# Dynamics and Function of Foliar Endophytic Bacterial Communities of Ammopiptanthus mongolicus Across Different Leaf Growth Stages

## TL;DR

This study explores how bacterial communities in the leaves of a desert shrub change as the leaves age, revealing patterns in diversity and function.

## Contribution

The paper provides new insights into the dynamics of foliar endophytic bacteria in a xerophytic relict species across leaf growth stages.

## Key findings

- Bacterial community diversity and evenness increased from young to mature leaves but declined at the Old1 stage.
- Old1 and Old2 stages showed distinct bacterial communities compared to Young and Mature stages.
- Functional predictions indicated shifts in chemoheterotrophy and correlations between nutrients and leaf stages.

## Abstract

Ammopiptanthus mongolicus is a relict species from the ancient Mediterranean of the Tertiary period and the only strong xerophytic evergreen broad-leaved shrub in the central Asian desert. Foliar endophytic and epiphytic bacteria jointly form phyllosphere microorganisms that influence plant health. This study investigated the dynamic changes in foliar endophytic bacterial communities across four leaf growth stages (Young, Mature, Old1, and Old2). Illumina 16S region (V5–V7) amplicon sequencing was used to analyze community composition, function, construction process, and environmental driving factors. The Old1 and Old2 stages were clearly separated from the Young and Mature stages, which demonstrated closer clustering. Community diversity and evenness first increased from the Young to Mature stages, declined at the Old1 stage, and finally reached maximum values at the Old2 stage; richness increased gradually. Total amplicon sequence variant (ASV) numbers, stage-specific ASVs, and their proportion increased with leaf development, whereas the proportion of shared ASVs between adjacent, interval, and all stages decreased. Dominant genera were Rhodococcus (Young), unclassified_f__Comamonadaceae (Mature), Rhodococcus (Old1), and Bacillus (Old2). Co-occurrence networks became progressively simpler, with reduced inter-node and positive connectivity. Functional predictions revealed that chemoheterotrophy and aerobic chemoheterotrophy decreased initially and then increased, with the lowest values at Old1. N, C/P, N/P, and SOD reached maximum at the Old2 stage. P was maximum at the Mature stage. P, C/P, and N/P were significantly positively correlated with the Young stage, N with the Mature stage, and SOD with the Old2 stage (p < 0.05). These findings enhance understanding of the diversity, composition, function, and plant–endophyte relationships in xerophytic relict species, particularly evergreen desert shrubs.