Abstract: Nitrogen (N) is one of the most important nutrients for plants. Its behavior in -soil-plantatmosphere continuum (SPAC) has become a hotspot in recent years. The atmospheric N can enter into plant and soil via biofixation and deposition, and the plant- and soil N can return to atmosphere via ammonia volatili
zation and nitrogenous gaseous emission. After entered into plant via bio-fixation and plant uptake, part of the N abscises from plant organs, and part of it loses via rainwater leaching and plant secretion. The N accumulation and allocation in plant  differ with plant growth stage and plant organ, and the N absorption by plant is limited by the atmospheric and soil status. Through mineralization, nitrification and denitrification, part of soil nitrogen is transformed into the forms that plant can directly use, and part of it loses from soil. Litter decomposition and N deposition can supplement soil N, whereas plant absorption, microbial immobilization, hydrological loss, and nitrogenous secretion can induce the N loss from soil. Litter decomposition, rhizosphere soil, CO₂ concentration, and ozone play important roles in nitrogen cycle. In future research, more attentions should be paid on N pollution, N deposition, and the coupling effec
ts of C and N.

Key words: Forest catchment, Ecological and hydrological process, Dynamic mechanism