Rooting for Success: The Role of Microorganisms in Promoting Growth and Resilience in Black Alder Seedlings

Polycyclic aromatic hydrocarbons (PAHs) pose a global environmental risk, impacting human health. Enhancing phytoremediation with microbial-plant interactions could help mitigate these pollutants. However, tree responses to PAHs are unclear, necessitating controlled studies before field experiments. This study examined how PAH-degrading microbes affect black alder (Alnus glutinosa L.) seedlings grown hydroponically, hypothesizing that specific microbes improve growth and stress tolerance. Two half-sib families (41-65-7 K, 13-99-1 K) were inoculated with Rhodotorula sphaerocarpa (R.s.), Pseudomonas putida (P.p.), and Sphingobium yanoikuyae (S.y.). Results showed family-dependent and microbe-specific effects, with family 41-65-7 K showing enhanced shoot growth (threefold increase by R.s.) and higher carotenoid levels. Antioxidant enzyme activities varied: R.s. elevated superoxide dismutase activity by 4.8-fold in 13-99-1 K, while catalase activity increased but decreased in 41-65-7 K. Principal component analysis revealed distinct phytochemical clustering based on microbial treatment, highlighting genotype-specific modulations. Each microorganism had unique plant growth-promoting traits, with P.p. producing the most phytohormone and S.y. fixing nitrogen. These findings support targeted microbial inoculation for effective remediation of PAH-contaminated environments.