Abstract: Microbially induced calcium carbonate precipitation (MICP) is a key process in biologically driven carbon sequestration and plays a significant role in regulating the global carbon cycle. However, as global reactive nitrogen background levels continue to rise, the mechanisms by which anthropogenic nitrogen pollution interferes with MICP remain poorly understood. Nitrate and urea represent the most representative forms of inorganic and organic nitrogen in natural environments, respectively. Bacillus pumilus is renowned for its exceptional environmental stress tolerance, while Priestia megaterium is characterized by high mineralization efficiency. With these two bacteria as model organisms, this study conducted gradient concentration cultivation experiments with nitrate and urea, combined with carbonic anhydrase activity assays, X-ray diffraction, and scanning electron microscopy mineralogical characterization, to evaluate the effects of different nitrogen source inputs on bacterial growth, mineralization rate, and crystal polymorph of mineralization products. The results indicate that: (1) both nitrate and urea addition inhibited bacterial growth and carbonic anhydrase activity, with the inhibitory effect of nitrate intensifying with increasing concentration; (2) The two strains exhibited distinct nitrogen-source metabolic preferences: in B. pumilus, the mean mineralization rate under urea addition (63.52%) was higher than that under the nitrate treatment (52.81%), whereas the opposite pattern was observed in P. megaterium (70.82% vs. 77.63%). Meanwhile, the mean mineralization rate under the nitrate treatment was higher in P. megaterium (77.63%) than in B. pumilus (52.81%), while B. pumilus outperformed P. megaterium in mineralization rate under urea addition over the 0 – 72 h period (51.37% – 70.15% vs. 28.97% – 43.75%); ③ nitrogen input accelerated the transformation of metastable vaterite to calcite in the B. pumilus system, while the P. megaterium system maintained calcite as the dominant phase with relatively consistent crystal polymorph composition. This study elucidates the physiological and mineralogical mechanisms by which nitrogen pollution disrupts microbial carbonate mineralization, providing a theoretical basis for ecological risk assessment under nitrogen deposition scenarios and for the bioremediation of nitrogen-polluted water bodies.