Abstract: With the target CO₂ concentration of FACE plots being 200 μmol·mol^-1 above that in ambient air, this paper studied the effect of free-air CO₂ enrichment (FACE) on leaf nitrate reductase activity (NRA) of Oryza sativa L. cultivar Wuxianjing 14. The results showed that FACE obviously increased the NRA of functional leaves at all growth stages, with an average increment of 50%, 20%, 60%, 80% and 30% at the stages of jointing, booting, heading, 10 after heading, and 20 days after heading, respectively, showing a pronounced effect at jointing,heading and 10 days after heading. Nitrogen application rate also had an obvious effect on the absolute value of NRA in functional leaves under FACE condition. The magnitude of NRA in three nitrogen treatments was in the order of normal nitrogen (NN)＞low nitrogen (LN)＞high nitrogen (HN) at jointing stage, HN＞NN＞LN at both booting and heading stages, and NN＞HN＞LN at both 10 days and 20 days after heading, respectively. The interactive effect of FACE and N supply on NAR varied with the growth stage of Wuxianjing 14, being very significant or significant at the stages of jointing and 20 and 10 days after heading, but not significant at booting and heading stages.

Key words: Chlorine dioxide, Algaecide, Phaeocystis globosa, Red tide