Long-term exzogenous nitrogen (N) input into terrestrial ecosystems causes changes in carbon storage in plant and soil pools. However, little is known how input of N with different chamical forms could influence patterns of photosynthetic carbon (C) allocated into dofferent pools, such as above- and below-ground plant tissues, soil, and soil respiration. In particular, the mechanisms underlying changes in plant and soil carbon storage in responses to N input are not clear. A long-term fertilizaiton experiment of N with different chemical forms was carried out in an alpine meadow on the Tibetan Plateau. We tested the patterns of photosynthetic carbon allocated into plant tissues, soil, and soil respiration using ¹³C tracing experiment in the field. Our results showed that N input with different chemical forms caused changes in the patterns of photosynthetic C allocated into above- and below-ground plant tissues. Moreover, allocation of photosynthetic C into soil differed in response to different chemical forms of N, and the C-CO₂ fluxes were significantly different regarding to the N chemical forms. Specifically, significant differences in patterns of photosynthetic C allocated into different pools were found between ammonium-N and nitrate-N treatments. Comparison with ammonium-N, relatively faster transition of photosynthetic C was found in nitrate-N treatment, and photosynthetic C was fastly respired via soil respiration. The results from ¹³C labeling are corresponding to the significantly high carbon stored in plant root and soil in ammonium-N than in nitrate-N treatments. Our results showed that aboveground biomass in ammonia-N treatment were 49.5% higher than that in the control treatment as N addition treatments have been performed for 10 years. Meanwhile, belowground biomass in ammonia-N treatment were 111.3% higher than that in the control treatment. The ¹³C retained in the soil showed a downward trend during the 30 days, and the soil carbon pool in ammonia-N treatment was significantly higher than that in nitrate-N treatment. The ¹³C efflux from soil respiration with time followed an exponential decay function in each one of the treatments. Among them, decay rate of ¹³C in nitrate-N treatment was the fastest one. On the first day after ¹³C isotope labeling, ¹³C in plant shoots was ammounted to about 80% of the ¹³C in the shoots after the immidiate labeling. There was no significant difference in ¹³C in plant shoots on the first day after labeling between different treatments. On the 30th day, the retention of ¹³C in shoots was reduced to about 30% of the initial amount. The values in nitrate-N treatment were significantly lower than those in the control and ammonia-N treatments from day 21 to 30. The results showed that the photosynthetic C fixed by plants was rapidly transported into underground tissues and soil in a short period of time in the treatment of nitrate-N addition. Our results illustrate the responses of allocation in photosynthetic C to N input with different chemical forms. We also quantified the rate of C-CO₂ efflux via soil respiration, which is critical to understand clearly about the contribution of photosynthetic C to soil carbon stroage. The results can be used to develop more resonable policy in grassland management, which are benefial for sustable development of the alpine grasslands.