Mechanistic Study On The Regulation Of Photosynthesis And Transport Of Carbon Assimilation Products In Soybean By Foliar Applied Iron-based Nanomaterials

Iron as a necessary nutrient element has many important functions in plant growth and development such as involvement in the biosynthesis of respiration and improves the performance of photosystems.Iron-based nanomaterials with unique physicochemical properties are exhibiting potential to improve crop productivity,which enable their potential application in agricultural sector.The soybean is widely cultivated as a cash crop in China.Soybean（Glycine max L.）demands high levels of iron due to its inclusion in the compositions of leghemoglobin,nitrogenase,and cytochromes.Whether iron-based nanomaterials can promote plant growth,the potential mechanism and the effect of iron-based nanomaterials and ordinary iron fertilizer remain to be further verified.In order to better understand the effect of iron-based nanomaterials（NMs）on the soybean growth and its related mechanisms,different concentrations(0,1,10 and 50 mg·L^-1)of Fe₃O₄ NMs were sprayed on the leaf of soybean at three different stages（seedling,flowering and mature）,which cultured in soil conditions.All the treatments in level of 10mg·L^-1 exhibited the best performance for soybean growth.Then,under the optimal application concentration,the effects and mechanism of Fe₃O₄ NMs and Fe-EDTA on soybean growth and sucrose transport were compared.The results are as follows:（1）Foliar applied different concentrations of Fe₃O₄ NMs could significantly promote the fresh weight,root length,number of root tips and root volume of soybean at seedling stage,and the promotion effect increased initially and decreased afterwards with the increasing of applied Fe₃O₄ NMs concentration.10 mg·L^-1 was the best concentration of Fe₃O₄ NMs to promote soybean growth,and the promoting effect of Fe₃O₄ NMs in different treatment groups was greater than that of chelated iron fertilizer(equal Fe content to 10 mg·L^-1Fe₃O₄NMs).Under Fe₃O₄ NMs treatment,seedling soybean photosynthetic rate increased by 22.7%,transpiration rate,stomatal conductance and intercellular CO₂ concentrations were significantly higher than those under Fe-EDTA treatment.Fe₃O₄ NMs increased the sucrose transport to the root（sink）,increased the sink source ratio at the seedling stage,and promoted the absorption of nutrients in the root by up-regulating the sucrose transporter genes（Gm SWEET 6,Gm SWEET 15,Gm SUT 2）in the leaves and roots.（2）Foliar applied different concentrations of Fe₃O₄ NMs could significantly promote the shoot fresh weight,root-shoot ratio,flower fresh weight of soybean at flowering stage.10mg·L^-1 was the best concentration of Fe₃O₄ NMs to promote flowering soybean growth,and the promoting effect of Fe₃O₄ NMs in different treatment groups was greater than that of chelated iron fertilizer(equal Fe content to 10 mg·L^-1Fe₃O₄ NMs).In Fe₃O₄ NMs processing under flowering soybean photosynthetic rate than Fe-EDTA treatment group increased by45.5%,the increase in photosynthesis is the synthesis of photosynthetic product,at the same time Fe₃O₄ NMs promoted the absorption of nutrients in the flower and root（sink）by up-regulating the sucrose transporter genes（Gm SWEET 6,Gm SWEET 15,Gm SUT 2）,it could improved sucrose transport efficiency,promote the growth of soybean.（3）Foliar applied different concentrations of Fe₃O₄ NMs could significantly promote the plant height,shoot fresh weight and single plant fresh weight of soybean at mature stage,and10 mg·L^-1 Fe₃O₄ NMs was the best spraying concentration,and the effect was better than that of Fe-EDTA.Fe content in different parts of soybean plant（leaf,root and bean）at mature stage was significantly increased under 10 mg·L^-1 Fe₃O₄ NMs treatment.The iron content in soybean leaf,root,and soybean grains after exposed 10 mg·L^-1 Fe₃O₄ NMs was 1.14,1.19,and 1.36 fold respectively.Fe₃O₄ NMs also promoted the up-regulation of net photosynthetic rate of soybean at maturity stage,up-regulated sucrose transporter genes（Gm SWEET 6,Gm SWEET 15,Gm SUT 2）in leaves and beans,improved the transport efficiency of sucrose to beans（sink）,increased the sink source ratio at maturity stage,and promoted number of soybean grains at maturity stage.（4）Foliar applied different concentrations of Fe₃O₄ NMs could significantly promote the contents of vitamin C,mineral elements and total protein in soybean grains,and the nutritional quality of soybean grains was improved.In conclusion,foliar application iron-nanofertilizer（Fe₃O₄ NMs）promoted the growth and nutrient uptake of crop,the transport efficiency of photosynthate to the target reservoir in different periods,promote the growth of soybean more pertinently,and improve the nutritional quality of soybean grains.