水稻土氧化还原状态的变化与N_2O的释放有密切关系。为揭示水稻土中Fe对N_2O释放及反硝化功能微生物的影响,本研究选取第四纪红壤发育的水稻土,设置3个水铁矿添加水平(Fe 0, 10,40 mumol g~(-1)土)和两个土壤质量含水量(50%,80%)进行土壤培养试验,利用实时荧光定量PCR (real time flourescent quantification polymerase chain reaction,qPCR)和末端限制性片段长度多态性(terminal-restricted fragment length polymorphism,T-RFLP)分析技术开展研究。结果表明,N_2O排放速率升至高峰期的过程中,外源铁处理尤其是添加高量铁(40 mumol g~(-1))处理导致硝态氮含量显著高于对照,而N_2O排放速率却明显低于对照;然而,高峰期后添加高量铁处理却维持了较对照显著高的N_2O排放速率;与此同时,添加水铁矿对硝酸还原酶基因(narG)和氧化亚氮还原酶基因(nosZ)丰度的影响表现出与N_2O排放相同的趋势,即N_2O排放速率升至高峰期的过程中,外源铁处理明显抑制了反硝化微生物的生长与繁殖,而高峰期后外源铁对反硝化微生物的抑制作用不明显。因此,水稻土中添加Fe(Ⅲ)对N_2O释放影响的主要原因可能是前期抑制了反硝化功能微生物的种群数量,从而减少了硝酸根的还原和N_2O的产生,而后期由于反硝化微生物数量的恢复和NO_3~-等含氮化合物的残留,使得外源铁处理的N_2O释放量明显高于对照。
英文摘要:
【Objective】Nitrous oxide(N_2O)is an important greenhouse gas,which is 298 times higher than carbon dioxide in Global Warming Potential(GWP)over a time scale of one hundred years. With the widespread application of chemical fertilizers and the practice of water management of alternation of drying and wetting,paddy soil has become an important source of nitrous oxide emissions. Researches show that the process of flooding-draining paddy fields can cause emissions of large amounts of nitrous oxide,and variation of the redox potential during the process is closely related to N_2O emission. Iron is a crucial redox element in paddy soil,but its influence on N_2O emission is not clear. The study is oriented to expose impacts of Fe on N_2O emission and denitrifying microorganisms. 【Method】An in-lab soil incubation experiment was carried out using samples of the paddy soil derived from the quaternary red clay. The experiment was designed to have three levels of ferrihydrite amendment(Fe 0,10 and 40 mumol g~(-1) soil)and two levels of soil water content(50% and 80%). The soil samples were air-dried and sifted through a 1mm sieve. According to the designing of the experiment,the pretreated soil samples were fully blended with ferrihydrite,separately, put into 1-L plastic boxes,200 g soil on a dry weight basis in each box,and then spiked with KNO_3 solution to ensure the samples 1.6 mumol g~(-1) soil in N content and 50% or 80% in soil water content,separately. The boxes of soil samples were placed into an incubator,28 ℃ in temperature and kept there for 24h. Air and the soils in the boxes were sampled once every 6 h during the incubation for analysis N_2O concentration in the air sample was determined with a Gas-chromatograph. Soil samples for physical and chemical analysis were stored at 4 ℃ and analyzed for NH_4~+-N and NO_3~--N contents with a continuous flow analyzer,while soil samples for microorganism analysis were quick-frozen in liquid nitrogen,and stored at -80℃,and then analyzed for variations of the communities and populations of soil denitrifying microorganisms with a real time flourescent quantification polymerase chain reaction(qPCR)and a terminal-restricted fragment length polymorphism(T-RFLP). 【Result】Results show that during the process of N_2O emission rate rising to a peak,denitrification was obviously disturbed. In the treatments spiked with extraneous iron,especially at high rates(40 mumol g~(-1)),nitrate concentrations were much higher than in CK,while N_2O emission rates were significantly lower than in control. However,after the peak,N_2O emission rate decreased markedly in all the treatments,but it did much more slowly in the treatments spiked with high rates of iron than in CK and consequently remained higher than that in CK. Meanwhile,during the first 12 hours of incubation,the abundance of nitrate reductase gene(narG)and nitrous oxide reductase gene(nosZ)varied significantly, demonstrating that the ferrihydrite spiked apparently inhibited the growth of narG-and nosZ-containing communities in population size,and the more ferrihydrite was added and the more obvious was the effect. However,after 12 hours,the inhibition effect was no longer so obvious. The addition of extraneous iron did not have much influence on structure of the denitrifying microorganism community. 【Conclusion】So it is concluded that the effect of Fe(Ⅲ)affecting population of the denitrifying microorganism community is the main cause of extraneous Fe(Ⅲ)inhibiting N_2O emission during the early period of the incubation, and hence nitrate reduction and N_2O production. But in the late period of the incubation,the recovery of denitrifying microorganisms in abundance and the existence of nitrate-containing residues,like NO_3~-,pushes the N_2O emission rate higher in the treatments spiked with extraneous iron than in CK.