The maximum chlorophyll fluorescence yield under illumination (Fm') is one of the most important parameters in plant eco-physiological research, and usually was estimated with rectangular flush scheme (RF). However, the estimation accuracy of RF for Fm' was affected by the rapid turnover of photosystem 2 (PS2). In order to eliminate the effect of the rapid turnover of photosystem 2 (PS2), the multiphase flush scheme (MPF) based on the linear relationship between the flush (Q') and chlorophyll fluorescence (F') is proposed to estimate Fm' at infinite irradiance. Leaf gas exchange and chlorophyll fluorescence of three woody species (Castanopsis sclerophylla, Cyclobalanopsis glauca, and Sapium sebiferum) were respectively measured with RF and MPF, Fm' and the derived parameters [the quantum efficiency of PS2 (ΦPSII), the electron flux through PS2 (J), the maximum electron transfer rate (Jmax), mesophyll conductance (gm) and chloroplast CO2 concentration (Cc)] were compared between the two different schemes, and the effects of RF and MPF on these parameters were analyzed. The results showed that no significant difference was found in the parameters for the three species between RF and MPF at the light intensity lower than 200 μmol·m-2·s-1. Fm' estimated with MPF for the three species were 3.5%-5.2%, 11.7%-18.0%, and 3.2%-7.1% higher than those with RF, respectively, at the light intensity higher than 200 μmol·m-2·s-1. The derived parameters (ΦPSII, J and Jmax) estimated with MPF for the three species were higher than those with RF, while the derived parameters(gm and Cc) estimated with MPF were lower at the light intensity higher than 200 μmol·m-2·s-1. In conclusion, estimates of parameters (Fm', ΦPSII, and J) were not significantly affected by the two different schemes at the light intensity lower than 200 μmol·m-2·s-1. The estimates of parameters (Fm', ΦPSII, J, Jmax, gm, and Cc) were significantly affected by the two different schemes at the light intensity higher than 200 μmol·m-2·s-1. Compared with MPF, parameters of Fm', ΦPSII, J and Jmax estimated with RF were underestimated, while parameters of gm and Cc were overestimated.
光下最大荧光(Fm′)是植物生理生态研究中的重要参数,一般采用饱和脉冲(RF)方案来估计.然而,光系统Ⅱ(PSⅡ)受体库的反馈调节会影响RF方案对Fm′估计的准确性.为消除PSⅡ受体库反馈调节的影响,根据光脉冲强度(Q′)与叶绿素荧光(F′)的线性关系提出多相脉冲(MPF)方案,估算Q′无穷大时的F′(即Fm′).本研究采用MPF和RF方案分别对苦槠、青冈和乌桕3个树种叶片的叶绿素荧光和气体交换数据进行同步测量,并对两种方案估计的Fm′及其计算参数PSⅡ光化学效率(ΦPSII)、PSⅡ的电子传递速率(J)、最大电子传递速率(Jmax)、叶肉导度(gm)和叶绿体内CO2浓度(Cc)等光合参数进行比较,分析两种方案对3个树种叶片6个光合参数的影响.结果表明: 当光合有效辐射(PAR)＜200 μmol·m-2·s-1时,两种方案对苦槠、青冈和乌桕叶片Fm′、ΦPSII和J的估计无显著影响;当PAR>200 μmol·m-2·s-1时,采用MPF方案获得的苦槠、青冈和乌桕的Fm′分别比RF方案获得的Fm′高3.5%～5.2%、11.7%～18.0%和3.2%～7.1%;当PAR>200 μmol·m-2·s-1时,采用MPF方案获得的ΦPSII、J和Jmax分别不同程度地大于RF方案获得的参数,gm和Cc分别不同程度地小于RF方案获得的参数.说明当PAR较低(＜200μmol·m-2·s-1)时,MPF与RF方案对植物叶片Fm′、ΦPSII、J的估计没有显著影响;当PAR较高(≥200μmol·m-2·s-1)时,MPF与RF方案对植物叶片Fm′、ΦPSII、J、Jmax、gm和Cc的估计有显著影响,且RF方案对植物叶片的Fm′、ΦPSII、J和Jmax比MPF方案分别有不同程度的低估,对gm和Cc则有不同程度的高估.
Keywords: maximum chlorophyll fluorescence under illumination; multiphase flush; photosynthetic parameters; rectangular flush.