Plant-associated microbial source assemblages and abiotic conditions shape tissue-specific endophytic microbiomes and growth responses of Ageratina adenophora

Abstract Background Plant invasions are shaped not only by plant traits and environmental conditions but also by interactions with associated microbial communities that may influence host performance and ecological adaptation. Although invasive plants frequently encounter different plant-associated microbial sources from surrounding plant communities, how variation in these microbial sources influences microbiome assembly and plant performance under changing environmental conditions remains poorly understood. Using the globally invasive plant Ageratina adenophora as a model system, we conducted a controlled factorial experiment in growth chambers to investigate how plant-associated microbial source assemblages interact with temperature and water availability to influence endophytic microbiomes and plant growth. Results Endophytic community composition was primarily structured by plant tissue type, whereas microbial source assemblages explained additional variation, particularly in leaf-associated bacterial communities. The A. adenophora -derived microbial source treatment exhibited distinct endophytic community characteristics, including higher leaf bacterial Shannon diversity and enrichment of several discriminative taxa. Temperature and water availability were associated with tissue-specific microbial shifts, with stronger treatment-associated changes detected in root endophytic communities. The effects of microbial source assemblages on plant growth varied across abiotic conditions. Partial least squares path modeling further indicated that temperature and water availability were strongly associated with biomass variation, while root fungal community characteristics showed a potential indirect statistical association with temperature-related biomass responses. Conclusions Our findings indicate that endophytic microbiome assembly in A. adenophora is associated with interactions among tissue-specific filtering, microbial source assemblages, and abiotic environments. Rather than reflecting effects of source species number alone, variation in microbial source assemblages may influence invasive plant growth through context-dependent plant–microbe associations under changing environmental conditions.