1. Introduction
Microbes are ubiquitous in the Earth’s biosphere, executing essential
ecosystem functions and maintaining ecosystem
stability(Bardgett & van der Putten,
2014; Fuhrman, Cram, & Needham, 2015;
B. Gilbert & Lechowicz, 2004). The
diversity of soil microbial communities is in general positively
associated with ecosystem multifunctioning
(Bradford et al., 2014;
Delgado-Baquerizo et al., 2016;
Lefcheck et al., 2015). As a major
component of microbial communities, revealing the diversity patterns
across space and through time is of essential importance for better
understanding the underlying ecological mechanisms governing the
distribution and assembly of microbial communities. However, the tiny
size of microorganisms and immense complexity of microbial communities
make this issue more challenging than macrobial communities.
Taxa-area relationship (TAR) and distance-decay relationship (DDR) are
two typical and perhaps universal spatial scaling patterns followed by
both macrobial and microbial
communities(Green et al., 2004;
M. C. Horner-Devine, M. Lage, J. B.
Hughes, & B. J. Bohannan, 2004; Tu et
al., 2016; Zinger, Boetius, & Ramette,
2014). Of these, TAR describes the pattern of continuously increasing
species richness with increasing sampling
area(Connor & Mccoy, 1979;
Rosenzweig, 1995), whereas DDR describes
the pattern that the composition of biological communities becomes more
dissimilar with increasing geographic
distance(Nekola & White, 1999). Although
different in concept, both TAR and DDR are assumed to be the result of a
set of common processes, including environmental heterogeneity and local
community assembly processes (e.g., speciation, drift, and dispersal
limitation) across sampling area and
distance(Connor & Mccoy, 1979;
Hubbell, 2001). Specifically, higher
environmental heterogeneity is associated with more ecological niche
space and habitat types, allowing more microbial taxa to
coexist(Allouche, Kalyuzhny, Moreno-Rueda,
Pizarro, & Kadmon, 2012; Huber et al.,
2020; Yang et al., 2015). The larger
sampling area it is, the higher environmental heterogeneity and more
coexisted microbial taxa are expected, resulting in TAR patterns.
Environmental heterogeneity also contributes to DDR patterns for its
being strongly correlated with geographic
distance(Tilman, 1983). Local community
assembly processes may also result in differed community structure and
composition(Stegen et al., 2013;
X. Zhang et al., 2020). leading to TAR
and DDR patterns. However, TAR and DDR may not be directly derived from
each other, and may be subjected to influences by different ecological
factors(Zinger et al., 2014).
Microbial communities in natural ecosystems are typically composed by a
small number of abundant taxa and an extremely long tail of rare
taxa(M. D. Lynch & Neufeld, 2015;
Sogin et al., 2006). The abundant taxa
usually occupy < 20% of the total richness, but
> 80% in relative
abundance(Sogin et al., 2006). Although
low in relative abundance, recent studies suggest that the rare
microbial taxa execute nonnegligible ecosystem functions in the
environment(Q.-L. Chen et al., 2020;
Lyons & Schwartz, 2001;
Mouillot et al., 2013;
Xiong et al., 2021). Recent studies
suggested that the abundant and rare subcommunities are structured by
different community assembly mechanisms and environmental
parameters(Jiao & Lu, 2020;
Mo et al., 2018;
W. Zhang et al., 2018). However, it
remains not clear whether and how abundant and rare subcommunities
differ in the spatial scaling patterns they may follow and how such
patterns are linked to environmental heterogeneity and local community
assembly processes.
In this study, we investigated the spatial scaling patterns followed by
abundant and rare subcommunities of microbes in an ocean sediment
ecosystem, aiming to address the following ecological questions: (1) Do
abundant and rare subcommunities differ in following spatial scaling
patterns? (2) How do environmental heterogeneity and local community
assembly mechanisms respectively contribute to the spatial scaling
patterns? We expected that abundant and rare subcommunities may differ
in the spatial scaling patterns they follow, mainly due to their
different life strategies (e.g., different adaptability to environmental
conditions)(He et al., 2022;
Wan et al., 2021). Specifically, abundant
subcommunities may follow weak spatial scaling patterns, especially TAR,
as they are more broadly distributed across the sampling space. As
previously reported, abundant and rare subcommunities differ
dramatically in local community assembly
mechanisms(Jiao & Lu, 2020;
Mo et al., 2018;
W. Zhang et al., 2018). We therefore
expected strong links between local community assembly and spatial
scaling patterns. The results confirmed our expectation that spatial
scaling patterns were rarely observed for abundant subcommunities,
whereas rare subcommunities were mainly responsible for the observed
microbial spatial scaling patterns. Distinct ecological mechanisms
underlay the spatial scaling patterns followed by abundant and rare
subcommunities. The study provided novel mechanistic insights into the
spatial scaling patterns followed by different types of microbes.