| Cr???is a chemical element with high toxicity and high risk of pollution.When it reaches a certain concentration in the soil,it can produce strong toxic effects on soil microorganisms,plants and animals,and cause a series of human health problems through food chain or other channels.Leizhou Peninsula,a major producer of melon,vegetables and rice,located in the tropical north margin and subtropical monsoon climate zone,is affected by basalt,which has resulted in the latosols of the area having higher chromium levels,relatively higher than the whole of Guangdong province and China as a whole.Due to the high accumulation of heavy metals in leafy vegetables,there are major health concerns associated with the local product.Previous studies have confirmed that organic fertilizers can reduce the risk of heavy metal pollution in soil and alleviate the toxicity of heavy metals to soil microorganisms and plants.As an economic,effective and environment friendly remediation material for heavy metal pollution in soil,organic fertilizers have attracted extensive attention.Latosol is a ferrallitic and acidic soil.The environmental behavior of Cr???in latosol is different from that in other soils.Presently,the effects and mechanisms of organic fertilizers in reducing Cr???pollution in latosol are not clear.Similarly,how organic fertilizers affect the microbial biomass structure in laterite soil polluted by Cr???are also poorly understood.Therefore,the changes of Cr???morphological transformation,soil enzyme activity,microbial community structure and the growth status of red amaranth in the soil before and after the application of organic fertilizer into exogenous Cr???contaminated latosol were compared,and the related mechanisms were discussed.To understand the role of organic fertilizer in reducing Cr???pollution in latosol.The main findings of the study are as follows:?1?In the initial stage of contact between hexavalent chromium and latosol,the adsorption was dominant,and the reduction effect gradually increased in the latter stage.The application of organic fertilizers in the soil makes the Cr???reduction Cr?III?efficiency more obvious.?2?Without fertilization,the activity of urease,acid phosphatase,catalase and dehydrogenase decreased with the increase of Cr???concentration,and the activity of sucrase increased initially but decreased during pollution.The activities of urease,acid phosphatase,catalase and dehydrogenase all increased with the addition of organic fertilizer,and the activity of sucrase first decreased and then increased with time.The content of Cr???in water-soluble soil was negatively correlated with acid phosphatase and dehydrogenase,and negatively correlated with catalase and urease.?3?The main microbial Phylum of soil samples are Firmicutes,Actinobacteria,Chloroflexi,and Proteobacteria.Relative abundance of Actinomycetes,Chlorobacteria and Acidobacteria decreased as Cr???contamination increased.Organic fertilizer lead change for sample diversity and the abundance of most bacteria to varying degrees.The microbial community structure in the soil with 50 and 150 mg·kg-1Cr???concentration was significantly different before and after fertilization.There was a significant correlation between environmental factors and most bacteria.?4?The application of organic fertilizer lead to an increase in biomass,plant height and root length together with a decrease in concentration of chromium in the shoot and root.There was reduction in the physiological damage to red amaranth.The increase in organic fertilizer application decreased the fraction of exchangeable and carbonate bound species in the soil,promoting the transformation of Cr to organic bound and solid residual species.The results of the study showed that the application of organic fertilizer reduces the levels of Cr???in the primary laterite of basalt,improves the abundance and diversity of microbial communities in Cr???contaminated soils,alleviates the Cr???poisoning in crops and eventually reduce the chromium levels in agricultural products.This conclusion can provide a scientific basis for the treatment and remediation of Cr???contaminated soils from the basalt parent material of the Leizhou Peninsula. |
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