Afforestation on degraded lands is an effective measure to control desertification and soil erosion, but these functions are often constrained by soil nitrogen (N) availability. Moreover, soil N availability usually shifts along plantation development, yet we have a limited understanding of factors driving this shift. Here, we examined dynamics of soil N mineralization and nitrification rates along plantation development, and explored mechanisms behind these dynamics from the perspective of N-cycling microbes. We measured needle litter quality, N-hydrolyzing enzyme activity, biomass and community composition of soil microbes (phospholipid fatty acid analysis) and ammonia oxidizers (real-time quantitative PCR and high-throughput sequencing), and net N mineralization and nitrification rates along a chronosequence of Pinus sylvestris var. mongolica stands with six age classes ranging from 15- to 61-year-old in the Three-North region of China. Results showed that stand development increased net N mineralization rate by 54%, nitrate-N concentration by 106%, and nitrate-N:ammonium-N ratio from 1.09 to 2.63. Gram-positive:gram-negative bacterial ratio and beta-N-acetylglucosaminidase activity initially increased and subsequently decreased along stand development with the highest values in 40-year-old stands, while fungal:bacterial ratio showed the opposite pattern with the lowest value in 40-year-old stands. These shifts in soil microbial properties were associated with age-related changes in needle litter C:N ratio and soil pH. Net N mineralization rate was positively related to beta-N-acetylglucosaminidase activities, but not to soil microbial biomass and community composition. Net nitrification rate was negatively correlated with ammonia-oxidizing archaeal abundances and positively with ammonia-oxidizing bacterial abundances. Collectively, our results indicate that soil N availability increases and N cycling accelerates with plantation growth, and suggest that microbial N recycling driven by beta-N-acetylglucosaminidase is tightly related to soil N dynamics along stand development.