h stages. On the other hand, most bacteria and metabolites showed non-linear relationships with stand age (Figures three, 7). This was mostly due to the fact competition among folks in old stands was greater than that in young stands; therefore, trees in old stands have to translocate higher quantities of nutrients owing to interspecific competition, and their bacterial communities face extra stress from secondary metabolites (Chen and Wang, 2013). The phyllosphere bacterial diversity decreased in the juvenile towards the mature stages and enhanced in the mature towards the overmature stages (Figures 1B,C). These trends predominantly reflect that self-thinning begins at the juvenile to mature stages, which increases the secondary metabolites concentration and suppresses bacterial diversity (Sun et al., 2011). The variation in phyllosphere bacterial diversity with stand age observed in the present study is consistent with variation within the soil bacterial diversity of Chinese fir plantations, which indicates that the growth status of Chinese fir could influence microhabitats and, consequently, the microbes that inhabit those microhabitats (Wang C. Q. et al., 2019). Despite the fact that the phyllosphere communities in the 4 growth stages comprised related bacterial members, distinct variations had been observed in alpha and beta diversity, which indicated that the phyllosphere bacterial composition was one of a kind at each stand age (Figure 1) (Delhaes et al., 2012). The major explanation for the shift within the bacterial neighborhood composition is nutritional modifications: net photosynthesis in conifers decreaseswith stand age (Greenwood et al., 2008; R m et al., 2012). Hence, bacterial carbon metabolism was highest in the sapling stage, along with the limited leaf location promoted antibiotic biosynthesis in the sapling stage (Figures 5F,J). The nitrogen:phosphorus ratio in the leaf frequently increases with stand age (Zhang et al., 2015, 2018; Zhou H. et al., 2016), as well as a reasonably higher degree of nitrogen nutrition decreases the bacterial nitrogen metabolism function. Most variable metabolites have been associated with metabolic and secondary metabolites biosynthesis pathways (Figure 5B). Prior study indicates that the dominant bacteria in the phyllosphere of conifer needles aren’t only comparable across stand ages, but additionally amongst areas (Rastogi et al., 2012). This similarity may possibly be EP Activator drug caused by the stability of cuticular wax HIV-1 Antagonist Storage & Stability chemicals (e.g., long-chain hydrocarbons), which provide a continual atmosphere for bacteria (Tinto et al., 2017; Wang et al., 2018). The genera Sphingomonas, Pseudomonas, Massilia, Methylobacterium, Methylocella, and Akkermansia showed higher relative abundances at all stand ages (Figure 3B). This outcome is comparable to these reported by Purahong et al. (2016) and Tl kal et al. (2016). These authors reported that the relative abundances of your genera Sphingomonas, Pseudomonas, and Massilia have been greater in juvenile and mature stands than in sapling and overmature stands. Members with the genus Methylobacterium perform numerous functions, for instance inhibition of pathogenic bacteria (Garc -Coca et al., 2020), nitrogen fixation (Sy et al., 2001), and pollutant degradation (Lu et al., 2019). Having said that, their functions when they colonize leaves and needles stay unclear. Given that phyllospheric Methylobacterium bacteria include ultraviolet Aabsorbing compounds (Yoshida et al., 2017), these bacteria may boost the resistance of leaves and needles to oxidative strain brought on by higher light inte