Effects Of Galinsoga Parviflora Planting Density On Its Cadmium Accumulation Characteristics And The Safety Production Of Lactuca Sativa

This study adopted artificial simulating the field of common economic crops cultivation modes and cadmium pollution soil culture in pot experiment methods, used cadmium hyperaccumulator Galinsoga parviflora and leafy vegetable Lactuca sativa to be tested, under the cadmium pollution stress of 10mg·kg-1 set Galinsoga parviflora planting density as 1,2,3,4 and 5 plant·pot-1 to respectively mixed cropping with 1 plant·pot-1 planting density of Lactuca sativa, while single planting Galinsoga parviflora (1,2,3,4 and 5 plant·pot-1) and Lactuca sativa (1 plant·pot-1) as control (CK), researched the variation in the various processing the growth status, cadmium accumulation characteristics, nutrient uptake of two kinds of plants, the physiological and biochemical, quality indexes of Lactuca sativa, and the physical and chemical properties of rhizosphere. to discuss the regulation mechanism of the cadmium accumulation characteristics and nutritional quality of Lactuca sativa by the different planting pattern and density control, aimed at provided the theoretical reference to vegetables safety production of cadmium pollution farmland in Sichuan area, at the same time put forward the new method to solve the problem of its ecological restoration. The main results were as follows:(1) Under the cadmium stress, different density of Galinsoga parviflora mixed cropping with Lactuca saliva, two kinds of plants’ rhizosphere soil pH had decreased, resulted in the soil cation exchange capacity (CEC) and available cadmium content were increased, and then the effectiveness of soil available nutrients had been inhibited, but it had improved the available phosphorus content in the rhizosphere soil. It means that Galinsoga parviflora and Lactuca sativa strengthened the mutual allelopathy by the way of releasing the root exudates to change the various physical and chemical properties of rhizosphere soil, and make further influence for all the life activities of plants themselves. Ions activation of rhizosphere soil effect and the variation of the effectiveness of nutrient elements become the inner base of the cadmium accumulation characteristics of Galinsoga parviflora and safety production of Lactuca sativa.(2) Under the cadmium stress, the low density of mixed planting the Galinsoga parviflora had been conducive to the growth of the two kinds of plants, but Galinsoga parviflora planting density was too high will bring negative effects on the growth starus of the two plants. Research had shown that:the plant height, root length and biomass of Galinsoga parviflora decreased slowly in its planting density were 2～3 plant·pot-1, meanwhile the plant height, root length and biomass of Lactuca sativa increased significantly in it’s mixed cropping with Galinsoga parviflora as 1～2 plant·pot-1 density.(3) Under the cadmium stress, increase of planting density had led to the increase of each part of the Galinsoga parviflora’s cadmium content and the more density led to more increment. The low density as 1-3 plant·pot-1 mixed cropping with Galinsoga parviflora can reduce the absorption of cadmium in Lactuca saliva, while the Galinsoga parviflora’s planting density was 1 plant·pot-1, the cadmium content of Lactuca saliva’s edible part was reduced by 9.28% than single. In terms of repair capacity, mixed and planting density increased could improve the remediation efficiency of Galinsoga parviflora for cadmium contaminated farmland, at the same time bring down the cadmium accumulation in Lactuca sativa; mainly manifested that when Galinsoga parviflora planted 5 plant-pot-1, its cadmium accumulation content was largest as 0.870-1.069mg-kg-1, and relative remediation ability reached 2-level, the Lactuca sativa in mixed planting with Galinsoga parviflora as 1-3 plant-pot-1, its cadmium accumulation was less than single planting.(4) Under the cadmium stress, the increase of planning density of Galinsoga parviflora had suppressed its nutrient elements absorption except phosphorus, for Lactuca sativa, mixed cropping with Galinsoga parviflora in 1 plant-pot-1 density had raised its absorption of nitrogen and kalium, but Galinsoga parviflora’s planting density was too high would decreased all the nutrient elements accumulation in Lactuca sativa. Simultaneously, the total phosphorus content of Galinsoga parviflora increased with its increased planting density means that phosphorus elements played an important role on the detoxification of cadmium in Galinsoga parviflora.(5) Under the cadmium stress, mixed cropping of Galinsoga parviflora’s density increase had launched the antioxidant defense system of Lactuca sativa to resist the damage from reactive oxygen species (ROS) of Lactuca sativa in stress, on the other hand, it had reduced the utilization efficiency on the light energy of Lactuca sativa to lessened its photosynthesis and influenced plant’s physiological metabolism. Thereinto, the Lactuca sativa’s antioxidant protective enzymes system had maintained high and stable activity in mixed cropping of Galinsoga parviflora as 2-3 plant-pot-1 density, and its photosynthesis had showed that when Galinsoga parviflora mixed planting density were 1-2 plant-pot-1, the two plants’interspecific competition had little effect on the physiological metabolism of Lactuca sativa.(6) Under the cadmium stress, the mixed planting density control of Galinsoga parviflora caused certain influence to the quality of Lactuca saliva. With the mixed planting of Galinsoga parviflora density increased, the Lactuca sativa’s vitamin C and soluble protein content had reached the maximum value in mixed cropping with Galinsoga parviflora as 4 and 3 plant-pot-1 density, respectively 81.67μg·g-1 and 6.10mg·g-1; and its soluble sugar content in mixed planting 1 plant-pot-1 of Galinsoga parviflora had reached the maximum value as 7.35mg·g-1, after that it had tended to decline gradually, however the cellulose and nitrate content of Lactuca sativa showed a rising trend. Overall, the low density as 1-3 plant·pot-1 mixed planting with Galinsoga parviflora could promote the quality of Lactuca sativa in a certain extent.In conclusion, mixed planting the hyperaccumulator Galinsoga parviflora of low density as 1-3 plant·pot-1 with leafy vegetable Lactuca sativa could enhance the remediation efficiency of Galinsoga parviflora for cadmium contaminated farmland, at the same time ruduce the cadmium accumulation in Lactuca sativa, improve the yeild and quality of Lactuca sativa, and maintain Lactuca sativa at the ideal nutrition absorption and physiological metabolism level. Therefore, this study had provided a new method for vegetables safety production and ecological restoration of cadmium pollution farmland in Sichuan area.