| Soil is the indispensable environment for human survival and important resource for agriculture development. Food and environment problems facing the world are all closely related to soil and nowadays it is threatened by many factors, among which heavy metal pollution are the most serious one. In this study, soil-plant as an associated system. An integrated study method was accepted in this study, it includes ecological, geographical science, plant ecology, and also includes the experimental analysis, planting test and simulating test. The pollution of heavy metals on agricultural land in HaiNan. The research results provide scientific basis for optimization of development, farmland-use and pollution control of HaiNan. This study includes the following three correlative parts and summarizes the following results and conclusions.1 Pollution Status and contamination evaluation of heavy metals on farm land in Hainan IslandGeographical information system (GIS) combined with Geostatistics was applied to reveal the features of the spatial distribution of concentrations of heavy metal Hg, Cd, Pb, As and Cr on farm land in Hainan island. The results show that the average concentrations of the five metals are below the GradeⅡstandard of National environmental quality standard for soil (GB15618-1995), but the max contents of Hg,Cd,Cr were higher than the soil environmental quality standard, the concentrations of Hg,Cd,Cr were 1.63,0.64, and 586.70mg·kg-1.The theoretical semivariogram models of soil Hg, Cd, Cr and Pb fit for the Exponential model well. The spatial correlation of Hg and that of Pb are both weak, indicating that their concentrations are affected deeply by soil formation facts. The theoretical semivariogram model of soil As fits the Gaussian model well. The distribution spatial correlation of Cd, Cr and As is moderate respectly, indicting their concentrations are affected by the inputs from outside. The contour distrubition maps of the 5 heavy metals on farm land in Hainan island are obtained based on Kriging algorithm, showing that the heavy metal polutions caused by the inputs from outsides in industrial zones are most serious in Hainan island. Soil organic matter contents,pH and heavy metal contents of agriculture soils in Hainan were studied for relationships between soil organic matter content,pH and contents of soil heavy metals. Results showed that almost all the soil samples collected from Hainan Area organic matter contents were at middle or low levels with an average content of organic matter being 22.99%, but three parameters did vary much from site to site; an average pH value being 5.20. The results of correlation analysis showed that relationships between soil heavy metals and soil organic matter contents and pH were complicated.2 Pollution Status and contamination evaluation of heavy metals in orchards and vegetable gardens soil of Sanya CityVegetable security is important to our life, and it is absolutely necessary to set up city outskirt biogeocenose system. With industry and agriculture development, atmosphere, water and soil are getting more polluted. So vegetable is polluted in some degree. We measured and analyzed contents of heavy metals in vegetables and fruits and soils in Sanya of Hainan province. Heavy metal contamination condition of surface soil in orchards and vegetable gardens of Sanya City was evaluated by filed survey and sampling and by using standard comparison and Geoaccumulation index method. Result showed that the average values of the five heavy metals i.e., Hg, Cd, Cr, Pb and As, were all below GradeⅡof National environment quality standard (GB15618-1995). The variation coefficient of Cr,Hg,Pb and As were all> 1, which showed the distribution of four heavy metals were extremely uneven. However, the average values of Hg, Cd and Pb are higher than the background values of farm land in Hainan Island, showing slight pollution in certain areas. The spatial distribution of the five heavy metals were also obtained using Kriging algorithm approach, the spatial variation of soil pollution was obvious. The study provided guidance for sustainable development and utilization of orchards and vegetable gardens in Sanya city. Different evaluation methods and assessment standards of heavy metals were also used for comparison. Single factor pollution and comprehensive pollution index by national vegetable environmental quality standards and then evaluated by Nemero index, then analyzed the pollution source. The results showed that: mean concentrations of heavy metals in vegetables and fruits were not exceeded their corresponding natural-background values, no significant heavy metal pollution occurred in the study area as a whole. The enrichment of heavy metals in vegetables and fruits differed with their different physiological characteristics, growth time and sensitive degree to contamination, which comprehensive pollution index is green-leaves>Beans>melons> Rhizomas>Eggplants>fruits. Green-leaves were found slightly polluted, comprehensive pollution index is 1.19. Others comprehensive pollution index were less than 1.3 The response differences of different rice varieties in response to cadmium stress Cadmium(Cd)is important contaminants in agricultural soil and threatening agriculture and human health. With the development of industry and agriculture, the soil heavy metal cadmium pollution becomes more and more serious. In this study, two high-yielding rice cultivars currently used in the local production, Boyou 225, Short glutinous, A pot experiment with two Oryza sativa varieties in a paddy soil treated with five levels of cadmium was conducted to studied. Results showed that cadmium was not distributed uniformly in each part of rice plants. most of the absorbed Cd assembled in the root, the upper, the less, i.e. the law of distribution of Cd in different organs of rice should be:root> stem> rice husk> kernels. In rice roots and stems and leaves, cadmium is mainly distributed in the cell wall. Soluble components of cells, cell distribution of low cadmium. That is, F1 (Cell wall)> F3 (soluble part)> F2 (cell organelles and membrane part). Boyou 225 and short glutinous rice at low concentration under the deal with the accumulation of extractable Cd to sodium chloride, hydrochloric acid extractable, acid extractable mainly the three accounted for more than 80% of the total. With the increased concentration of Cd treatment, with short glutinous rice Boyou 225 extractable relative content of sodium chloride to reduce its absolute concentration close to saturation, and acetic acid extractable Cd increased relative content. Boyou 225 and short glutinous rice as compared to 80% alcohol extractable Cd and the residual proportion of the total are no significant changes.A pot experiment with two Oryza sativa Linnaeus varieties in a paddy soil treated with three levels of cadmium was conducted to study the physiological and biochemical and antioxidant enzyme system of the leaves. The results showed that with the increasing Cd concentration in soil increased the contents of malondialdehyde (MDA) and proline, which would be more pronounced in the Boyou225 than Short glutinous. The activities of SOD and POD were increased with the increased concentration of Cd, while the activities of catalase (CAT) were decreased. The activities of SOD and POD in the Boyou225 were significantly higher than those in the Short glutinous under relative higher Cd treatment. Our results indicated that with the Cd concentration increased caused the cell membrane. The rice varieties exhibited the genetic character on the Cadmium accumulation. The Cadmium contents of the grains increased with the increasing Cd concentration in soil. According to the state limit of cadmium in rice, the standard (GB 2762-2005), Content≤0.2 mg·kg-1. In this study, tropical paddy soil total Cd threshold were Boyou225 (Cd total)= 2.0 mg·kg-1; Short glutinous (Cd total)= 3.1 mg·kg-1. Therefore, for reducing the risk of the humanity to heavy metal, the rice varieties with the low capability of accumulating heavy metal in grains could be planted in a polluted soil. |
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