【摘要】 以西瓜品种早佳8424为试材,分别在中度低温(15℃/10℃)和重度低温(10℃/5℃)下进行处理,研究不同程度低温胁迫对西瓜幼苗光合作用和叶绿素荧光特性的影响。结果表明:(1)低温胁迫下,叶绿素(a+b)含量、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)均逐步下降,低温胁迫越重,光合参数下降幅度越大。在重度低温胁迫6 d后其Pn降至1.56,相比处理前下降85.9%,表明重度低温已严重损害叶片光合机构,极大抑制了光合作用。(2)中度低温下胞间CO2浓度(Ci)降低,与Pn、Gs变化趋势一致,故气孔限制是导致其光合速率降低的主要因素;而重度低温胁迫下Ci呈现相反上升趋势,表明其光合速率降低是由非气孔限制因素导致。低温处理均增加了叶绿素a/b,可能是西瓜幼苗对光照下低温胁迫的一种自我保护机制,因为相对少量叶绿素b能避免过多吸收光能而导致光抑制。(3)低温胁迫降低了叶片PSⅡ最大光化学效率(Fv/Fm)和光化学淬灭系数(qP),重度低温下非光化学淬灭系数(qN)随之下降,而中度低温下qN则表现为升高,表明中度低温胁迫下西瓜幼苗能通过叶黄素循环的热耗散途径来消除天线色素捕获的过多光能以减轻对PSⅡ的伤害,而重度低温胁迫下幼苗的这种光保护机制已丧失,其对叶片的光合机构将造成不可逆的伤害。更多还原

【Abstract】 The effects of moderate low temperature(15℃/10℃, day/night) and severe low temperature(10℃/5℃, day/night)on photosynthesis and chlorophyll fluorescence characteristics were studied in watermelon cultivar ‘Zaojia8424’. The results showed that:(1) The chlorophyll(a+b) content, net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs) were gradually decreased under low temperature stress, and the lower the temperature was, the greater the photosynthetic parameters decreased. Severe low temperature stress reduced Pnto 1.56 and decreased by 85.9% compared to non-stress after 6 d of treatment, indicating that severe low temperature caused serious damage to photosynthetic apparatus of watermelon seedlings and greatly inhibited the photosynthesis.(2) Intercellular CO2concentration(Ci) shown to decrease under moderate low temperature stress, consistent with the change trend of Pnand Gs, indicating that stomatal restriction was the main factor leading to reduction of photosynthetic rate. However, severe low temperature stress increased Ci, demonstrating a fact that non-stomatal restriction was the main factor for the decrease of Pn. The chlorophyll a/b increased under low temperature stress, which may be a self-protective mechanism of watermelon seedlings to low temperature with light stress, because the relatively small amount of chlorophyll b could avoid photoinhibition caused by excessive light absorbed by chlorophyll.(3) Low temperature stress led a significant decline in the maximum photochemical efficiency of photosystem Ⅱ(Fv/Fm) and photochemical quenching coefficient(qP), severe low temperature stress also caused a decrease in the non-photochemical quenching coefficient(qN), whereas qN showed a increase under moderate low temperature stress. This suggested that watermelon seedlings grown under moderate low temperature could consume excessive light energy absorbed by antenna pigment through thermal dissipation in xanthophylls cycle to alleviate the damage of PS Ⅱ, whereas under severe low temperature stress, the photo-protective mechanisms of watermelon seedlings destroyed and it also caused a irreversible damage to photosynthetic apparatus.更多还原