中文摘要：

大田原位种植元阳梯田2个地方水稻品种——白脚老粳和月亮谷,研究2年不同强度（0、2.5、5.0和7.5 k J·m^-2）UV-B辐射对水稻穗下第1至第4节的茎秆性状（节间长、茎秆粗和茎壁厚）和倒伏指数的影响.结果表明：增强UV-B辐射对水稻茎秆的节间长和茎秆粗没有显著影响,但导致茎壁厚度显著减小,其中,7.5 k J·m^-2UV-B辐射对水稻穗下第4节茎秆茎壁厚度的影响较大,降幅为11.6%-19.6%;增强UV-B辐射导致水稻茎秆的倒伏指数增加,增大水稻倒伏的风险,水稻穗下第4节茎秆倒伏指数最大,并大于倒伏临界值（200）;水稻穗下第4节、第3节和第2节茎秆的倒伏指数与茎壁厚度呈显著负相关.表明增强UV-B辐射显著减小元阳梯田水稻茎秆的茎壁厚是增加其倒伏风险的主要原因.

英文摘要：

Two local rice varieties （ Baijiaolaojing and Yuelianggu） were cultivated in situ in Yuan- yang terraces, China, in 2012 and 2013 to investigate the effect of enhanced UV-B radiation condi- tion （0, 2.5, 5.0 and 7.5 kJ·m^-2） on internode characteristics including length, culm diameter, culm wall thickness from the first to the fourth internode, as well as the lodging index. The results showed that UV-B radiation had no significant influence on intemode length and culm, but signifi- cantly reduced the culm wall thickness, with that of the fourth internode region decreased by 11.6% to 19.6% under 7.5 kJ·m^-2 UV-B radiation. The enhanced UV-B radiation increased the lodging index of rice varieties, making them more prone to lodging. The fourth internode had the highest lodging index which was higher than the lodging critical value （200）. The decrease in culm wall thickness due to the enhanced UV-B radiation could be responsible for the increasing lodging risk of rice varieties grown in Yuanyang terraces.