The Effects Of Land Use On Soil Ammonia-oxidizing Microorganisms And Its Driving Factors In Red Soil Region

Land use change/management,one of the most important aspects disturbing terrestrial ecosystems,has exerted overriding impacts on soil biogeochemical cycling and inhabitant microorganisms.As the largest population country in the world,in order to maintain food security.A large number of natural system soil was transformed into agricultural land,land use change on the influence of material cycle is one of one of the hot issues.Nitrification is an important soil nitrogen transformation process,not only directly affect the effectiveness of soil nitrogen,but also has the larger impact on the environment through nitrate leaching losses to water and N2O release into the atmosphere.Acidic soils are widely distributed in the subtropical areas southeastern China,at present,there are many research on soil nitrification in southeastern China,but dominant soil ammonia oxidation microorganism is still poorly understood in the acidic forest and agricultural soil in the subtropical areas.Therefore,it will be instructive to progress of the effects of land use on soil ammonia-oxidizing microorganisms and its driving factors for sustainable development of red soil region.Three study sites with different land use types were selected in Jiangxi Province.i.e.Upland(U),Paddy soil(P),Forest soil(F).Using the selective biomass inhibitors method combined with isotope dilution method and acetylene inhibition methods to estimate the influence of microbial inhibitor to heterotrophic nitrification and autotrophic nitrification in the different land use soils in subtropical region.The results showed that autotrophic nitrification was the predominant nitrification process in the two agricultural soils(upland and paddy),while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil.In the upland soils,streptomycin reduced autotrophic nitrification by 94%,whereas cycloheximide had no effect on autotrophic nitrification,indicating that autotrophic nitrification was mainly driven by bacteria.However,the opposite was true in another agricultural soil(paddy),indicating that fungi or archaea contributed to the ammonia-oxidizing.In the acid forest soil,cycloheximide,but not streptomycin,inhibited heterotrophic nitrification,demonstrating that fungi controlled the heterotrophic nitrification.The conversion of forest to agricultural soils resulted in the changes of the type of nitrification,drive the process of microbial species also have obvious differences.The DNA Stable-Isotope Probing(DNA-SIP)experiment was performed to determine the effects of land use change on ammonia oxidizers in acidic soils.The results showed that the ammonia oxidation was greatly associated with active of AOA in acidic forest soil.However,there was a niche separation between AOA and AOB,after the acidic forest soil converted into different agricultural land use soils(i.e.upland and paddy soils in this study).AOA played more important role than AOB in the acidic paddy soil,while,AOB was the dominant player in the acidic upland soil.Phylogenetic analysis further indicated that AOA members within the marine group1.1a-associated lineage dominated nitrification in the forest and paddy soils.Ammonia oxidation in the upland soil was catalyzed by Nitrosospira cluster 3-like AOB.The results indicated that land use change has a great effect on the niche differentiation of AOA and AOB in acidic soil.To further explore the mechanism of ammonia oxidation function differentiation,a long time flooding experiment was carrying out.The results found that the long-term flooded training can lead to ammonia oxidation microbial adaptation to the environment evolution,AOA is more suitable than AOB grow in the flood water environment.In the high ammonia and flooded environment,AOB still going on autotrophic nitrification,but without the addition of ammonium,AOA will dominate due to the ammonia concentration reduced.Thus,besides ammonia concentration,moisture is one of the environmental factors driven archaeal and bacterial ammonia oxidisers niche specialisation and differentiation.In conclusion,autotrophic nitrification was the predominant nitrification process in the two agricultural soils(upland and paddy),while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil."Active"ammonia-oxidizing microorganism is AOA Group 1.1a-associated in paddy soil.In upland soil,the main group is Cluster 3.Soil moisture is likely the control factor affecting this differentiation in the different land management soils.In the further study,it is needed to investigate the role of moisture and oxygen in the niche differentiation of AOA and AOB in acidic soil.