Abstract: A pot experiment was conducted to study the effects of applying 0, 240, and 480 kg N·hm^-2 on the cotton leaf antioxidant enzyme activities and endogenous hormone contents under eight days waterlogging at flowering and boll-forming stage. Under this short-term waterlogging, the leaf soluble protein content and SOD and CAT activities decreased while the MDA content and POD activity increased, and in the meantime, the leaf ABA content increased while the ZR, GA, and IAA contents as well as the ZR/ABA, IAA/ABA, and GA/ABA ratios decreased, compared with those under normal watering. Treatment 240 kg N·hm^-2 had the lowest contents of leaf MDA and ABA, but the highest contents of leaf ZR, GA, and IAA, highest ratios of ZR/ABA, GA/ABA, and IAA/ABA, and highest net photosynthetic rate. At the 15th day after terminating waterlogging, no significant differences in the leaf antioxidant enzyme activities, MDA content, and endogenous hormone contents were observed between the short-term waterlogged and well-watered cotton. N application promoted the cotton leaf antioxidant enzyme activities, decreased the MDA and ABA contents, and increased the ZR, GA, and IAA contents as well as the ZR/ABA, IAA/ABA, and GA/ABA ratios, with the highest cotton biomass and yield in treatment 240 kg N·hm^-2.

Key words: cotton, short-term waterlogging, nitrogen application rate, antioxidant enzyme activity, endogenous hormone content, apple, fertilization depth, ¹⁵Nurea, absorption, distribution, utilization, loss.