| Alternative planting is an important technical approach to the safe use of high-risk arsenic farmland.In recent years,there has been considerable controversy regarding the arsenic cumulative risk in maize and its suitability for alternative cultivation in high-risk arsenic farmland.Correctly understanding the difference in the cumulative risk of arsenic among maize varieties,and clarifying the mechanism of maize's absorption and tolerance of arsenic,could provide theoretical and practical support for cultivating maize as a low-absorption crop to carry out alternative cultivation in high-risk arsenic farmland in the future.The thesis took maize varieties widely planted in arsenic high-risk agricultural areas as an object,analyzed the differences in arsenic enrichment ability among maize varieties,and explored the principals of the absorption and the detoxification of arsenic by maize.The main results are as follows:1.Through field experiments,field surveys and literature retrieval at home and abroad,it has been shown that maize seeds have a low accumulation capacity of arsenic,which was far lower than the relevant standards required by China,Switzerland,Australia and WHO,and was an economic crop suitable for spreading and planting in arsenic-contaminated areas.However,there were differences in the accumulation capacity of arsenic among different maize varieties.In comparison,sweet maize had a higher accumulation capacity of arsenic.Common maize and waxy maize were the first choices of maize cultivar for planting in arsenic-contaminated areas.The arsenic content of different parts of maize was different.The order of arsenic content in each part of 18 maize varieties was: root > stem and leaf >grain,of which the arsenic content in root was 2.39 ~ 79.94 times of that in stem and leaf,and 69.52 ~693.70 times of that in grain.A stepwise regression model was used to obtain the quantitative relationship between maize arsenic absorption and transport coefficients affecting grain arsenic accumulation,which indicated that root fixation of arsenic and low ability to transfer arsenic to grain may be an important reason for low maize arsenic absorption.The contents of manganese,iron,sulfur,calcium and arsenic in maize root tip meristems were significantly positively correlated,which suggested that these elements may play an important role in arsenic retention in maize roots.2.Indoor hydroponic experiments showed that with the increase of arsenic concentration in the environment,the arsenic absorption of normal maize(N-506),sweet maize(S-MY)and waxy maize(W-23)increased significantly.It was found that the maximum arsenic absorption rate of N-506 was highest,which was 19998.62 mg/(kg·h)Fw,through fitting Michaelis-Menten equation.The time absorption kinetics experiment showed that when the arsenic concentration was 4 mg/L,the order of arsenic absorption ability among maize varieties was S-MY > N-506 > W-23.Arsenic in maize root table was significantly correlated with iron and manganese(P < 0.05),which indicated that the enrichment of iron and manganese in the root table was conducive to blocking the entry of arsenic into the root.Using the X-ray microfluorescence by synchrotron radiation(SR-?XRF)scanning micro-area,it was found that arsenic in the maize root tip meristem cross section was mainly distributed in the outerepidermis and middle column of maize root tip,and there were differences among maize varieties.3.Indoor cultivation experiments showed that when the environmental arsenic concentration was 0~ 36 mg/L,it showed that S-MY had stronger tolerance than W-23 and N-506,and its germination rate did not change significantly.And the arsenic concentration of S-MY that inhibited its biomass was the highest.As the arsenic concentration increased,the activities of superoxide dismutase(SOD)and peroxidases(POD)of each maize variety showed a downward trend.When the arsenic concentration was 12 and 4 ~ 20 mg/L,the catalase(CAT)activity of W-23 and S-MY was significantly higher than that of the control,which showed that the increase of CAT activity at that concentration is beneficial to reduce the hydrogen peroxide stress in the plant.Under arsenic stress,the nonprotein sulfhydryl groups(NPT)content in the roots of W-23 increased significantly.When the arsenic concentrations were 12 and 20 mg/L,the content of glutathione(GSH)and phytochelatin(PCs)both in S-MY and N-506 increased significantly,which indicated that non-protein sulfur-based substances in maize can detoxify arsenic by complexing with arsenic. |
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