Forest Disturbance Drives Changes in the Functional Traits of Soil Bacteria: A Metagenomic Study of Kauri ( <scp> <i>Agathis australis</i> </scp> ) Forest Ecosystems

ABSTRACT The native old‐growth kauri ( Agathis australis ) forests of Aotearoa New Zealand are increasingly threatened by multiple ecological disturbances, including biodiversity loss, historical deforestation and disease outbreaks. Soil microbial communities play a central role in maintaining forest ecosystem functioning and facilitating recovery following disturbance, yet their responses to disturbance in kauri forests remain poorly understood. This study investigated how soil bacterial communities respond to contrasting historical disturbance regimes across nine kauri forests. We hypothesised that greater forest disturbance intensity would be associated with reduced microbial diversity and functional capacity, with potential consequences for microbial contributions to soil ecosystem processes and forest resilience. Using shotgun metagenomics, we assessed differences in bacterial taxonomic diversity, functional gene diversity, average genome size and predicted growth rates in soils collected from forests spanning low‐to‐high disturbance intensities. The most pronounced shifts in soil bacterial communities were observed in the most intensively disturbed forest, Kaiaraara. Soil bacterial communities from Kaiaraara Forest were consistent outliers, having the lowest predicted growth rates, functional gene diversity, carbon‐degrading gene abundance and most distinct taxonomic composition. Soils from Kaiaraara Forest also had unusually low organic matter and near‐neutral pH–abiotic conditions atypical of kauri forests – which likely contributed to these differences. Predicted growth rates of soil bacterial communities remained stable across disturbance levels, declining only at the most severely disturbed forest site of Kaiaraara. Our results revealed contrasting effects of forest disturbance on taxonomic diversity versus functional capacity: bacterial taxonomic diversity was highest in the least‐ and most‐disturbed forests, while average bacterial genome size – a proxy for functional capacity – peaked in intermediately disturbed sites. Overall, our findings highlight how forest disturbance alters both the structure and function of kauri soil bacterial communities. These insights are critical for evaluating the resilience of kauri forests to future environmental pressures.