Aims Natural 15N abundance provides integrated information about nitrogen(N)input,transformation and output,indirectly reflecting N cycling traits within terrestrial ecosystems.However,relationships between natural 15...Aims Natural 15N abundance provides integrated information about nitrogen(N)input,transformation and output,indirectly reflecting N cycling traits within terrestrial ecosystems.However,relationships between natural 15N abundance and N cycling processes are poorly understood in China.Here,our primary objectives were to(i)examine the effects of grazing at varying levels of intensity on d15N of soils and plants in a semi-arid grassland;(ii)detect the relationships between d15N of soils and four major N cycling processes(i.e.mineralization,nitrification,denitrification and ammonia volatilization);and(iii)determine whether d15N of soils can be used as an indicator of N cycling in this semi-arid grassland.Methods The field experiment was conducted within the long-term(17-year)grazing enclosures in a semi-arid grassland in Inner Mongolia.Five grazing intensities(0.00,1.33,2.67,4.00 and 5.33 sheep ha1)were designed.d15N values of topsoils(0–10 cm),surface soils(0–2 cm)and plants were measured in 2006.Differences in d15N of soils and plants between the five grazing intensities were examined.Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons.The d15N values of topsoils were linked to the four N cycling processes to investigate their relationships.Important Findings The d15N values of topsoils(5.20–5.96&)were substantially higher than the d15N values of plants(2.51–2.93&)and surface soils(1.44–2.92&)regardless of grazing intensities.The 15N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher d15N values in topsoils than in surface soils.In addition,the d15N values of topsoils were positively correlated with the d15N values of both plants and surface soils.Grazing,especially the high-intensity grazing(5.33 sheep ha1),resulted in a significant decrease in d15N of surface soils.However,no statistically significant variations in d15N of topsoil展开更多
风干处理常对土壤中的硝化细菌数量和活性造成显著影响.为研究土壤硝化作用的干土效应,以分别发育于第四纪红土(quaternary red earth,Q)和红砂岩(tertiary red sandstone,S),利用方式为水稻(rice,R)与旱地(upland,U)的4个农田土壤的新...风干处理常对土壤中的硝化细菌数量和活性造成显著影响.为研究土壤硝化作用的干土效应,以分别发育于第四纪红土(quaternary red earth,Q)和红砂岩(tertiary red sandstone,S),利用方式为水稻(rice,R)与旱地(upland,U)的4个农田土壤的新鲜土与风干土为供试材料,进行35d的室内培养试验.结果表明,对于无外源铵输入的处理而言,旱地土壤QU的新鲜土和风干土的硝化率分别为48%和54%,SU则分别为76%和78%,硝化作用的干土效应均不显著(p>0.05);但干土效应却显著影响了水稻土的硝化作用(QR的新鲜土和风干土的硝化率分别为40%和89%,SR分别为76%和94%,p<0.01),且其风干土样的硝化作用表现出明显的微生物激活过程.外源铵的加入促进了土壤的硝化作用强度且使得旱地土壤的干土效应显著,所有供试土壤新鲜土的硝化率均显著高于风干土的硝化率.总之,土壤利用方式显著影响了硝化作用对干土效应的响应,而且利用方式和加铵对硝化作用的干土效应有着极显著的交互作用.展开更多
Partial nitrification is a key aspect of efficient nitrogen removal,although practically it suf-fers from long start-up cycles and unstable long-term operational performance.To address these drawbacks,this study inves...Partial nitrification is a key aspect of efficient nitrogen removal,although practically it suf-fers from long start-up cycles and unstable long-term operational performance.To address these drawbacks,this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine(NH2OH)on the performance of partial nitrification.Results showthat compared with the control group,low-intensity ultrasound treatment(0.10W/mL,15 min)combined with NH2OH(5 mg/L)reduced the time required for partial nitrification initiation by 6 days,increasing the nitrite accumulation rate(NAR)and ammonia nitro-gen removal rate(NRR)by 20.4% and 6.7%,respectively,achieving 96.48% NRR.Mechanis-tic analysis showed that NH2OH enhanced ammonia oxidation,inhibited nitrite-oxidizing bacteria(NOB)activity and shortened the time required for partial nitrification initiation.Furthermore,ultrasonication combined with NH2OH dosing stimulated EPS(extracellular polymeric substances)secretion,increased carbonyl,hydroxyl and amine functional group abundances and enhanced mass transfer.In addition,16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound+NH_(2)OH system,while Nitrosomonas gradually became the dominant group.Collectively,the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.展开更多
