Research Progress on Soluble Organic Nitrogen Pool in Soil and Its Functions in Forestry Ecosystem

This paper reviews the recent research progress in China and abroad on the pool size, composition and eco-functions of the soluble organic nitrogen (SON) in soil in the forestry ecosystem.The SON content in forest soil varied with soils, forest types, climate conditions and analytical methods.The soil SON content in the mineral layer is generally between 1 mgkg-1 and 87 mgkg-1.It ranges from 23 mgkg-1 to 448 mgkg-1 in the organic layer.They account for 16%-96% of the total soluble nitrogen in the soil.Soil SON includes a mixture of nitrogenous compounds of different structure, including ammonia nitrogen, amino acids and ammonia sugar.Forest plants can utilize low molecular weight SON(such as artificial fertilization of amino acids).However, no evidence has been shown that the plants could directly absorb the natural SON in soil.Forest soil SON is a very important nitrogen source.It plays a significant role in the nitrogen cycle in the forestry ecosystem.Future research on forest soil SON should focus on chemical and biological properties of SON, dynamic characteristics of soil natural SON, nutritional functions of the natural SON in N-limited forestry ecosystem, eco-function evaluation of SON, impact of microorganisms on SON kinetics in the forest ecosystem and direct uptake of SON by forest plants.