Effects Of Four Antibiotics Single And Combined With Cu On Enzyme Activity And Microbial Community In Saline Soil Of The Yellow River Delta

As one of the main threats to soil health,soil salinization is considered to be an important factor affecting the distribution of soil fertility and biodiversity.The soil salinization in Yellow River Delta of China has spread from offshore to inland at an unprecedented rate,severely limiting the availability of soil nutrients and microbial activities.Organic fertilizer is a common means to control soil salinization,and the application of organic fertilizer will cause the residue of antibiotics and Cu and other heavy metals,so residual antibiotics and heavy metals will often be detected in saline soil.At present,there is little research on the impact of different types of antibiotics and copper on soil enzyme activity and microbial community structure of saline soil in Yellow River Delta.This study selected four antibiotics and heavy metal Cu to treat two types of saline soil(slight saline soil and moderate saline soil): Blank(CK),Chlortetracycline(CTC),Enrofloxacin(ENR),Sulfamethoxazole(SMZ),Tylosin(TYL),Copper(Cu),Chlortetracycline+Cu(CTC＿Cu),Enrofloxacin+Cu(ENR＿Cu),Sulfamethoxazole+Cu(SMZ＿Cu)and Tylosin+Cu(TYL＿Cu).The basic physical and chemical properties of topsoil and soil enzyme activities were measured,and soil microbial indicators were measured based on Illumina Mi Seq high-throughput sequencing technology.The results indicate that:(1)The addition of four antibiotics and Cu significantly decreased the activities of urease(URE),catalase(CAT),sucrase(SUC),and alkaline phosphatase(ALP)in the two saline soils.Among slight saline soil treatments,the combined treatment with enrofloxacin and Cu had the most significant inhibitory effect on soil URE activity;The combined treatment with tylosin and Cu had the most significant inhibition on CAT and SUC activities in soil;The combined treatment with chlortetracycline and Cu had the most significant inhibition on soil ALP activity.In moderate saline soil treatment,the combined treatment with tylosin and Cu had the highest inhibition of CAT and SUC activities in the soil;The combined treatment with sulfamethoxazole and Cu had the highest inhibition on soil URE and ALP activities.The enzyme activity of moderate saline soil was significantly lower than that of slight saline soil.(2)Four antibiotics and Cu treatment significantly altered the diversity and richness of bacteria and fungi in two saline soils.In the single treatment of slight saline soil,the addition of sulfamethoxazole had the lowest bacterial diversity,while the addition of tylosin had the lowest bacterial richness;The single treatment with the addition of tylosin had the lowest fungal diversity and richness;In the combination treatment of slight saline soil,the diversity and richness of bacteria and fungi were the lowest when sulfamethoxazole and Cu were added.In the single treatment of moderate saline soil,the addition of tylosin resulted in the lowest bacterial diversity and richness;The single treatment with the addition of sulfamethoxazole showed the lowest fungal diversity and richness;In the composite treatment,the addition of sulfamethoxazole and Cu resulted in the lowest diversity and richness of bacteria and fungi.(3)The OTU abundance and relative composition of bacterial communities in slight and moderate saline soil treatments were significantly different.The first dominant bacterial phylum was Proteus,and the single treatment adding tylosin had the most significant impact on the OTU abundance of bacterial communities in the two saline soils.The OTU abundance and relative composition of fungi in slight and moderate saline soil treatments were also significantly different.The first dominant fungal phylum in each treatment of the two saline soil treatments was Ascomycota,and the relative abundance was the lowest in the single treatment adding sulfamethoxazole.(4)The addition of four antibiotics and Cu significantly altered the bacterial and fungal community structure of two saline soils.The single treatment of tylosin and the combined treatment of chlortetracycline and Cu have the most significant effects on the bacterial community structure of slight saline soil;The single treatment of enrofloxacin and the combined treatment of chlortetracycline and Cu have the most significant effects on the bacterial community structure in moderate saline soil;At the phylum and class levels,the single or combined effects of four antibiotics with copper did not significantly affect the fungal community structure in slight saline soil;Compared to the composite treatment,the single treatment of four antibiotics had the most significant impact on the fungal community structure in moderate saline soil.(5)In slight saline soil,the bacterial community was significantly positively correlated with the three enzymes URE,CAT,and SUC,while the correlation with ALP was relatively low.Only two bacterial phyla were significantly negatively correlated with ALP;The bacterial community in moderate saline soil was significantly correlated with URE,CAT,and SUC,but not with ALP.Only URE and SUC enzymes were correlated with the fungal community in slight saline soil at the gate level,while CAT and ALP were not significantly correlated with the fungal community in slight saline soil at the gate level;The four enzyme activities were correlated with the fungal community in moderate saline soil at the phylum level,with the most significant correlation between URE and CAT and the fungal community in moderate saline soil.