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植物光合系统是UV-B辐射最初和最重要的作用靶标。本文在大田条件下进行紫外灯照射处理,研究全生育期UV-B辐射增强(高于环境20%和40%)对棉花形态、干物质积累、光合色素和产量的影响,并通过分析棉花主茎功能叶片的气体交换参数和叶绿素荧光参数,探讨UV-B辐射增强影响棉花光合作用的机制。结果表明,UV-B辐射增强抑制了棉花生长和干物质积累,籽棉产量显著降低,且UV-B辐射越强,抑制作用越明显。随UV-B辐射的增强,棉花主茎功能叶的净光合速率(P_n)在各生育期均显著降低,叶绿素含量呈先升高后降低趋势,气孔导度(Gs)和蒸腾速率(Tr)未发生变化,胞间CO_2浓度(Ci)反而升高,说明P_n下降主要由非气孔限制因素造成。对叶绿素荧光参数的分析表明,PSⅡ的最大光化学量子产率(F_v/F_m)、实际光化学量子效率(ΦPSII)、线性电子传递速率(ETR)和光化学淬灭系数(qP)随着UV-B辐射的增强而降低,非光化学猝灭系数(NPQ)则显著升高,且各叶绿素荧光参数与Pn变化均显著相关;慢速弛豫NPQ(NPQS)及其在NPQ中的比例均随UV-B辐射的增强而显著提高,表明PSⅡ反应中心受损,光化学效率降低。以上结果证明,全生育期UV-B辐射增强降低了棉花的光合叶面积、叶绿素含量和净光合速率,引起棉花生长与物质积累受抑,产量降低。UV-B辐射增强引起的光合速率下降与PSⅡ反应中心遭到破坏密切相关。
Plant photosynthetic systems are the first and most important targets of UV-B radiation. The effects of UV-B radiation during the whole growth period (higher than 20% and 40% of the environment) on the morphology, dry matter accumulation, photosynthetic pigment and yield of cotton were studied in this paper. Gas exchange parameters and chlorophyll fluorescence parameters of stem functional leaves, and to explore the mechanism of enhanced UV-B radiation affecting photosynthesis of cotton. The results showed that enhanced UV-B radiation inhibited cotton growth and dry matter accumulation, the seed cotton yield was significantly reduced, and the stronger the UV-B radiation, the more obvious the inhibition. With the increase of UV-B radiation, net photosynthetic rate (P_n) of functional leaves of cotton main stem decreased significantly at all growth stages, chlorophyll content increased first and then decreased, stomatal conductance (Gs) and transpiration rate (Tr) No change, the intercellular CO 2 concentration (Ci) but increased, indicating P_n decline mainly caused by non-stomatal limitations. The analysis of chlorophyll fluorescence parameters showed that the maximum photochemical quantum yield (F_v / F_m), actual photochemical quantum efficiency (ΦPSII), linear electron transfer rate (ETR) and photochemical quenching coefficient (qP) (NPQ) increased significantly, and each chlorophyll fluorescence parameter and Pn changes were significantly correlated; slow relaxation NPQ (NPQS) and its proportion in NPQ with UV-B Increased radiation and significantly increased, indicating PS Ⅱ reaction center damage, photochemical efficiency decreased. The above results show that enhanced UV-B radiation during the whole growth period reduces the photosynthetic leaf area, chlorophyll content and net photosynthetic rate of cotton, causing the cotton growth and material accumulation to be inhibited and the yield reduced. The decrease of photosynthetic rate caused by enhanced UV-B radiation is closely related to the destruction of PSⅡ reaction center.