ABSTRACTThis work evaluated the dynamic changes of phyllosphere microbiota and chemical parameters at various growth stages ofPennisetum giganteumand their effects on the bacterial community, cooccurrence networks, and functional properties during anaerobic fermentation.P. giganteumwas collected at two growth stages (early vegetative stage [PA]and late vegetative stage [PB]) and was naturally fermented (NPAand NPB) for 1, 3, 7, 15, 30, and 60 days, respectively. At each time point, NPAor NPBwas randomly sampled for the analysis of chemical composition, fermentation parameter, and microbial number. In addition, the fresh, 3-day, and 60-day NPAand NPBwere subjected to high-throughput sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional prediction analyses. Growth stage obviously affected the phyllosphere microbiota and chemical parameters ofP. giganteum. After 60 days of fermentation, NPBhad a higher lactic acid concentration and ratio of lactic acid to acetic acid but a lower pH value and ammonia nitrogen concentration than NPA.WeissellaandEnterobacterwere dominant in 3-day NPAandWeissellawas dominant in 3-day NPB, whileLactobacilluswas the most abundant genus in both 60-day NPAand NPB. The complexity of bacterial cooccurrence networks in the phyllosphere decreased withP. giganteumgrowth. The ensiling process further decreased the complexity of bacterial networks, with the simplest bacterial correlation structures in NPB. There were great differences in the KEGG functional profiles of PAand PB. Ensiling promoted the metabolism of lipid, cofactors, vitamins, energy, and amino acids but suppressed the metabolism of carbohydrates and nucleotides. Storage time had a greater influence than growth stage on bacterial community diversity, cooccurrence networks, and functional profiles ofP. giganteumsilage. Differences in bacterial diversity and functionality ofP. giganteumsilage caused by growth stage appear to be offset by long-term storage.IMPORTANCEThe phyllosphere microbiota consists of various and complex microbes, including bacteria with crucial relevance to the quality and safety of fermented food and feed. It initially derives from soil and becomes specific to its host after interaction with plants and climate. Bacteria associated with the phyllosphere are highly abundant and diverse, but we know little about their succession. Here, the phyllospheric microbiota structure was analyzed within the growth ofP. giganteum. We also evaluated the effects of phyllosphere microbiota and chemical parameter changes on the anaerobic fermentation ofP. giganteum. We observed remarkable differences in bacterial diversity, cooccurrence, and functionality ofP. giganteumat various growth stages and storage times. The obtained results are important for understanding the fermentation mechanism and may contribute to high-efficient production without additional cost.