Distinct strategies of soil bacterial generalists and specialists in temperate deciduous broad-leaved forests

Abstract

Based on global biotic homogenization, habitat generalists and specialists play an important role in maintaining the stability of ecosystems. However, limited information is available about the assembly processes and co-occurrence patterns of soil bacterial habitat specialists and generalists in forest ecosystems, particularly their response mechanisms to environmental factors. In this study, high-throughput sequencing technology was used to investigate the role of the ecological assemblage processes of soil bacterial habitat specialists and generalists and their role in maintaining the stability of the symbiotic network in temperate deciduous broad-leaved forests (China). The results showed that compared with specialists, the diversity of bacterial habitat generalists was lower, but their distribution ranges and environmental niche breadth were wider. Results from the null and neutral models indicate that, compared to deterministic processes, the community assembly of habitat generalists and specialists is more strongly influenced by stochastic processes, with generalists exhibiting a higher degree of stochasticity than specialists. Network analysis results showed that habitat specialists played a greater role in maintaining the stability of the bacterial co-occurrence network than the generalists. In addition, bacterial habitat specialists were more likely to be affected by light and spatial feature vectors than generalists. These findings provide a novel perspective for understanding the assembly processes and diversity maintenance mechanisms of the forest soil bacterial community.

Importance: Limited information is available about bacterial specialists and generalists in forests. Generalists were more affected by stochastic processes than specialists. Specialists played a more important role in network stability than generalists. Light and spatial vectors had stronger effects on specialists than generalists.

Keywords: co-occurrence network; community assembly process; habitat generalists; habitat specialists; niche breadth; soil bacteria.

Fig 1

Location and topography of the 4.8 hm² forest dynamic plot in Baiyun Mountain National Forest Park. The map was created using ArcGIS, with the basemap sourced from the official China Standard Map Service, under map review number GS(2019)1822.

Fig 2

Spatial distribution and species composition of overall taxa, specialists, generalists, and neutral taxa in Baiyun National Forest Park. (A) Distribution map of bacterial OTU species in 120 sample plots. (B) Richness index of bacterial communities. (C) Species composition of bacterial communities.

Fig 3

Ecological processes of the bacterial communities in Baiyun Mountain National Forest Park. (A) Assessment of the influence of stochastic and deterministic processes on soil bacterial community assembly based on a null model. The inner circle represents the contribution of stochastic and deterministic processes to community construction. The outer ring represents the detailed ecological processes assigned to stochastic and deterministic processes. (B) Neutral model applied to assess the effects of random dispersal on the soil bacteria. Rsqr indicates the goodness-of-fit to the neutral model. Nm indicates the metacommunity size times immigration. m indicates the estimated migration rate. The solid blue lines indicate the best fit to the neutral model, and dashed blue lines represent 95% confidence intervals around the model prediction. (C) Comparison of the mean niche breadth of four bacterial taxa. The Kruskal-Wallis test at P < 0.05. (D) C-score metric based on null models. The values of observed C-score (C-scoreobs) > simulated C-score (C-scoresim) indicate non-random co-occurrence patterns. Standardized effect sizes <−0 and >0 represent aggregation and segregation, respectively.

Fig 4

Co-occurring network colored by modularity class for soil bacteria in Baiyun Mountain National Nature Reserve. (A) The co-occurrence patterns among OTUs revealed by network analysis. The red lines show positive correlations between nodes, and the green lines show negative relationships. Each node represents different OTUs, and the colors of the nodes indicate different modules. Modules 1–6 display different colors. A group of OTUs in one module means that these OTUs have more interactions among themselves and fewer associations with other modules. (B) Topological properties of the co-occurrence network of soil bacterial communities. (C) Relative abundance of specialists, neutral species, and generalists (OTUs) in the main modules.

Fig 5

PLS-PM showing the direct and indirect effects of different factors on bacteria richness. (A) PLS‐PM was used to examine the linkages among light, PCNM, plant, topography, and overall species richness. The blue line indicates positive correlation, while the red line indicates negative correlation. The arrow color and width indicate the strength of the relationship. Numbers on the lines out of the PLS-PM were the “weight” contributions. (B) The positive and negative effects of PCNM, topography, light, and vegetation on bacterial richness. (C) Direct and indirect effects of environmental factors on generalists, neutral species, and specialist richness.

Fig 6

Conceptual map showing the environmental breadth, co-occurrence pattern, and stochastic processes in the assembly of soil bacterial habitat generalists and specialists in the mountain forest ecosystem.