Effect Of Application Of Ferrihydrite On Growth And Antioxidative Enzyme Activities Of Maize And Rice

Iron is one of the necessary microelements for plant growth.Some nano-scale iron oxides not only play the role of the nutrition carrier with the advantages of small size,large specific surface area,but also as iron supplement improve plant iron deficiency symptoms as previous research suggested.At present,however,the impact of ferrihydrite on plant physiology is little known.Hydroponic and soil experiments in this paper were aimed to study the effect of external addition of ferrihydrite on the growth and antioxidative enzyme activities of maize and rice.The main results are as follows:X-ray diffractometry and scanning electron microscope analysis showed that the laboratorial synthesized ferrihydrite,with particle size between 2-7 nm,is typical 2-line ferrihydrite.Particles of the solid material were amorphous aggregates,while these in liquid were transparently suspended colloids in nutrient solutions when its concentration was at low levels.The seed germination experiment results showed that the germination index,the vigor index and the average root length of maize increased significantly by 38.3%,62.0%and 53.9%,respectively,and the average germination time was reduced by 56.6%,when the concentration of ferrihydrite was 20 mg/L as compared with water(CK1).Similarly,the germination index,vigor index and average root length of rice increased significantly by 21.6%,45.5%and 9.4%,respectively,as compared with CK1,when the concentration of ferrihydrite was 10 mg/L.The maize seedling growth experiment results showed that the fresh weight of shoot,root of length and chlorophyll content increased significantly by 15.4%?10.0%and 24.9%as compared with the no-iron control(CK2),when the concentration of ferrihydrite was 20 mg/L.Concentration higher than 50 mg/L had damaged maize growth.Ferrihydrite concentrations of no more than 20 mg/L increased POD and CAT activities in maize leaves.However,the concentrations of more than 20 mg/L led to the gradual reduction of POD and CAT activities.In addition,results of leaf Fe determination and transmission electron microscopy observation showed that ferrihydrite at the concentration of 10 mg/L could enter the root cells of maize and significantly increased the content of iron in shoot by 75.1%as compared with CK2.However,higher ferrihydrite concentration of more than 20 mg/L resulted in the plasmolysis of root cell.The hydroponic rice seedling growth experiment results showed that the root of length,fresh weight of shoot,increased significantly by 32.1%and 19.5%,81.7%and 55.8%,as compared with the no-iron control(CK2),and chlorophyll content were 7.46 and 4.80 times higher than CK2,when concentration of ferrihydrite was 10 mg/L and 20 mg/L,respectively.The soluble protein content in rice leaves was 2.24 times of CK2,when concentration of ferrihydrite was 10 mg/L.The activities of SOD,POD and CAT in rice root was enhanced,while the activities of SOD and POD in the leaves increased when the concentration was 20-200 mg/L.In contrast,the activities of the antioxidant enzymes both in rice leaf and root cells decreased significantly when the ferrihydrite concentration was 500 mg/L.In addition,results of leaf Fe determination and transmission electron microscopy observation showed that ferrihydrite was observed in intercellular space and traveled along the cell wall when rice was treated with 20-200 mg/L of ferrihysrite.The iron content in the aerial part of rice increased by 42.9%and 41.1%,respectively,as compared with CK2,when concentration of ferrihydrite was 10 mg/L and 20 mg/L.However,when the ferrihydrite concentration was higher than 200 mg/L,no ferrihydrite particles in the root cells and intercellular space was observed.The promoting effect of ferrihydrite on seed germination and growth of hydroponic maize and rice seedlings suggested that low lever ferrihydrite benefit to hydroponic maize and rice seed germination and plant growth,whereas high concentrations of ferrihydrite damaged hydroponic maize and rice growth.A soil maize pot-experiment was also conducted with foliar spraying 0.5%of urea solution(U),0.5%a bacterial fermented lipopeptide solution(P)and 0.5%of an amino acid hydrolysate solution(A)and their corresponding solutions each with 100 mg/L of ferrihydrite,i.e.,UF,PF and AF,respectively.The results showed that the treatments UG,PG and AG increased the maize heights by 12.2%,19.4%and 17.1%,the root dry weights by 18.9%,13.2%and 6.5%,shoot dry weights by 45.5%,34.8%and 36.7%,as compared with U,P and A,respectively.As compared with U and P,UG and PG significantly increased the values of SPAD by 7.3%and 5.3%,respectively.UF,PF and AF significantly increased the soluble protein content in leaves,which was 3.95,1.44 and 1.22 times that of U,P and A,respectively.The total iron contents in the leaves by 58.9%,72.6%and 89.1%,as compared with the treatment U,P and A,respectively.Thus,the experiment suggested that foliar spraying fertilizers containing ferrihydrite significantly promoted maize growth and the accumulation of beneficial substances in maize leaves.