采用水培方式研究了LaCl3对140 mmol·L-1 NO3-硝酸盐胁迫下黄瓜幼苗光合特性的影响.结果表明: 硝酸盐胁迫显著降低了黄瓜幼苗叶绿素及类胡萝卜素含量，叶片Mg2+ ATPase、Ca2+ATPase活性也随之降低；硝酸盐胁迫7 d，黄瓜幼苗叶片光合速率的降低以气孔限制为主，叶片AQY与CE下降，胁迫12 d则以非气孔限制为主.硝酸盐胁迫下，外加LaCl3可以使黄瓜叶片保持较高的Mg2+ATPase、Ca2+ATPase活性及叶绿素和类胡萝卜素含量，尤其是外加低浓度（20 μmol·L-1）LaCl3显著增加了叶片类胡萝卜素含量；LaCl3还具有降低气孔关闭、改善叶片气体交换功能，减缓叶片Fv/Fm、ФPSII、AQY、CE及qP的降低幅度等作用，使叶片在盐胁迫下保持较高的光能利用率及CO2同化能力.20 μmol·L-1 LaCl3可以有效缓解硝酸盐对黄瓜幼苗光合作用的影响，而200 μmol·L-1LaCl3在胁迫初期对黄瓜幼苗有缓解效果，后期则效果不明显.该结果可为设施土壤的改良提供新的途径.
By the method of hydroponic culture, this paper studied the alleviation effects of LaCl3 on the photosynthetic characteristics of cucumber seedlings
under nitrate (140 mmol NO3-·L-1) stress, with the related mechanisms discussed. Under nitrate stress, the seedlings leaf chlorophyll and carotenoids contents decreased significantly, and the leaf Mg2+ATPase, Ca2+ATPase activities also decreased. On the 7th day of nitrate stress, the decrease of seedlings photosynthetic rate was mainly due to stomatal limitation; but on the 12th day of nitrate stress, the decrease was mainly due to no-stomatal limitation. Supplement with LaCl3 could make the cucumber seedlings keep relatively higher leaf Mg2+-ATPase and Ca2+-ATPase activities and chlorophyll and carotenoids contents, and applying 20 μmol·L-1 of LaCl3 could increase the carotenoids content significantly. LaCl3 could also improve the leaf gas exchange, and alleviate the decrease of leaf Fv/Fm, ФPSII, AQY, CE, and qp under nitrate stress, which helped the lea
ves making good use of light energy and maintaining higher CO2 assimilation capacity. An additional 20 μmol·L-1 of LaCl3 could alleviate the nitrate
stress on the photosynthesis of cucumber seedlings efficiently, but an additional 200 μmol·L-1 of LaCl3 only had the alleviation effect at the initia
l period of nitrate stress. Our results could benefit to the improvement of greenhouse soil.