Abstract: Migration of nitrogen through runoff from cropland to river results in low utilization of fertilizer as well as water pollution and eutrophication. Proper riparian vegetation buffering between riverbank and cropland could protect the aquatic ecosystems. Four types of vegetation buffer strips (Artemisia strip, Lolium perenne strip, Salix integra +L. prenne strip, and Amorpha fruticosa +L. perenne strip) were constructed in Liaohe River protected area close to cropland. We measured the removal efficiency of runoff volume, suspended solids (SS), NO₃^--N, NH₄⁺-N and TN in runoff and ground water. The results showed that, with increasing riparian vegetation strip width, the removal rate of runoff volume, SS, and nitrogen increased. A 5mwidth L. perenne strip reduced SS by 69.1%, while a 5mwidth A. fruticosa+L. perenne strip removed 57.6% of NO₃^--N in runoff. Vegetation strips with 13mwidth averagely reduced SS, NH₄⁺-N, NO₃^--N and TN by 95.6%, 91.3%, 75.9%, and 82.9%, respectively. The removal rate of N in runoff was significantly lower than that in ground water. The removal rate of NO₃^--N and TN in ground water within 5mwidth vegetation strip recorded negative value, indicating that vegetation buffer strengthens infiltration of nonpoint source N and thus increases the risk of NO₃^--N loss in subsurface flow. Among the four types of vegetation buffers, A. fruticosa+L. perenne strip had the highest removal efficiency of N in runoff and ground water.

Key words: sodium nitroprusside, iron deficiency, tomato seedlings, antioxidant enzyme., NO₃^- stress, nutrients uptake