Nano-zeolite-coupled biochar-based phosphate fertilizer suppresses the priming effect and promotes soil carbon stability in subtropical bamboo plantations

The application of conventional chemical fertilizers to agricultural soils often boosts crop productivity at the cost of increased soil CO 2 emissions. Climate-smart fertilizers are urgently needed to reduce the negative impacts of fertilizers on global CO 2 emissions. Here, we investigated how a nano-zeolite-coupled biochar-based phosphate fertilizer (NanoBP) regulated the priming effect of soil organic carbon (SOC) mineralization and SOC stability in intensively managed Moso bamboo soils, compared to conventional (CP) and biochar-based phosphate- (BP) fertilizers. Our 56-day incubation experiment shows that compared with CP and BP, NanoBP reversed the positive priming effect to negative one although it increased microbial biomass carbon. NanoBP also (1) reduced hydrolase activities, down-regulated the expression of SOC-degrading genes, and enhanced oxidative metabolism relative to the control; and (2) selectively preserved aromatic carbon fraction and shifted microbial communities toward carbon-conserving taxa. These gene-level microbial responses and selective preservation appeared to be driven by the slow release of phosphorus from NanoBP, pH buffering, and improved microhabitat conditions, which collectively alleviated microbial nutrient stress and reduced SOC mineralization. Our findings highlight that NanoBP offers a promising pathway to achieve nutrient–carbon co-optimization in phosphorus-limited subtropical soils. • Novel nanozeolite-coupled biochar-based P fertilizer (NanoBP) was evaluated. • NanoBP suppressed the mineralization of soil organic C by reducing the priming effect. • NanoBP shifted microbial metabolism toward C conservation by reducing enzyme activity. • NanoBP selectively preserved stable C fractions and enhanced C retention.