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.