# Differential assembly and functional roles of bacterial communities in coniferous and mixed conifer-broadleaf forest soils

## TL;DR

This study compares bacterial communities in coniferous and mixed forests, showing how different soil conditions and forest types influence microbial diversity and function.

## Contribution

The study reveals distinct assembly mechanisms and functional roles of abundant and rare bacterial taxa in different forest types.

## Key findings

- Abundant and rare bacterial communities differ significantly between coniferous and mixed conifer-broadleaf forests.
- Soil pH and organic matter influence abundant communities, while available phosphorus and potassium affect rare communities.
- Mixed forests support bacteria involved in carbohydrate degradation and nitrogen fixation, while coniferous forests favor stress-adapted microbes.

## Abstract

Forest soils harbor a diverse array of bacteria that play a crucial role in
nutrient cycling. However, the differential effects of coniferous versus
mixed conifer-broadleaf forests on the distribution of both abundant and
rare bacterial taxa remain poorly understood. In this study, we integrated
16S rRNA gene amplicon sequencing with metagenomic shotgun sequencing to
conduct a comparative analysis of soil bacterial communities in a conifer
plantation and an adjacent mixed conifer-broadleaf forest, specifically
examining their community structure, assembly mechanisms, co-occurrence
networks, and functional potential. Both abundant and rare taxa showed
significant differences in community composition between the two forest
types. Soil pH and organic matter content significantly influenced the total
and abundant bacterial communities, while available phosphorus and potassium
were key determinants of rare community composition. Co-occurrence network
analysis revealed that abundant communities formed highly clustered,
simplified networks, contrasting with more fragmented and keystone-rich
networks in rare communities. Null model analyses indicated that community
assembly was largely driven by stochastic processes, with ecological drift
accounting for about 80% of the variation in total and rare communities, and
dispersal limitation explaining nearly 72% of the variation in abundant
communities. Functional predictions indicated that bacterial communities in
mixed forests were enriched in pathways linked to glycosylation,
carbohydrate degradation, and nitrogen fixation, while coniferous forests
favored pathways related to autophagy, signaling, and stress responses. This
study highlights the complementary roles of abundant and rare bacterial taxa
in forest soil ecosystems and underscores the importance of preserving mixed
forests to sustain microbial functional diversity.

Forest soils host a complex web of common and rare bacteria that quietly
regulate nutrient cycles. By comparing pure conifer stands with mixed
conifer-broadleaf forests, we found that abundant species underpin
essential functions while rarer microbes fill specialized niches.
Acidity and nutrients strongly influence which bacteria thrive; mixed
stands favored microbes that break down carbohydrates and fix nitrogen,
whereas conifer soils supported organisms adapted to stress and
nutrient-poor conditions. These findings emphasize the importance of
preserving diverse forest ecosystems for soil health, carbon storage,
and effective forest management strategies in climate change
adaptation.