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Age affects tree growth and development by a combination of environmental and endogenous signals,which requires highly coordinated action at the molecular,cellular,tissue,organ,and organism levels.However,the underlying mechanisms are poorly understood,particularly at a molecular level.In this paper,we investigated the transcriptomic changes of the uppermost main stems of Larix kaempferi in an entire rotation period with high-throughput RNA sequencing technology.In total,about 151 million reads were obtained from the stems of 1-,2-,5-,10-,25-and 50-year-old L.kaempferi trees.Combining these with the published Illumina sequencing reads,299,637 assembled transcripts were generated,of which 161,232 were annotated.12,927 transcripts were identified as differentially expressed genes(DEGs)by timeseries expression profiling.Function enrichment analysis of these DEGs indicated that 459 gene ontology terms in biological process category were enriched.The results showed that(1)age effects on wood formation involves genes related to many cell activities,such as cell division,cell differentiation and cell death;(2)genes related to vegetative to reproductive phase transition play negative and positive roles simultaneously during the early stage of tree growth;(3)age affects not only tree responses to hormone but also hormonal homeostasis and transport.In addition,the expression patterns of 31 transcripts were found to be correlated with tree age trend.Altogether,the comparative transcriptomic analysis reported here demonstrated the molecular aspects of age effects on L.Kaempferi tree growth and development at a pathway level.Study initiated on the biological processes involved in forest tree aging should improve our understanding of tree growth and optimizing timber rotation period in the future.