Introduction
The impacts of biodiversity on ecosystem function are a classical and
central topic in ecology(Bardgett & van der Putten 2014).
Alpine plant and microbial
communities are models for understanding pioneer communities, and the
primary components of resilient ecosystems(Winkler et al. 2019).
Relationships between plants and
microbiota across environmental gradients could affect the ability of
ecosystems to adapt to impacts such as climate change,by driving the
maintenance biodiversity(Shen et al. 2021), community
stability(Yang et al. 2022a), and ecosystem functioning (Wardleet al. 2004). Under natural conditions, the interactions between
plant and microbial communities are
complex, as they involve several factors that interact with each other
and are subject to both biotic and abiotic influences, including
temperature and water balance conditions (Cobian et al. 2019;
Ware et al. 2021), plant
species categories and distributions
(Põlme et al. 2018; Yang et al. 2022b), and
soil element nutrients(Zhu et
al. 2022). However, most of these network studies on plant-microbiota
interactions have focused on the rhizosphere microbiotas which vary
among only one or a few distinct plant species (Toju et al. 2013;
Toju et al. 2015; Polme et al. 2018; Yao et al.2019), but it is still unclear how the traits of plant-microbial
interactions vary along the plant diversity gradient.
With regard to the biogeographical patterns of soil microbiota, studies
have been conducted on a range of scales, from global (Chu et al.2020) to regional (Yang et al. 2021a) to the elevational zones of
a single mountain (Yang et al. 2021b). These studies have noted
patterns in relation to latitude (Fuhrman et al. 2008),climate
(Yuan et al. 2021), soil characteristics(Chen et al.2021), and land use (Xue et al. 2022) for example. However, few
studies have considered the effects of plant richness and plant
productivity on microbial cooccurrence network.
In this study, we apply cooccurrence network analysis to soil microbial
communities and associated plants across an extensive area of the
Tibetan Plateau samples. Cooccurrence networks are used to detect the
possibility of specific interactions within communities (Barberánet al. 2012). This methodology empirically indicates the strength
of interactions between species both positive and negative. The strength
of these network interactions has been shown to correlate with the
ability of the soil biota to carry out biogeochemical processes, and
their resilience to environmental changes (Seaton et al. 2022).
Previous studies have shown that the plant diversity enhances soil
fungal diversity in the natural environment of the Tibetan Plateau (Yanget al. 2017), as well as the soil fungal network stability in a
diversity manipulation experiment (Shen et al. 2022). Here, we
compared 60 sites along the precipitation gradient of the Tibetan
Plateau, to qualitatively and quantitatively explore the proportions of
multiple factors on different features of the cooccurrence network
between plants and soil microbiotas. Using data from sampling carried
out as part of a wide ranging study, we analysed amplicon data of the
fungi (ITS2), bacteria (16S) and records of plant species present in
each of 60 sites.
Our main question in this study was as follows: what are the
cooccurrence relationships between plants and soil microbiota, and how
does this vary along the environmental and plant richness gradients that
are present?
We found a clear trend of decreasing richness of fungal OTUs associated
with each plant species, along a gradient of decreasing total plant
species richness. We suggest that this may reflect a decrease in
reliance on specialised relationships by both plants and fungi due to
reduced available energy in the more extreme plant species-poor
environments. By contrast, the richness of specifically associated
bacterial OTUs per plant species increased along this gradient,
suggesting that bacteria may substitute as specialists in increasingly
extreme environments associated with low plant species richness.