Studying The Mechanism Of Selenium Nanoparticles Improving The Yield And Quality Of Leafy Vegetable Crops

The control technology of nano-agriculture has become the focus of environmental research because of its remarkable control effect on improving crop yield and quality,reducing resource input and reducing agricultural environmental pollution.However,due to the complexity of environmental systems and their own properties,many environmental processes and mechanisms of nanoparticles（NPs）in agricultural ecosystems are still unclear.Selenium nanoparticles（Se NPs）are expected to replace traditional Se fertilizer and play a role in agricultural production due to their low toxicity and high biological activity.Therefore,understanding the mechanism and process of Se NPs in agricultural ecosystem is conducive to the establishment of green and efficient Se-enrichment nanotechnology and the improvement of human health.This study with leafy vegetables crops（Brassica chinensis L.and lettuce）as the research object,with Se NPs as the application of material,through microcosmic and field experiments,the optimal culture system for Se NPs to improve the yield of leafy vegetable crops was constructed,the key process and mechanism of Se NPs to regulate their own bioavailability,photosynthesis and yield of leafy vegetable crops were clarified,and the Se-enrichment scheme of leafy vegetable crops was explored.The main results are as follows:（1）Se NPs at a certain concentration(≤0.5 mg·kg^-1)could play its own advantages in promoting the growth of crops（Brassica chinensis L.）and enriching the Se content of crops.Compared with sodium selenite,Se NPs(0.5 mg·kg^-1)had a better Se-enrichment effect(31.95μg·100g^-1dry weight).Se NPs increased the content of chlorophyll a（16.7%）and chlorophyll b（18.9%）and chloroplast electron transfer rate（27.4%）,which increased the net photosynthetic rate by 16.7%and promoted carbohydrate accumulation（15.6%）.By stimulating root secretion（betaine,proline,glycine,leucine and indole-3-acrylic acid,etc.）of the discharge and recruiting beneficial microorganisms（Pseudomonas and Bacillus,etc.）,Se NPs could improve the soil nutrient availability and the root growth of crop,eventually increase crop nutrient absorption capacity,further increase crop yields.（2）Reducing the application amount of Se NPs(0.05 mg·kg^-1)and changing the surface properties,it was found that Se NPs with different electric charges had different Se-enrichment effects on crops（Brassica chinensis L.）.Firstly,due to the negative charge of plant cell walls,negatively charged Se NPs（Se（-））were more likely to enter crops and transport upward,and stimulate the production of root exudates（citric acid,malic acid and tartaric acid）,increase the amount of negative charge on soil surface,and further improve the mobility of Se（-）in soil.Secondly,the increase of organic acids increased the abundance level of beneficial microorganisms（Pseudomonas and Bacillus,etc.）in the rhizosphere,further affected the bioavailability of Se NPs,and improved the Se-enrichment efficiency of crops(27.07μg·100g^-1dry weight).Se NPs could improve the nutritional quality of crops（amino acids,flavonoids,fatty acids and TCA acids）and promote the synthesis and accumulation of ascorbic acid（Vc）in vivo by regulating the gene levels（PMI,PMM,VTC1,GME,VTC2,VTC4,L-GDH and L-GLDH）.（3）Through studying the effect of Se NPs on growth promotion and Se-enrichment of Brassica chinensis L.and lettuce in farmland ecological environment,it was found that Se NPs have universality and feasibility in farmland application.In addition to increasing the relative abundance of amino acids,flavonoids,fatty acids and TCA compounds,field application of Se NPs significantly increased the levels of salicylic acid（55.3%）and jasmone（104.2%）in crops compared with pot experiment,making crops more adaptable to the ecological environment in the field.More importantly,compared with sodium selenite,the application of Se NPs could reduce soil Se residues and improve the economic returns of crops.