| Photosynthesis is the basis for the study of plant growth. The ultimate goal of studyingplant is increasing production. Rational using of plant hormones and growth regulators canaffect plant growth and adaptation to the environment. The research of plant hormones is animportant theoretical idea for crop genetic improvement, that it plays an revolutionary role inplant genetic improvement and breeding. In this study, four northern conventional soybeancultivars were used to cut from the stem base, and then placed them in to nutrient solutioncontaining cytokinin (CTK), abscisic acid (ABA) and auxin(IAA) respectively and cultured atdifferent growth stages, which aim to simulate the influence of root on leaf photosynthesis. Thisstudy was desired to explore the reason for the changes of soybean photosynthesis, and providecertain theoretical basis of soybean high yield cultivation techniques.The results were as follows:1、Effects of different exogenous hormones on net photosynthesis rate (Pn) of soybeanleavesCTK and IAA enhanced Pn, while ABA inhibited Pn. The changes of Pnshowed a singlepeak curve with advancing of growth stages, which was increased first, and then decreased. Itreached maximum at R4growth stage and then gradually declined.2、Effects of different exogenous hormones on intercellular CO2concentration (Ci) ofsoybean leaves.The effects of CTK and IAA on intercellular CO2concentration (Ci) were both not obvious inJilin35and Jilin36at V4stage, but it was obvious in Silihuang and Jilin38. The effects of ABAon intercellular CO2concentration (Ci) were all obvious in four soybean leaves. Effect of CTKand IAA on intercellular CO2concentration (Ci) of leaves was not significant, but it wassignificant under ABA treatment at R2, R4and R6stage.3、Effects of different exogenous hormones on transpiration rate（Tr）of soybean leavesThe transpiration rate（Tr）increased with the treatment of CTK and IAAat different growthstages in different soybean cultivars, while Trdecreased with the treatment of ABA4、Effects of different exogenous hormones on stomatal conductance (Gs) of soybean leavesEffects of different exogenous hormones on stomatal conductance (Gs) of isolated soybeanleaves were significant. CTK and IAA enhanced Gs, but ABA inhibited it. The changes of Gsshowed a single peak curve with advancing of growth stages, which was increased first, and then decreased. It reached maximum at R4growth stage and then gradually declined. Changesof Gsshowed the same tendency with the treatment of different exogenous hormones. Itsuggested that R4is the most active period for soybean growth.5、Effect of different exogenous hormones on water use efficiency (WUE) of isolatedsoybean plant.Different effect was showed in water use efficiency (WUE) of soybean plant leaves atdifferent exogenous hormones. IAA and CTK could promote water use efficiency (WUE), butABA could inhibit water use efficiency (WUE) of leaves.6、Effects of different exogenous hormones on stomatal limitation(Ls) and apparentmesophyll conductance（AMC）of isolated soybean leavesLsof four soybean cultivars were all higher than control with the treatment of ABA, whileAMC were lower than control. It suggested that stomatal limitation played a role in the declineof soybean Pnunder ABA treatment. The decline of AMC showed that Pndecreased was resultof stomotal limitation factor and non-stomotal limitation factor working together. From differentgrowth stages, Lswas highest at V4stage and lowest at R4stage, which suggested that stomotallimitation factor was weakest at R4stage. AMC was highest at R4stage, which showed that thisperiod was the most productive period to soybean growth. Lsof four soybean cultivars were alllower than control with the treatment of IAA and CTK, while AMC were higher than control. Itshowed that IAA and CTK can increase the photosynthetic rate of soybean and promote plantgrowth.This paper indicated that: there were difference in effects of different exogenous hormoneson soybean photosynthesis at different growth stages. CTK and IAA significantly promotedsoybean leaf photosynthesis at different growth stage, ABA significantly inhibited soybean leafphotosynthesis at different growth stage. |
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