<p>Nitrogen (N) is one of the limiting nutrients for plant primary productivity. However, it is unclear how trees shape both biotic and abiotic soil properties that enhance N availability in the rhizosphere at different forest ages. This study aimed to elucidate the mechanisms of ammonification, nitrification, and net N mineralization along a chronosequence from young (18-year-old) to mature (63-year-old) stands of <i>Pinus massoniana</i> in southern China. We measured the net N transformation rates, soil nutrients, and bacterial and fungal communities in the rhizosphere and bulk soils of different stand ages. We also analyzed the relationships between the functional groups of bacteria and fungi and net N transformation rates. From 18 to 63 years, the increase in rates of ammonification, nitrification, and net N mineralization varied from 1.1 to 1.7 times in rhizosphere soils, while it was 0.6 to 1.8 times in bulk soils. In addition, the difference in nitrification rates between rhizosphere and bulk soil increased to 40%. In contrast, the difference in ammonification rates decreased at the stand age of 30 and then increased with stand age. Soil labile carbon and available phosphorus content positively contributed to rhizosphere soil N transformation with stand age. Changes in the abundance of bacterial and fungal phyla and functional groups with stand age explained more than 99% of the soil N transformation rate. Chitinolysis and dung saprotroph were the main functional groups governing soil N transformation rates in the rhizosphere soil of <i>P. massoniana</i>, indicating that <i>P. massoniana</i> can affect the substrate supply of soil N by reshaping rhizosphere microorganisms and thus affect the N supply at the corresponding stand age. Stand development can alter the dynamics of soil available carbon and phosphorus, as well as the composition of microbial functional groups, which subsequently contributes to an increase in N transformation rates with stand age.</p>