Dairy pastures can be a major source of soil nitrous oxide(N_(2)O)emissions due to the combination of intensive nitrogen(N)fertiliser use and high soil water content,from either rainfall and/or irrigation.Biochar appl...Dairy pastures can be a major source of soil nitrous oxide(N_(2)O)emissions due to the combination of intensive nitrogen(N)fertiliser use and high soil water content,from either rainfall and/or irrigation.Biochar application is a promising approach to lower soil greenhouse gas emissions,particularly under high soil moisture conditions where denitrification is the primary N-transformation pathway.In a replicated field trial,we evaluated the effects of two contrasting biochars derived from poul-try litter and from hardwood on soil N_(2)O emissions,soil ammonium(NH4^(+))and nitrate(NO3^(−))status,pasture productivity and herbage nutrient content.A liming treatment to mimic the liming equivalence of the poultry litter biochar was used to separate any effects observed from changes in soil pH.To further separate the effects of biochars on soil N status,N_(2)O emissions and pasture N uptake,high and low N fertiliser doses(annual application of 672 kg N ha^(−1),336 kg N ha^(−1))were superimposed across all of the treatments.The N fertiliser dose had no significant impact on pasture yield.Application of poultry litter biochar resulted in significant increases in pasture productivity under both high and low N inputs.This was achieved by alleviating soil P,and possibly K nutritional constraints that are typical in Australian Ferralsols.Under the high N fertiliser dose,emissions of N_(2)O from the treatments and control were not significantly different(p>0.05)and ranged between 1.14 and 1.78 kg N_(2)O-N ha^(−1)across the 11-month study.The low N dose resulted in significantly lower emissions of N_(2)O of between 0.80 and 0.84 kg N_(2)O-N ha^(−1),but biochar had no significant effect on net emissions across the season.The lack of impact of biochar on N_(2)O emissions was attributed to the relatively dry conditions over the trial period resulting in nitrification being the most likely N-transformation pathway.During brief episodes of high soil moisture,peak emissions from the biochar plots were lower than from the co展开更多
基金State Key Basic Research and Development Program of China(2010CB833502)Chinese Academy of Sciences(KZCX2-XB2-01).
文摘Aims Natural 15N abundance provides integrated information about nitrogen(N)input,transformation and output,indirectly reflecting N cycling traits within terrestrial ecosystems.However,relationships between natural 15N abundance and N cycling processes are poorly understood in China.Here,our primary objectives were to(i)examine the effects of grazing at varying levels of intensity on d15N of soils and plants in a semi-arid grassland;(ii)detect the relationships between d15N of soils and four major N cycling processes(i.e.mineralization,nitrification,denitrification and ammonia volatilization);and(iii)determine whether d15N of soils can be used as an indicator of N cycling in this semi-arid grassland.Methods The field experiment was conducted within the long-term(17-year)grazing enclosures in a semi-arid grassland in Inner Mongolia.Five grazing intensities(0.00,1.33,2.67,4.00 and 5.33 sheep ha1)were designed.d15N values of topsoils(0–10 cm),surface soils(0–2 cm)and plants were measured in 2006.Differences in d15N of soils and plants between the five grazing intensities were examined.Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons.The d15N values of topsoils were linked to the four N cycling processes to investigate their relationships.Important Findings The d15N values of topsoils(5.20–5.96&)were substantially higher than the d15N values of plants(2.51–2.93&)and surface soils(1.44–2.92&)regardless of grazing intensities.The 15N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher d15N values in topsoils than in surface soils.In addition,the d15N values of topsoils were positively correlated with the d15N values of both plants and surface soils.Grazing,especially the high-intensity grazing(5.33 sheep ha1),resulted in a significant decrease in d15N of surface soils.However,no statistically significant variations in d15N of topsoil
文摘风干处理常对土壤中的硝化细菌数量和活性造成显著影响.为研究土壤硝化作用的干土效应,以分别发育于第四纪红土(quaternary red earth,Q)和红砂岩(tertiary red sandstone,S),利用方式为水稻(rice,R)与旱地(upland,U)的4个农田土壤的新鲜土与风干土为供试材料,进行35d的室内培养试验.结果表明,对于无外源铵输入的处理而言,旱地土壤QU的新鲜土和风干土的硝化率分别为48%和54%,SU则分别为76%和78%,硝化作用的干土效应均不显著(p>0.05);但干土效应却显著影响了水稻土的硝化作用(QR的新鲜土和风干土的硝化率分别为40%和89%,SR分别为76%和94%,p<0.01),且其风干土样的硝化作用表现出明显的微生物激活过程.外源铵的加入促进了土壤的硝化作用强度且使得旱地土壤的干土效应显著,所有供试土壤新鲜土的硝化率均显著高于风干土的硝化率.总之,土壤利用方式显著影响了硝化作用对干土效应的响应,而且利用方式和加铵对硝化作用的干土效应有着极显著的交互作用.
