Combined Effects Of Lanthanum Ion And Acid Rain On Photosynthesis In Rice At Different Growth Stages

Rare earth elements (REEs) pollution and acid rain are important environmental andecological issues, and they attract worldwide attention. These two issues simultaneously existin many regions, especially in some farming areas, causing deleterious effects on plants. Inthis study, the combined effects of lanthanum ion [La(III)] and acid rain on photosyntheticparameters [the net photosynthetic rate (Pn), stomatic conductance (Gs), intercellular CO2concentration (Ci), Hill reaction activity, apparent quantum yield (AQY) carboxylationefficiency (CE)], chlorophyll fluorescence parameters [initial fluorescence (F0), maximalchlorophyll fluorescence (Fv/Fm), electron transport rate of PSII (ETR), effective quantumyield of photochemical energy conversion of PSII (ΦPSII), photochemical quenchingcoefficient (qP), non-photochemical quenching coefficient (qN)] and photosynthetic pigments(the content of chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, and the ratio ofchlorophyll a/b) of rice (Oryza sativa) at different growth stages were investigated by usingPP Systems (International Ltd, UK), PAM-210(Heinz Walz GmbH, Germany) andbiochemical analysis methods. The experimental results were as follows:(1) Compared with the control, the Pn, Gs, Ci, Hill reaction activity, AQY, CE, Fv/Fm,ΦPSII, ETR, qP, qN, the content of chlorophyll a, chlorophyll b, total chlorophyll, carotenoids,and the ratio of chlorophyll a/b in rice at different growth stages were promoted under thesingle treatment of20mg·L-1La(III); and these indices (except the Ci) mentioned above werereduced under the single treatment of300mg·L-1(600mg·L-1) La(III) or pH3.5(pH2.5) acidrain.(2) Compared with the control, the indices mentioned above in rice at different growthstages were improved under the combined treatment of20mg·L-1La(III) and pH4.5acid rain,and were reduced, except the Ci, under the other combined treatments.(3) The effects of La(III) and acid rain on these indices mentioned above in rice atdifferent growth stages were similar. But the change degrees of these test indices showeddifference at different growth stages under the same treatment. The order of changes wasdescribed as follows: for the single treatment of20mg·L-1La(III), as well as the combinedtreatment of20mg·L-1La(III) and acid rain at pH4.5, filling stage> booting stage> tilleringstage> seedling stage; for the treatment of600mg·L-1La(III), as well as the combinedtreatment of300mg·L-1La(III) and acid rain at pH2.5, booting stage>filling stage> seedlingstage> tillering stage; other treatments except the single treatment of acid rain at pH4.5,booting stage> seedling stage> tillering stage>filling stage.In conclusion, the combined treatment of20mg·L-1La(III) and acid rain at pH4.5improved, whereas the other combined treatments (from the combined treatment of20mg·L-1La(III) and acid rain at pH3.5) inhibited the photosynthesis in rice at different growth stages.Moreover, the booting stage among different growth stages was the most sensitive stage to thecombined treatment of La(III) and acid rain, which was an important observation in this study.Furthermore, the continuous treatment of La(III) or acid rain caused more serious effects onthe photosynthesis in rice. These factors should be considered in the assessment for the potential ecological risk of La(III) and acid rain.