Distribution And Function Of Ammonia Oxidation Microbial Community In Acidic Red Soil And Its Driving Factors

The subtropical region in China, accounting for 21% of land area, is important for industrial and agricultural production. Acidic soils of the region occupy a unique position in the world, with the features of weathering, acidic and high soil oxidation potential. It is important for environmental protection and agricultural production to study microbial nitrification of acid soil and the nitrification mechanism.The current study was carried out by the support of a long-term experimental farmland cropped with corn, the red acid soil experimental station in Jiangxi province. Four soils were collected in this study, including non-fertilized soil as control (CK), applied with nitrogen fertilizer (N), with nitrogen, phosphous and potassium (NPK) and with organic fertilizer (OM). The effect of fertilization treatments on the abundance and composition of AOA and AOB was studied by using qPCR, PCR-DGGE, cloning and sequencing. In addition, the environmental variables that drive the AOA and AOB community were analyzed. We also used DNA-SIP technology to investigate the effect of long-term fertilization on the composition and the relative abundance of functionally active AOA and AOB. The results are listed below:(1) long-term fertilization with inorganic and organic fertilizers significantly changed the abundance of AOA and AOB, and also the AOA to AOB ratio in soil. The amoA gene abundance of AOA in soil with organic fertilizers was significantly higher than the other three soils. The N-treatment and NPK treatment was significantly higher than CK treatment. The abundance of amoA gene of AOB was the highest in OM treatment and significantly higher than the other three soil treatments. There was no difference between CK, N and NPK treatments in the abundance of AOB.(2) according to the DGGE pattern of amoA gene, fertilization changed the AOB composition. Compared with CK, OM treatment changed more profoundly than N and NPK treatment in the AOA community structure. The main AOA belong to the CK, N and NPK treatments were affiliated to Group 1.1b (61.82%,50.91% and 58.18%, respectively), the rest part were affiliated to Group 1.1a associated. The AOB in OM treatment were grouped as Cluster 3 and Cluster 9, the relative abundance was 93.33% and 6.67%, respectively.(3) according to DNA-SIP technology, the contribution of AOA and AOB to autotrophic nitrification varied between fertilization treatments. The application of organic fertilizers significantly changed the active nitrifier community. The active nitrifiers were AOA in CK、N、NPK treatments. In the three treatments, the functionally active AOA belong to Group 1.1a associated, accounting for 92.73%.100%、98.18% of AOA abundance. However, in OM treatment, the functionally active nitrifiers were AOB, of them Cluster 3 and 9 account for 45% and 55% in abundance. The correlation analysis showed that soil pH, total nitrogen, ammonia-N are major environmental variables leading to the shifts of AOA and AOB abundance and the AOA community.In this study, the 15N isotopic enrichment technology together with DNA-SIP technology were applied to determine wether AOA or AOB dominated the the autotrophic nitrification rates in forestry soil. Four soil samples were collected from broad-leaf forest and coniferous forest. The results are listed below:(1) the autotrophic nitrification rates differed between vegetation types. Soil labled as B1 from broad-leaf forest exhibited the hghiest autotrophic nitrification rates 1.08 μg N g-1 soil d-1, while B4 was the lowest, nearly 0. Soil labled as C2 from coniferous forest showed a highest rate of 0.37 μg N g-1 soil d-1 while C5 the lowest value of 0.021 μg N g-1 soil d-1(2) the autotrophic nitrification rates differed with nitrifiers community. The AOB abundance in B1、B4、C2 and C5 treatments was much less than AOA. The AOA abundance was positively correlated with autotrophic nitrification rates, therefore it can be infered that AOA dominated the autotrophic nitrification process. The AOA community structure differed between treatments. The number of DGGE band and the nitrification rate showed the same trend that B1 and C2 soil were higher than B4 and B5 soil. The common bands that shared between treatments mainly belong to Group 1.1a-associated and the distinct bands belongs to Group 1.1b.(3) according to the DNA-SIP results, after 56 days incubation with DNA-SIP, the AOA and AOB abundance differed bwtween the four soil treatments. In broad-leaf forest soil B4, the copy number of AOA’s amoA gene significantly increased while the copy number in B1 soil did not change. The copy number of AOA’s amoA gene decrease in coniferous soil. Even it was undetected after urea addition. AOA of the four soil treatments degraded 13C substrates. The active AOA contained Group 1.1a-associated. In B1 and C2 treatments, only 1.9% and 3.4% active AOA belong to Group 1.1b.(4) combined with the results of last charter, the the AOA and AOB abundance in acidic subtropical soil was mainly drived by pH and ammonia content.In brief, in acidic red soils (CK, N, NPK, B1, B4, C2 and C5, pH< 5.5), the ammounia content was low (< 100 nM). The functionally active nitrifiers were AOA and mainly belonged to Group 1.la-associated. In near neutral soil (OM treatment, pH 6.4), the ammonia content was higher (365.77 nM) and AOB belonged to Cluster 3 was dominant. Therefore we suggest that the nitrifier community distribution and function were affected by land use type and the soil management. Soil pH and ammonia content are main factors drive the distribution and function.