文摘Partial nitrification is a key aspect of efficient nitrogen removal,although practically it suf-fers from long start-up cycles and unstable long-term operational performance.To address these drawbacks,this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine(NH2OH)on the performance of partial nitrification.Results showthat compared with the control group,low-intensity ultrasound treatment(0.10W/mL,15 min)combined with NH2OH(5 mg/L)reduced the time required for partial nitrification initiation by 6 days,increasing the nitrite accumulation rate(NAR)and ammonia nitro-gen removal rate(NRR)by 20.4% and 6.7%,respectively,achieving 96.48% NRR.Mechanis-tic analysis showed that NH2OH enhanced ammonia oxidation,inhibited nitrite-oxidizing bacteria(NOB)activity and shortened the time required for partial nitrification initiation.Furthermore,ultrasonication combined with NH2OH dosing stimulated EPS(extracellular polymeric substances)secretion,increased carbonyl,hydroxyl and amine functional group abundances and enhanced mass transfer.In addition,16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound+NH_(2)OH system,while Nitrosomonas gradually became the dominant group.Collectively,the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.
文摘Dairy pastures can be a major source of soil nitrous oxide(N_(2)O)emissions due to the combination of intensive nitrogen(N)fertiliser use and high soil water content,from either rainfall and/or irrigation.Biochar application is a promising approach to lower soil greenhouse gas emissions,particularly under high soil moisture conditions where denitrification is the primary N-transformation pathway.In a replicated field trial,we evaluated the effects of two contrasting biochars derived from poul-try litter and from hardwood on soil N_(2)O emissions,soil ammonium(NH4^(+))and nitrate(NO3^(−))status,pasture productivity and herbage nutrient content.A liming treatment to mimic the liming equivalence of the poultry litter biochar was used to separate any effects observed from changes in soil pH.To further separate the effects of biochars on soil N status,N_(2)O emissions and pasture N uptake,high and low N fertiliser doses(annual application of 672 kg N ha^(−1),336 kg N ha^(−1))were superimposed across all of the treatments.The N fertiliser dose had no significant impact on pasture yield.Application of poultry litter biochar resulted in significant increases in pasture productivity under both high and low N inputs.This was achieved by alleviating soil P,and possibly K nutritional constraints that are typical in Australian Ferralsols.Under the high N fertiliser dose,emissions of N_(2)O from the treatments and control were not significantly different(p>0.05)and ranged between 1.14 and 1.78 kg N_(2)O-N ha^(−1)across the 11-month study.The low N dose resulted in significantly lower emissions of N_(2)O of between 0.80 and 0.84 kg N_(2)O-N ha^(−1),but biochar had no significant effect on net emissions across the season.The lack of impact of biochar on N_(2)O emissions was attributed to the relatively dry conditions over the trial period resulting in nitrification being the most likely N-transformation pathway.During brief episodes of high soil moisture,peak emissions from the biochar plots were lower than from the co
