Regulation Of Selenium And Zinc On Growth And Quality Of Alfalfa And Its Mechanisms

Selenium (Se) and Zinc (Zn) are two kinds of important essential micronutrient for many organisms,including plants, animals and humans. Se is the protestant of life, which has triple biological functionsincluding nutrition, toxicity and detoxification. Meanwhile, it has been proved that suitable Se could notonly promote plant growth, increase crop yield and quality, but also enhance the antioxidative function andthe resistance to heavy metals. Zn is one of the important elements in the human body to maintain normaldevelopment, which participates in the synthesis of proteins and nucleic acids. Too much or too littlecontent of Zn would lead to physiological diseases; Similarly, Zn also has important biological functions inplants. Thus, a moderate amount absorption of Se and Zn for plants, animals and human have very importantsignificances.Alfalfa (Medicaco sativa L.), a high-class perennial legume forage plant due to its high yield and goodquality, is widely planted in Henan Province and the present planted area of alfalfa in Henan Province hasreached to159,000ha. And the planting area of alfalfa is rapidly expanding in recently years. It is a kindof high quality feed resource that showed moderate sensitivity to Zn deficiency and has strong ability toenrich Se, and the enriched Se in plants mainly exists in the organic Se form. Therefore, it is a direct sourceof animal and human intake of Se and Zn. In China, Se deficiencies in soils prevalently exist in the2/3areaand often result in the lack of Se in animal forage and human food. Zn deficiency has become an importantlimiting factor in sustainable crop production. Se and Zn deficiency is an important limiting factor insustainable crop production and is a factor often overlooked in determining the benefits and overall successof alfalfa pastures in rotations, especially in the Calcareous Fluvo-aquic soil, which is widely distributed inHenan Province. Se and Zn deficiencies not only affect crop yields, but also cause Se and Zn deficienciesof agricultural products, sequentially affect human health. Thus, it is very important to improve thebioavailability of Se and Zn to meet the needs of human beings and animals. In this paper, a series fieldexperiments were conducted to investigate the multiple effects of Se (applied as Na2SeO3) and Zn (appliedas ZnSO4·7H2O) on alfalfa growth, herbage yield and quality, protection-enzyme activity, the nutrientcomponents and amino acids formation contents, and on the soil fertility, soil enzyme activities and soilmicrobial biomass C and N, etc. The main results are as follows:1. A pot experiment was conducted to investigate the yield and quality of alfalfa by Se and Zncombined basal application in alfalfa grassland at ZhongMu Town in Zhengzhou City.(1) All the fertilization treatments had significant effects on the yield of alfalfa, and the effectiveness of Se was better than that of Zn, the Se and Zn combined basal application was the best. When applicationrates of Na2Se2O3was1.00mg/kg soil and ZnSO4·7H2O was0.442g/kg soil, Se-Zn combined fertilizershad the best application effects on forage production.(2) Se and Zn are essential elements for animals, and their contents are very important to satisfy thenutrient demands of animals and vital indices to describe the quality of herbage. Alfalfa had strongercapacities to absorb, transfer and utilize Se and Zn from soil to plant root. Thus, Se content andaccumulation in herbage, both underground part and aboveground part was significantly increased (P <0.05), the latter was about20times of the former, and the more Se in soil, the more Se in roots. Meanwhile,high-zinc promotes absorption to low-selenium and inhibits high-selenium in root. Zn content andaccumulation in herbage were also significantly increased, and inhibited by high-selenium. And applyingSe–Zn fertilizer promoted the absorption of N, P and K in alfalfa.(3) The amino acids content and formations is markedly increased by Se and Zn application. Thehighest total amino-acids (TAA) and total essential amino-acids (EAA) was occurred in the Se1Zn1treatment and Se1Zn2(Na2Se2O3was1.00mg/kg soil and ZnSO4·7H2O was1.769g/kg soil) treatment,respectively. While, the Se2Zn2treatment (Na2Se2O3was6.00mg/kg soil and ZnSO4·7H2O was1.769g/kgsoil) lower markedly the TAA and EAA content. Sulfur amino acids are limited amino acids in alltreatments. The EAAI value of alfalfa to Cattle Meat, Rabbit Meat and Goat Meat ranged from0.885~0.913,0.862~0.889and0.891~0.919, respectively. By analyzing the amino acid characteristics andnutritive value of forages, a better understanding of alfalfa plays an important role in yield and quality ofCattle, Rabbit and Goat.(4) Applied Se and Zn micronutrient fertilizer could significantly increase the content of availableselenium and DTPA-zinc, and they increased with the Se and Zn application ratios increased. With differentSe and Zn application ratios, the effect of Zn application ratio on Se availability showed different laws, andunder the condition of the same Zn application ratio, combined with Se could not significantly increased Znavailability.2. A field experiment was conducted to study the Se, Zn and fulvic acid (FA) combined application onalfalfa yield, quality and antioxidant enzyme activity through all fertilizer was applied as basal fertilizer.The results showed that:(1) Appropriate Se-Zn or FA applied could significantly increase herbage yield of alfalfa, and thehighest herbage yield was occurred in Se-Zn and FA combined application treatment. Applying Se-Zn orFA all could significantly increase the alfalfa Se and Zn content and accumulation. Se-Zn and FA combinedapplication could significantly increase alfalfa crude protein and crude ash content, but there was nosignificantly effect on crude fat, crude fiber and non-nitrogen extract content. Se-Zn and FA combinedapplication could also increase the contents of total anima acids (TAA) content and Val, Leu, Lys content and Asp, Arg, His, Tyr content, but there was no significantly effects on other amino acid.