaining soil ecosystem functions
(Bardgett & van der Putten 2014; Wagg et al. 2019; Zhou et
al. 2020), whilst a large body of literature has documented that soil
ecosystem functions can be threatened by land use change possibly due to
loss of microbial biodiversity under land disturbance (Cardinaleet al. 2012; Allan et al. 2015). For instance, previous
studies have found that high microbial diversity is of stability via
recruitment from the indigenous taxa pools, and hence land use change
may lead to alpha diversity in decoupling of plant and microbial
community (Allan et al. 2015; Zhou et al. 2020). While
land use change, as a key component of global change, has occurred
worldwide, particularly, recent land use change has induced dramatic
alterations in vegetation type and microbial attributes (Cardinaleet al. 2012; Cheng et al. 2013; Allan et al. 2015),
and thus concurrently can affect belowground biodiversity and ecosystem
functioning. However, the relationship between soil microbial
biodiversity and ecosystem functions in response to land use change
remains largely uncertain due to soil microorganisms’ huge diversity
with the taxa ranging from hundreds to thousands per gram of soil
(Torsvik & Øvreås 2002; Bardgett & van der Putten 2014).
Numerous studies conducted with plants and microbes support a consensus
view that the relationship between microbial biodiversity and ecosystem
functioning (i.e. BEF relationship) is the fundamental in addressing
global environment changes (Tilman et al. 2014; Isbell et
al. 2015). Some studies have generated that ecosystem functions
decrease with the loss of biodiversity in the experiments and
observation (Tilman et al. 2014; Meyer et al. 2018), as
well as in the meta-analyses (Cardinale et al. 2012;
Delgado-Baquerizo et al. 2016b; Zhou et al. 2020).
Generally, the linear BEF relationship suggests that each species has a
proportional effect on ecosystem function with no functional redundancy
(Delgado-Baquerizo et al. 2016a; Trivedi et al. 2019a).
Whereas, the logarithmic BEF relationship indicates that a small loss of
biodiversity has a minimal or none impact on ecosystem due to the
functional redundant (Louca et al. 2016; Trivedi et al.2019a).
Soil ecosystem functions such as the board (widely dispreads living
microbe, e.g. decomposition) and specialized (i.e. ammoxidation) levels
are critical for ecosystem energy gaining and nitrogen supplying
processes (Bender et al. 2016; Manning et al. 2018; Zhouet al. 2020). And determining the BEF relationship at the broad
and specialized level is of pivotal significance to estimate the impact
of diversity losses induced by land use change on ecosystem functioning
such as soil carbon sequestration or decomposition (Allan et al.2015; Delgado-Baquerizo et al. 2016a; van der Plas 2019). It has
been argued that these two ecosystem functions are known as relatively
independent microorganisms’ communities (Srivastava & Vellend 2005;
Delgado-Baquerizo et al. 2016a). For microbial keystone taxa
usually drive community richness and function irrespective of their
abundance (Banerjee et al. 2018), consequently, changes in
keystone taxa can affect soil ecosystem function and reconstruct the BEF
relationship. A big challenge is how to explicitly identify the
relationship of the board and specialized functions with microorganisms
in response to land use change. Although most of these interactions of
microbes living network cannot directly observe, the network-based
analytical approach is a useful tool to infer the microbial interaction
and keystone species of the complex network (Deng et al. 2012;
Weiss et al. 2016). Thus, the construction of a co-occurrence
network enables our disentangling the BEF relationship under land use
change.
In this study, we identified the BEF relationship under land use change
in the Danjiangkou Reservoir area in central China. After the project of
Middle Route of China’s South-to-North Water transfer Project was
constructed, large areas of cropland have been converted to shrubland
and woodland since 1980s (Cheng et al. 2013). Our previous
studies have demonstrated afforested lands enhanced soil quality, and
microbial activities (Cheng et al. 2013; Feng et al.2018). Therefore, the variations in soil microbial communities and
diversity are expected across over 30 years of land use change in our
study site, which is useful to evaluate the relationship between
microbial diversity for both broad (i.e. microbial basal respiration)
and specialized function (i.e nitrification rate). Here, we hypothesize
that: (i) the pattern of BEF relationship would vary with across land
use change in the status that land use change would substantially alter
soil microbial communities; (ii) considering for environmental changes
across different land use types, the role of maintaining nitrification
rate shifts between AOA and AOB possibly due to niche differentiation.