Changes in microbiome assembly of the pioneer Andean tree Alnus acuminata in response to land degradation

Land degradation in the Andes threatens ecosystems and biodiversity. The recovery of these areas often depends on pioneer species such as Alnus acuminata , which relies on symbiotic microorganisms for nutrient acquisition and stress tolerance. Understanding how degradation affects its microbiome is crucial for effective restoration. This study investigated how a land-use trajectory involving deforestation and abandonment impacts the diversity and structure of bacterial communities associated with Alnus acuminata . Next-generation sequencing of 16S rRNA gene amplicons was used to compare bacterial communities in bulk soil, roots, and root nodules between a native forest and degraded forest in the Ecuadorian Andes. Land degradation significantly altered bulk soil bacterial diversity and community structure, with pH and carbon content identified as key environmental drivers. Degraded soils were dominated by Actinomycetota, whereas native forest soils harbored more diverse communities, including Acidobacteriota and Pseudomonadota. Root endophytic and nodule-associated communities showed reduced diversity under degradation, although not statistically significant, suggesting that these niches are buffered from environmental changes. Nevertheless, their community structures differed significantly, indicating that Alnus acuminata may actively assemble a beneficial bacterial consortia to cope with degraded conditions. Alnus acuminata appears to respond to soil degradation by recruiting a more diverse and functionally beneficial endophytic microbiome, including stress-resilient, pathogen-defending, and plant growth-promoting genera such as Micromonospora , Rahnella , Rhodanobacter , Mycobacterium , and Deinococcus . This adaptive strategy likely supports its survival and establishment in nutrient-poor, degraded environments, highlighting the critical role of plant-microbe interactions in ecosystem recovery and suggesting that harnessing these interactions could improve restoration outcomes.