Effects Of Veterinary Antibiotics Sulfamethazine On Factors Related To CH₄,N₂O And NH₃ Emissions In The Rice-wheat Croplands

Nowadays,human-induced climate change and soil pollution have become severe issues that threaten the health and survival of human beings,and have attracted wide attention from the domestic and foreign academic circles.CE4 and N2O are important components of greenhouse gases that contribute to climate change.Meanwhile,NH3 can also indirectly contribute to global warming through a series of chemical reactions that can produce nitrogen oxides.Farmland ecosystem is an important emission source of CH4,N2O and NH3.In recent years,with the development of intensive livestock farming,veterinary antibiotics usage continues to increase,resulting in severe soil antibiotic pollution which can change soil environment.Now,it’s gradually influencing the nutrient cycling of carbon and nitrogen in the soil,and in turn influencing the soil factors related to CH4,N2O emissions and NH3 volatilization,and give rise to the change of the gas emissions in the end.To explore the influence of veterinary antibiotics on associated factors of CH4,N2O emissions and NH3 volatilization under the condition of different types of basal fertilizer(compound fertilizer and pig manure),this paper selected the most widely used sulfamethazine(SMZ)which belonged to sulfonamides as research object and conducted two situ observation experiments in the rice-wheat croplands.There were ten treatments in the rice field experiment.The treatments were divided into two areas,the conventional transplanting of rice(RT)and the postpone transplanting of rice(RP),and each area was set with 5 treatments,including:no fertilizer and no antibiotics applied(RTCk,RPCK);the compound fertilizer used as basal fertilizer with and without the addition of SMZ(RTCF,RPCF,RTCF+SMZ30,RPCF+SMZ30),and the pig manure used as basal fertilizer with and without the addition of SMZ(RTCM,RPCM,RTCM+SMZ30,RPCM+SMZ30).The concentration of SMZ added was 30mg/kg.Nine treatments were set in the wheat experiment,including:no fertilizer and no antibiotics applied(WCK),compound fertilizer used as basal fertilizer,with the addition of 0,5,15,30mg/kg SMZ respectively(WCF,WCF+SMZ5,WCF+SMZ15,WCF+SMZ30),pig manure used as basal fertilizer,with the addition of 0,5,15,30mg/kg SMZ respectively(WCM WCM+SMZ59 WCM+SMZ15,WCM+SMZ30).Urea was applied as topdressing in the all fertilizing treatments.The results of field experiments showed that the crops,basal fertilizers(compound fertilizer and pig manure)and antibiotics dose all had obvious influence on the effect of SMZ on soil factors related to CH4,N20 and NH3 emissions.(1)Effects on factors related to CH4 emission in the rice field:In the treatment with compound fertilizer,RPCF+SMZ30 significantly increased soil DOC content first and then reduced it(P<0.05),while RTCF+SMZ30 had no significant effect on it(P>0.05).In the treatment with pig manure,RPCM+SMZ30 and RTCM+SMZ30 both mainly showed the promoting effect on soil DOC content.The effects of SMZ on soil CH4-16S rRNA mcrA and pmoA genes abundance of soil were as follows:SMZ significantly promoted their abundance(P<0.01),except for RTCF+SMZ30 which significantly inhibited their abundance(P<0.01),but the intensity of promotions was different.At the sametime,the results showed that in the whole observation period,CH4 emission rate was highly positively correlated with the Log value of soil mcrA gene abundance(P<0.01).In addition,with the conventional transplanting of rice,CH4 emission also was significantly positively correlated with soil NH4+-N,while with the postpone transplanting of rice,it significantly negatively correlated with the Log value of soil CH4-16S rRNA gene abundance(P<0.05);And according to the statistical analysis,the progressive linear regression equation of CH4 emission rate with associated factors was:FCH4=2.26mcrA+0.13NH4+-N-1.54pmoA-0.10WFPS+2.13(R2=0.495,P<0.05)during the period when CH4 emission was significantly affected by SMZ(6.18-9.6),indicating that mcrA and pmoA genes were the main driving factors of CH4 emission.(2)The effects on factors associated with N2O emission were as follows:During the rice season,the effect of different treatments with SMZ on soil NH4+-N and NO3--N content was different.Except that RPCM+SMZ30 significantly increased soil NH4+-N content(P<0.01),there was no significant difference in soil N14--N between the treatment with and without the addition of SMZ(P>0.05).But for the soil N03--N,there was no significant difference between RPCM+SMZ30 and RPCM(P>0.05),while RPCF+SMZ30 significantly increased the content of soil NO3--N(P<0.01),RTCF+SMZ30 and RTCM+SMZ30 both significantly decreased soil NO3--N content(P<0.01).The effects of SMZ on the abundance of soil AO A,AOB,nirK,nirS and nosZ genes were consistent with that of microbial genes associated with CH4 emission,which all of them mainly showed the activation effect,in addition to the RTCF+SMZ30 that significantly inhibited them.At the same time,during the whole observation period,N2O emission was only significantly positively correlated with the Log value of soil nirK gene abundance(P<0.05).During the wheat-growing season,under the condition of compound fertilizer,the low concentration of SMZ(5 mg/kg)significantly promoted soil NH4+-N content at the early stage of SMZ applied(P<0.05).Whereas,the medium(15 mg/kg)and high(30mg/kg)concentration of SMZ both had inhibitory effect on NH4+-N content,especially,the high concentration of SMZ significantly increased it(P<0.05).At the same time,the low,medium and high concentrations of SMZ all promoted soil NO3--N content.But under the condition of pig manure,only the medium concentration of SMZ highly significantly increased soil NH4+-N content at the early stage of SMZ applied(P<0.01).While for the soil NO3--N content,the low,medium and high concentrations of SMZ all showed the significantly inhibitory effect on it(P<0.01).What’s more,during the whole observation period,N2O emission was only positively correlated with soil NH4+-N content(P<0.01).(3)Effects on factors associated with NH3 volatilization were as follows:During the rice season,RPCM+SMZ30,RTCM+SMZ30 and RTCF+SMZ30 all significantly promoted urease activity,especially for the RTCM+SMZ30 treatment which achieved highly significant effect during the whole observation period(P<0.01).Whereas,there was no significantly correlated relation between NH3 volatilization rate and urease activity.But with the conventional transplanting of rice,NH3 volatilization was significantly positively correlated with NH4+-N content(P<0.05).During the wheat season,no matter what kinds of basal fertilizer were applied,the low,medium and high concentrations of SMZ all mainly showed inhibitory effects.And according to the correlation analysis,during the whole observation,NH3 volatilization was only significantly positively correlated with NO3--N content(P<0.01).But in the period when SMZ had significant effect on NH3 volatilization,namely the topdressing period,the time weighted average of NH3 volatilization rate was significantly positively correlated with the time weighted average of successively backwards urease activity(P<0.01).