Forest ecology has a significant impact on soil total organic carbon (TOC) pool because of alterations in substrate induced changes in soil enzymatic activity and microbial diversity. We investigated impacts of poplar (Populus deltoides) chronosequence on organic C pool and its metabolic potential to predict changes induced by altered microbial diversity in semiarid ecosystems of Indian lower Himalayas. The present study integrates metagenomics to quantitatively appraise the bacterial communities in response to enzymatic activities and build-up of organic C in soils under poplar chronosequence (6-years, cycle-1; 12-years, cycle-2 and 18-years, cycle-3) established in lower Himalayas. Chronosequence of poplar-based agroforestry significantly (p<0.05) increased the TOC pool by similar to 27.2-43.3%, while C build-up was manifested by a significant increase in soil related glomalin protein (TG) by similar to 17.2-44.4% after completion of cycle-3, compared with the shorter chronosequence. Amongst different soil enzymatic activity, CM Case activity varied between 37.5 and 47.5 g glucose g(-1) soil hr(-1); Fpase activity between 7.11 and 9.55 mu g glucose g(-1) soil hr(-1) and dehydrogenase (DHA) between 27.6 and 35.1 mu g TPF g(-1) soil hr(-1) in soils under different poplar-based chronosequence. Amongst the different chronosequence, soil protein varied between 349.6 and 475.0 mu g protein g(-1) soil, while fungal biomass between 395.7 and 527.8 mu g n-acetyl glucosamine g(-1) soil in soils under different poplar-based chronosequence. Total organic C, fungal biomass and microbial protein exhibited a significant relationship with xylanase, exocellulase, and beta-glucosidase activity in soils. Poplar chronosequence (cycle-2 and cycle-3) exhibited a consistent linear increase in alpha-diversity of microbial taxonomy and microbial diversity at phylum, genus and species level. The microbial taxonomical structure and composition revealed that Actinobacteria, Chloroflexi, Planctomycetes, Firmicutes and Proteobacteria were largely affected by poplar chronosequence due to increased eubacterial community diversity. These results significantly improved our understanding of soil C cycling in soils under poplar based agroforestry in semiarid ecosystems in context of climate change by focusing on soil microbial C metabolic potentials and biological properties. These results suggest that poplar chronosequence are the main regulatory factors of bacterial diversity and microbial C metabolism processes, and can potentially play a central role in mediating the stability of C pool. This study contributed to a better understanding of the response of soil microbial community and C metabolic potentials. Therefore, implementing policies for promotion and adoption of poplar-based agroforestry practices can contribute to climate change mitigation efforts by fostering soil C sequestration and resilience in agricultural landscapes.