Abstract: Inorganic nitrogen is one of the major nutrients in plant growth,especially in artificial revegetation. Robinia pseudoacacia plantation were considered one of the primary and promising trees of artificial revegetation in the Loess Plateau due to its fast growth and ability of fixing atmospheric nitrogen.However,the main form,net transformation rates and dynamics of inorganic nitrogen of Robinia pseudoacacia in the Loess Plateau were still unknown.In this study,we aimed to expose the capability of offering nitrogen through inorganic nitrogen.A chronosequence from 10~40 year-old plantations and adjacent contrasting grasslands in natural control with similar age were selected.The result showed as follows:(1) the average content of NO₃^--N was the 4.57 times in Robinia pseudoacacia plantation than that in the contrasting grasslands,but no influence on NH₄⁺-N. (2) compared with lands and abandoned years,the soil moisture and temperature were the major effects on net transformation rates,showing nitrification was the prominent nitrogen transformation processes on July-August,while ammonization was the key nitrogen transformation processes on April-May and August-September,and Robinia pseudoacacia plantations had faster net nitrogen transformation rates than the contrasting grasslands. (3) Robinia pseudoacacia plantations can accelerate the accumulation of NO₃^--N compared with the grasslands,but a consumption was occurred exceeding 30 year-old.Overall,Robinia pseudoacacia plantation can reduce NO₃^--N leaching,but no influence on NH₄⁺-N,and Robinia pseudoacacia plantation had a consumption trend of NO₃^--N after 30 years.So,some management,such as thinning,should be taken to accelerate the healthy development of Robinia pseudoacacia plantation in the Loess Plateau.

Key words: vegetation restoration, Robinia pseudoacacia, inorganic nitrogen, net transformation rate