A review on nitrogen transmission processes in natural wetlands
湿地氮素传输过程研究进展

Wetlands are the most active interface for energy exchange and material movement on the earth, since they are the ecotones between waters and inlands. Nitrogen, one of the important components of wetland soils, is an ecological factor of wetland ecosystems that greatly influence the productivities of wetland ecosystems. The present paper aims to provide a critical review on nitrogen movement and transformation in wetland ecosystems. Nitrogen transmission includes physical, chemical and biological processes, which are closely linked to soil formation and plant growth and consists of a complex network with substance cycles and energy flow in these air- water-soil-life systems. It is a considerable threaten for nitrogen leaching to water quality safety of ground water in wetlands. Wetlands act as sink or source of nitrogen, which is controlled by such environmental factors as soil characteristics or water properties. Ammonia volatilization is one path of nitrogen loss and is greatly related to pH values of waters. Nitrogen mineralization, nitrification and denitrification are main chemical transformation processes and related to each other. They are the main mechanisms of mineral nutrients supply and N_2O emissions, which are greatly influenced by the environmental factors and human activities and can be described by kinetics models. Wetland vegetation's uptake and accumulation and microbial decomposition play the important roles in nitrogen cycles of wetlands. Some nitrogen processes in wetlands have been greatly considered in the past studies, but it is necessary to study comprehensively and continuously nitrogen biogeochemical processes in the future. The key research fields are as follows: (1) nitrogen movement and transformation processes in wetlands with different vegetation types; (2) relationships between nitrogen transmission processes and global changes; (3) effects of LUCC on nitrogen biogeochemical processes; (4) processes and mechanisms of wetland hydrology patterns influencing on nitrogen transmission processes; (5) nitrogen retaining and purification mechanisms of wetland soils; (6) biogeochemical processes and ecological effects of nitrogen cycling in plateau wetlands.