Font Size: a A A

Effects Of Iron Oxide And Organic Matter On Acidic Soil Nitrification

Posted on:2017-05-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:X R HuangFull Text:PDF
GTID:1313330536451749Subject:Agricultural resources and the environment
Abstract/Summary:PDF Full Text Request
Nitrification in acidic soil is spatial variability,and it is difficult to be interpreted by the availability of pH and NH3 and the community of ammonia-oxidizing microorganisms,indicating that some unknown factors may play critical role in nitrification in acidic soil.Soils,especially for the tropic and subtropics acidic soils,contain a great amount of iron oxide and organic matter.The different effects of pH,water content and iron oxidation/reduction bacteria on soil N transformation lead to different soil nitrification.As an indispensable component,organic matter in soil not only releases N through decomposition,but also immobilizes soil inorganic N,to influence N circulation.Therefore to understand the relation between Fe oxide/organic matter and nitrification is important to understand N circulation.Moreover,the ecological function between AOA and AOB are the same though their community are different.With the effect of environment,AOA and AOB may have ecological coexistence mechanism.To aim at these scientific question such as the role of soil abiotic factors?iron oxide and organic matter?in acidic soil nitrification,the origin of NH3,dominated microbes of nitrification,this study used 15N tracing technology,MPN methods,DNA-SIP,q PCR,clone and pyrosequencing,to research the influencing mechanism of coupling effects of biotic/abiotic factors and the coexistence mechanism of ammonia-oxidizing microorganisms in nitrification process.First,with normal culture,the soil nitrification was studied with the addition of iron oxide and organic matter under conditions of different soil pH and water content.Under a determinate water content,after adding iron oxide and organic matter,the soil nitrification was higher under 100% WHC than under 50% and 200% WHC.Under 100% WHC,the nitrification in strong acidic soil?pH 4.3-4.8?was negative whether iron oxide and organic matter were added or not,indicating that iron oxide and organic matter cannot influence nitrification in strong acidic soil.Under 100% WHC,with the addition of both iron oxide and organic matter,it stimulated soil nitrification in soil of pH 5.1 but restrained nitrification in soil of pH 7.8.This mainly because the redox activity of iron oxide under 100% WHC is influenced by the soil pH,thus resulting in different nitrification in low and high pH soil.With only organic matter added,soil nitrification was significantly restrained in soils of pH 5.1,6.0 and 7.8.Then,according to the normal experimental results,under 100% WHC,the addition of iron oxide or iron oxide and organic matter significantly stimulated the nitrification in low pH soil?pH 5.1?,but restrained the nitrification in high soil?pH 7.8?.With 15N tracer technique,this study explored the mechanism of different nitrification that effected by iron oxide in different pH soil.It found that,in low pH soil,iron oxide promoted the soil net nitrification and gross mineralization rate,but decreased the microbial immobilization of inorganic N;however,the opposite results were found in high pH soil.Compared to the control,Fe oxide decreased microbial immobilization of inorganic N by 50% in low pH soil but increased it by 45% in high pH soil.These findings explained the results of normal experimental.It indicated that the effect of iron oxide on nitrification is influenced by soil pH,and for different pH soil,the mechanism of iron oxide affecting nitrification is different.Secondly,with 15N tracer technique and the most probable number method?MPN?,we studied the relation between iron oxide and soil nitrification under the effects of soil Fe reduction/oxidation microbial at different depth of acidic paddy soil.The change trends of gross nitrification rate and gross mineralization rate with the increasing of soil depth were the same.The nitrification rates in soil depth of 0-10,10-20 and 20-40 cm,whose difference were not significant,were 7,7 and 5 times larger than that in soil depth of >40 cm.The abundance of Fe reducing bacteria and oxidizing bacteria in soil depth of 0-10,10-20 and 20-40 cm were 10-100 times larger than in soil depth of >40 cm,and their change trends were the same with soil nitrification.The gross immobilization rate of NH4+ in 10-20 and 20-40 cm depth decreased by 71% and 29% comparing with that in 0-10 cm depth,indicating that Fe reducing bacteria positively correlated to the total Fe and effective Fe in soil depth of 0-10,10-20 and 20-40 cm.Fe oxidizing bacteria positively correlated to organic matter and NH4+ content,and organic matter positively corrected to the total Fe and effective Fe and NH4+ content,which indicted that Fe oxides and organic matter affect the conversion of the NH4+ in soil directly,and the effect of Fe reducing/oxidizing bacteria in this process cannot be ignored.Fe oxides are likely to be reduced by the Fe oxidizing bacteria,promoting the oxidation of organic matter,thus increasing the concentration of NH3.The soil nitrification at different depth of paddy soil was influenced by both iron oxide and Fe reducing/oxidizing bacteria.Thirdly,to aim at the ecological niche differentiation of microbial in soil,with DNA-based stable isotope probing?DNA-SIP?technology,the nitrification and community structure of nitrification microbial were studied.Soil nitrification in acidic forest soil turns to be significant only with the addition of urea.In acidic forest soil,the abundance of aom A gene is higher in AOA than that in AOB,but only AOB with urea addition is labeled by 13C.It indicates that soil nitrification in forest soil is dominated by AOB,because AOB have urease activity,and the applied urea stimulates the rise in AOB and increases the concentration of NH3 substrate through hydrolysis to improve nitrification.It also found that in acidic forest soil with an addition of 5% neutral purple soil,no matter urea or?NH4?2SO4 was added,soil nitrification was strong and AOB in two treatments were labeled.The increasing amount of nitrification rate in acidic forest soil with an addition of 5% neutral purple soil and with urea added was 3 times larger than that in acidic forest soil,and the increasing amount of abundance of aom A gene in AOB in former was 27 times larger than in latter.The addition of 5% purple soil disturbed the community of AOB in acidic forest soil.The functional AOB that play a role in ammonia oxidation in acid forest soil with and without 5% purple soil addition were Nitrosomonas and Nitrosospira,respectively.AOB in acidic forest soil with different treatments selectively stimulated soil nitrification.The gene sequence of amo A of AOA in acid forest soil with and without 5% purple soil addition distributed in Group1.1b.In summary,in soil ecosystem,Fe oxide and organic matter play important roles in soil nitrification and other N transformation processes.The effect of Fe oxide on soil nitrification varies with environment condition.Fe reducing/oxidizing bacteria and Fe oxide work together to influence soil nitrification.The difference of community between AOA and AOB may be the main reason for different driver of soil nitrification,and with 5% neutral purple soil addition in acidic forest soil,the group of AOB changed and coexisted with other ammonia-oxidizing microorganism to play a role in ammonia oxidation.
Keywords/Search Tags:N transformation, Mineralization, Immobilization, Fe reducing/oxidizing bacteria, Ammonia-oxidizing bacteria/archaea
PDF Full Text Request
Related items