(2) The GSH-Px, POD and CAT activities in leaves of Se-Zn and FA combined applied treatment wasmaximum, and the SOD activity was minimum, it can say Se-Zn and FA combined applied could enhancealfalfa oxidation resistance. Se-Zn could markedly improve the activities of GSH-Px and CAT, anddecrease the activity of SOD and MDA, but have no significantly effect on POD; The FA couldsignificantly enhance GSH-Px, SOD and POD activities. At the same time, single applied Se-Zn or FA allcould increase the yield of alfalfa, and the effect of Se-Zn treatment was better than that of FA treatment.In conclusion, with nitrogen, phosphorus and potassium sufficiently supplied, Se and Zn or FA appliedcould enhance the protection enzyme activities in alfalfa and increase herbage yield, and amino acidsformation contents of alfalfa and it also favor high quality production. Se-Zn and FA combined applicationwas the best treatment.3. A pool-culture experiment was carried out by cultivating alfalfa with different fertilizer rates insandy, loamy and clayey texture of Chao soil, and investigated the effects of different texture of Chao soilon alfalfa growth, quality and amino acids content and formations, and also studid on the transformation ofSe fractions and the soil enzyme activities in the three soil textures.(1) Compared with different varieties under the different soil texture in the same cutting time withsame treatments, the dry matter (DM) herbage yield showed loam> clay> sand. As alfalfa growth, cuttingtimes had significant effect on DM herbage yield, the yield of the first cutting was the highest, then thesecond, the third was the lowest. Appropriate Se-Zn or FA applied could significantly increase herbageyield of alfalfa with three soil textures, and the highest herbage yield was occurred in Se-Zn and FAcombined application treatment. The ratio of dry to fresh weight of alfalfa in sandy soil was the lowest, butsoil textures had less apparent effects on the plant height, ratio of stem/leaf.(2) When alfalfa was planted in sandy soil, it had the highest crude protein content and the lowestcrude fat content, but there was no significantly effect on crude ash, acid detergent fiber and non-nitrogenextract content. Compared with different varieties under the same soil texture during the three cutting times,the crude ash of the first cutting was the highest than that of the others, while the crude fat and crudeprotein of the second cutting was the lowest; the third cutting had the highest acid detergent fiber and thelowest non-nitrogen extract content. Se-Zn and FA combined application treatment could remarkablyincrease the content of alfalfa crude protein and decrease the non-nitrogen extract content.(3) Among the contents of the17kinds of amino acid, alfalfa had higher contents of Asp, Glu and Leu,but lower contents of Met and Cys. Compaired with three kinds of soil textures, the highest EAA contentwere observed in sandy soil, the lowest EAA content was occurred in clay soil. Moreover, the contents ofTAA and EAA in NPK+FA+Zn+Se treatment reached to the maximum under the three soil textures, andlower markedly in NPK+Se+Zn treatment in sandy and loam soil. The contents of TAA reduced drastically in sandy soil, while it rapidly increased in NPK+FA+Zn+Se treatment in clay soil.(4) The SOD, POD and CAT activities in leaves was gradually increased with the increase of cuttingtimes. Alfalfa has the highest activity of SOD in loam soil, and the lowest POD and CAT activities in sandysoil. NPK+FA+Zn+Se treatment significantly increased (P <0.05) the activities of SOD in sandy soil andloam soil, and the largest SOD was occurred in NPK+FA treatment in clay soil. Meanwhile,NPK+FA+Se+Zn treatment had the largest POD in leaves in three soil textures.(5) A sequential extraction procedure for Se of different forms in soil was used．By the procedure，organic compound Se was the dominant Se fraction in the three soil textures, then acid soluble Se(carbonate-bound Se and manganese oxides-bound Se) was the second, they accounted for60.94%~69.91%of the total Se. Exchangeable Se was generally higher than residual Se, Water soluble Se was thelowest. Compared with three soil textures, water soluble Se was the highest in sandy soil than that of inloam soil and clay soil. Exchangeable Se content showed that: loam> clay> sand. Acid soluble Se washigher in loam soil, while, the organic Se and residual Se content were showed that: clay> loam> sand.These incidated that the less clay content in soil, Se bioavalability was higher.(6) The activities of soil catalase and urease in clay, and the alkaline phosphatase in loam were thehighest, while in sand soil were the lowest. Moreover, NPK+FA+Zn+Se treatment markedly increased theactivities of soil enzymes in three soil textures.The results also indicated that soil microbial biomass carbon (C) and nitrogen (N) were remarkablyinfluenced by fertilization. Soil microbial biomass C increased to the highest value in NPK+FA+Zn+Setreatment in three soil textures, the same as microbial biomass N except in NPK+FA treatment in loam soil.