大葉石龍尾(Limnophila rugosa (Roth) Merr.)又稱大葉田香草，在台灣為零星分佈，主要在低海拔山帶的池塘、稻田、湖沼、溼地、水邊等潮濕環境。大葉石龍尾為傳統中草藥植物，並為深具發展潛力的原生香草。本研究以大葉石龍尾為研究材料，探討不同濃度的氮肥處理對大葉石龍尾葉片抗氧化能力及黃嘌呤氧化酶抑制活性之影響。試驗結果顯示大葉石龍尾之光合色素包括葉綠素 a、葉綠素 b及類胡蘿蔔素含量皆隨著氮肥用量增加而顯著增多，同時總葉綠素指數亦增加。抗氧化能力包括α,α-diphenyl-β-picrylhydrazyl (DPPH)自由基清除能力、亞鐵離子螯合能力及還原力等隨著氮肥用量增加而顯著升高。增施氮肥可以促進大葉石龍尾抑制黃嘌呤氧化酶的活性，氮肥等級0.1X、0.5X、1X 處理下大葉石龍尾抑制黃嘌呤氧化酶分別為28.1%、46.4%及72.3%。大葉石龍尾萃取物亦隨著濃度增加而增強對黃嘌呤氧化酶的抑制能力，大葉石龍尾於0.5X 氮肥等級處理下，其萃取物隨濃度增加，對黃嘌呤氧化酶的抑制率有上升的趨勢，於8.38 mg ml-1 時對黃嘌呤氧化酶的抑制率達86%，其IC50 約為5.87 mg ml-1，而常用降尿酸藥物安樂普利諾IC50為3.80 μg ml-1。本研究首次分析大葉石龍尾葉片萃取物抑制黃嘌呤氧化酶之效果，研究結果可提供未來醫學保健以及農業方面研究之參考。

Limnophila rugosa (Roth) Merr. is scattered mainly in the lower altitude mountain of Taiwan near ponds, paddy fields, lakes, wetlands, and humid environment. As a native herb with many potential developments, L. rugosa is traditionally used as a medicinal plant. This study focused the effects of various nitrogen application rates (0.1X, 0.5X and 1X N of Kimura solution) on antioxidative activities of L. rugosa. and its inhibitory activity on xanthine oxidase (XO). The increase of chlorophyll index caused by raising chlorophyll a and b and carotenoid contents with increasing nitrogen rate was found. The antioxidative activities including α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging activity, Fe2+ ion chelating activity and reducing power were significantly increased by increasing nitrogen rate. An improvement of XO activity inhibition was found with increasing nitrogen rate. The ethanol extracts of L. rugosa treated with 0.1X, 0.5X and 1X nitrogen rate inhibited XO by 28.1%, 46.4% and 72.3%, respectively. The inhibition effect of these extracts increased with the increase of extract concentration. The 8.38 mg ml-1 extract of L. rugosa from 0.5X nitrogen treatment inhibited xanthine oxidase by 86% with an IC50 of 5.87 mg ml-1 compared with an IC50 of 3.80 μg ml-1 for allopurinol. This is also the first report to demonstrate that L. rugosa has an ability to inhibit XO activity. The results of this study will provide useful information for medical care and agriculture technology.