光强对三七光合能力及能量分配的影响

Effects of light intensity on photosynthetic capacity and light energy allocation in Panax notoginseng

通过研究生长于不同环境光强(29.8%、9.6%、5.0%、1.4%和0.2%全日照)下的2年生三七光合作用对光照强度、CO_2浓度、模拟光斑的响应及叶绿素荧光和能量分配特征,研究光照强度对阴生植物三七光合特征及光适应的影响.结果表明:29.8%全日照(FL)下三七表观量子效率(AQY)、光系统Ⅱ(PSⅡ)潜在的量子效率(F_v/F_m)、PSⅡ潜在活性(F_v/F_o)较低,最大净光合速率(P_(n max))、最大电子传递速率(J_(max))、实际光化学量子效率(F/F_m')、电子传递速率(ETR)、光化学淬灭系数(q_P)和光能分配到光化学途径的比例(Φ_(PSⅡ))较高,但非光化学淬灭系数(NPQ)并不是最高.9.6%FL和5.0%FL处理P_(n max)、光补偿点(LCP)、光饱和点(LSP)、暗呼吸速率(Rd)无显著差异,但它们的AQY、羧化效率(CE)、最大羧化速率(V_(c max))、F_v/F_m、F_v/F_o较高,NPQ也相对较高.生长环境光强低于5.0%FL时,P_(n max)、CE、V_(c max)、J_(max)、ETR、F/F)m'、q_P、NPQ和Φ_(PSⅡ)均随生长环境光强的降低呈下降趋势,而捕获的光能分配到荧光耗散的比例(Φ_(f,D))逐渐增加.在500μmol·m^(-2)·s^(-1)光斑诱导下,生长环境光强大于5.0%FL下的三七Φ_(PSⅡ)随诱导时间的延长缓慢增加,1.4%FL和0.2%FL下Φ_(PSⅡ)迅速达到饱和,且Φ_(f,D)迅速增加.三七在受到长期高光胁迫的环境下,通过适度的PSⅡ光抑制和保持较高光合电子传递速率,从而提高光能的利用来保护光合机构遭受不可修复的氧化伤害;适度的遮荫能够有效保持较高的非光化学热耗散能力;但过度遮荫会使其光合能力明显降低,捕获的光能更多地通过非光化学的途径耗散,且在接受到高光照射时较容易引发光氧化伤害.

To explore the effects of light intensity on photosynthetic characteristics and light adaptation of the shade-demanding species Panax notoginseng, the responses of photosynthesis to photosynthetic photon flux density, CO2 and sunflecks in the two-year-old Panax notoginseng were investigated under different levels of light intensity （29.8%, 9.6%, 5.0%, 1.4% and 0.2% of full sunlight）. Meanwhile, chlorophyll a fluorescence parameter and light energy partitioning were also recorded and calculated in the responsive process. P. notoginseng grown under 29.8% full sunlight （FL） had a lower apparent quantum yield （AQY）, potential photochemical quantum yield （Fv/Fm） and potential photochemical activity （Fv/Fo）, however, it had a higher maximum net photosynthetic rate （Pn max）, maximum electron transport rate （Jmax）, F/Fm′, electron transport rate （ETR）, photochemical quenching （qP） and the proportion of light energy allocated to photochemistry dissipation （ΦPSⅡ）, but the non-photochemical quenching （NPQ） was not the highest. There were no significant differences in Pn max, light compensation point （LCP）, light saturation point （LSP）, dark respiration rate （Rd） among 9.6%FL and 5.0% FL treatments, but these treatments had relatively higher values of NPQ, AQY, carboxylation efficiency （CE）, maximum carboxylation rate （Vc max）, Fv/Fm and Fv/Fo. In addition, the Pn max, CE, Vc max, Jmax, ETR,F/Fm′, qP, NPQ and ΦPSII decreased with the decrease in light intensity from 5.0%FL to 0.2%FL, and the proportion of light energy allocated to fluorescent dissipation （Φf,d） were increased. Under 500 μmol·m-2·s-1 light-flecks inducting, the ΦPSⅡ of P. notoginseng increased slowly with the extension of time except for the treatment of less than 5.0%FL, and under the circumstance of 1.4%FL and 0.2%FL, ΦPSⅡ reached significantly a perfect result, moreover, Φf,d increased rapidly. These results suggested that the enhancement in photosynthetic electron transport to use the light energy and the moderate photoinhibition of PSⅡ might avoid the irreversible oxidative damage of photosynthetic organization in P. notoginseng under high levels of light intensity. Moderate shading was beneficial to maintain its higher non-photochemical quenching ability. However, its photosynthetic capacity depressed and the proportion of light energy allocated to non-photochemical pathway increased obviously in excessive shading, and it easily caused a light oxidative damage.