| Livestock manure,as traditional organic fertilizer can increase nutrient elements such as nitrogen and phosphorus in soil,fortify organic matter content in soil,improve soil structure and promote the growth of crops when it is applied to the fields.The addition of trace elements(containing heavy metals)and the use of antibiotics are at a state of disorder on account of lacking of standardization in the process of livestock breeding in China.Most of heavy metal and antibiotics are discharged out of the animal body with the feces and urine,resulting in excessive heavy metals in manure.A large number of experiments have demonstrated that frequent application of pig manure to the field can lead to the accumulation of antibiotics,heavy metals and antibiotic resistance gene(ARGs)in the soil,what’s more,heavy metals and antibiotics can accumulate in crops and cause adverse effects on crop growth and food safety.Three kinds of soil(black soil,red clay and yellow soil),three kinds of additives(EDTA,chitosan and rice straw)were selected as objects of the study to explore the abundance of ARGs,changes and correlations of both nutrient elements and morphological distribution of Cu,Zn in the soil after pig manure was applied to the field.Finally,lead(Pb)and sulfamethoxazole(SMX)which present a higher concentration in the pig manure samples were chosen as objects of study to research the accumulation of Pb and SMX in hydroponic pepper and the joint toxicity to plant.The main research work and results are as follows:(1)Based on the experiment of three kinds of soil applying to the pig manure,its results reveal that oil properties significantly affect the attenuation of ARGs.After 90 days,the residual abundance of ARGs in three soils was like:black soil<red clay<yellow soil.We speculate that the rich organic matter content in the black soil reduced the selective pressure of heavy metals on the ARGs,and red clay with its stronger viscosity and low air permeability accelerated ARGs attenuation.The residual abundance of ARGs was lower in the soil layer of 10-20cm,and the proportion of lower abundance of ARGs was in the soil layer of 10-20cm was 71.3%after 90 days.Oxygen levels may explain this phenomenon.(2)The test in which pig manure was applied to field with different additives showed that EDTA significantly increased the content of exchangeable Cu and Zn in soil,especially in the 0-10cm soil layer.With the role of EDTA,the abundance of ARGs decreased slowly and that of sul2 and tetX increased under the co-selective pressure of high content of exchangeable heavy metals.Besides,EDTA also inhibits nitrification.Chitosan as a heavy metal chelating agent,accelerated the attenuation of ARGs abundance in the early period of manure application.However,the gradual decomposition of chitosan will lead to a series of consequences including the activation of Cu、Zn,the increase of nitrate nitrogen content,the quick decrease of active phosphorus in the soil after 16 days,which inhibited the attenuation of ARGs abundance.And as for the rice straw,it can obviously accelerate the attenuation of ARGs by means of increasing soil porosity,nitrate nitrogen content and microbial activity,and maintaining the exchangeable state and carbonate bound state of Cu and Zn.(3)The combined toxicity of SMX and Pb was antagonistic to hydroponic pepper by IBR value.SMX can reduce Pb2+ enrichment in hydroponic pepper by-NH2 functional group chelate Pb2+.On the contrary,Pb2+ can increase the enrichment of SMX in hydroponic pepper.Pb2+ is the main factor causing oxidative stress in hydroponic peppers.Exposure of hydroponic capsicum to pollutants in a short time will result in increasing SOD activity,GSH content and MDA content.Prolonged exposure will cause irreversible oxidative damage to capsicum. |
