遮阴和盐分对银叶树幼苗光合特性与叶绿素荧光参数的影响

通过比较不同光和盐水平下银叶树(Heritiera littoralis)幼苗的叶绿素含量、光合光响应参数及叶绿素荧光参数的差异,探讨了遮阴和施盐处理下银叶树幼苗的光合生理及适应能力。以银叶树盆栽幼苗为研究对象,以全光无盐为对照,设置遮阴(遮光率为80%)与2.5%盐水处理,经60 d的处理,测定其光合光响应参数、叶绿素荧光参数及叶绿素含量。结果表明,在正常环境下,银叶树光饱和点(LSP)、光补偿点(LCP)及Chla/b分别为1023、28.8μmol·m^?2·s^?1及3.65,属阳性树种。在无盐条件下,遮阴处理导致了叶片叶绿素含量、表观量子效率(AQY)、PSⅡ潜在活性(Fv/Fo)、PSII最大光化学效率(Fv/Fm)及PSⅡ有效光化学量子产量(Fv'/Fm')的升高,却降低了Chl a/b、最大净光合速率(P′max)、LSP、LCP、暗呼吸速率(Rd)、初始荧光(Fo)、PSⅡ实际光合效率(ΦPSⅡ)、表观光合量子传递效率(ETR)、光化学猝灭系数(qP)及非光化学淬灭系数(NPQ)。在全光照或80%的遮阴环境下,盐胁迫均使得叶片叶绿素含量、光合光响应参数(AQY、P′max、LSP)及叶绿素荧光参数(Fm、Fv/Fo)显著下降(P<0.05);而在全光环境下,盐胁迫同样显著降低了Fv/Fm、ΦPSⅡ、ETR(P<0.05),但在遮阴环境下,盐胁迫并没有显著降低叶片Fv/Fm、Fv′/Fm′、ΦPSⅡ及ETR(P>0.05)。盐分对叶片叶绿素含量、光合光响应参数(AQY、P′max及LSP)及叶绿素荧光参数(Fo、Fm、Fv、Fv/Fo、ΦPSⅡ、ETR及NPQ)的影响高于光照,光和盐对叶绿素含量、光合光响应参数(AQY、P′max及LSP)及叶绿素荧光参数的影响没有交互作用。研究表明,银叶树幼苗表现出较高的耐阴性及对弱光的利用能力;盐胁迫使银叶树幼苗发生了明显的光抑制,PSII的光化学活性降低,过剩光能对光系统的破坏的风险增加,光能转换效率与电子传递能力下降,光合作用效率大幅降低。

Effects of Shade and Salt on Photosynthesis and Chlorophyll Fluorescence of Heritiera littoralis Seedling

By comparing the impact of shade and salt treatments on photosynthesis and chlorophyll fluorescence parameters of Heritiera littoralis seedlings,this study aims to explore the adaptive capacity of H.littoralis seedlings to shade and salinity stress.We manipulated light penetration(full light and 80%shade)and salt(no salt addition and 2.5% salt water addition)in a 60-day greenhouse experiment,and measured light response curve,chlorophyll content and chlorophyll fluorescence for each seedling.The results showed that under control treatment with full light and no salt addition,the light saturation point,light compensation point and Chla/b were 1023μmol·m^?2·s^?1,28.8μmol·m^?2·s^?1 and 3.65,respectively,indicating that H.littoralis is heliophyte.Under no salt addition condition,shade treatment increased the content of chlorophyll,apparent quantum yield(AQY),PSⅡpotential activity(Fv/Fo),PSⅡmaximum photochemical efficiency(Fv/Fm)and PSⅡeffective photochemical quantum yield(Fv′/Fm′),but decreased Chla/b,maximum net photosynthetic rate(P′max),light saturation point(LSP),light compensation point(LCP),respiration rate(Rd),initial fluorescence(Fo),PSⅡactual photosynthetic efficiency(ΦPSⅡ),apparent photosynthetic quantum transfer efficiency(ETR),photochemical quenching coefficient(qP)and non-photochemical quenching coefficient(NPQ).Under full light and 80%shade environments,salt treatment significantly decreased the content of chlorophyll,photosynthetic response parameters(AQY,P′max,LSP)and chlorophyll fluorescence parameters(Fm,Fv/Fo)(P<0.05).Under full light environment,salt treatment significantly decreased Fv/Fm,ΦPSⅡand ETR(P<0.05);but under shade environment,salt treatment did not significantly decreased Fv/Fm,Fv′/Fm′,ΦPSⅡand ETR(P>0.05).The influence of salt treatment on the content of chlorophyll,photosynthetic response parameters(AQY,P′max,LSP)and chlorophyll fluorescence parameters(Fo,Fm,Fv,Fv/Fo,ΦPSⅡ,ETR and NPQ)was greater than that of light treatment,and the interaction effect of light and salt treatments on the above parameters was not significant.This study suggests that,H.littoralis is highly shade-tolerant and is able to utilize low level of light.This study also suggests that salinity stress induces significant photoinhibition in H.littoralis seedlings,evidenced by decreases in PSⅡpotential activity,light energy exchanging efficiency,electron transport capacity,and a resulting decrease in photosynthetic efficiency.