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Ammonia-oxidising archaea (AOA) are environmentally important microorganisms involved in the biogeochemical cycling of nitrogen. Routine cultivation of AOA is exclusively performed in liquid cultures and reports on their growth on solid medium are scarce. The ability to grow AOA on solid medium would be beneficial for not only the purification of enrichment cultures but also for developing genetic tools. The aim of this study was to develop a reliable method for growing individual colonies from AOA cultures on solid medium. Three phylogenetically distinct AOA strains were tested: ' Candidatus Nitrosocosmicus franklandus C13', Nitrososphaera viennensis EN76 and ' Candidatus Nitrosotalea sinensis Nd2'. Of the gelling agents tested, agar and Bacto-agar severely inhibited growth of all three strains. In contrast, both 'Ca. N. franklandus C13' and N. viennensis EN76 tolerated Phytagel™ while the acidophilic 'Ca. N. sinensis Nd2' was completely inhibited. Based on these observations, we developed a Liquid-Solid (LS) method that involves immobilising cells in Phytagel™ and overlaying with liquid medium. This approach resulted in the development of visible distinct colonies from 'Ca. N. franklandus C13' and N. viennensis EN76 cultures and lays the groundwork for the genetic manipulation of this group of microorganisms. [ABSTRACT FROM AUTHOR]

Implementation of guidelines to reduce the amount of biodegradable municipal waste (BMW) sent to landfill has created a need in the waste-management industry to investigate possible methods of accelerating biostabilisation of residual BMW. The effect of commercially feasible manipulations (lime and green waste (GW)) on the rate of biostabilisation of the fine (<20 mm) fraction of residual BMW was investigated. The physical and chemical attributes of the composted wastes were measured, and their bacterial communities profiled using traditional culture-based methods. In addition, ammonia-oxidising microbes were monitored during the biostabilisation process using molecular profiling methods. Addition of GW accelerated biostabilisation, reduced conductivity and increased the levels of ammonia-oxidising bacterial (AOB) and archaeal (AOA) genes. The best stability was noted in the dual (Lime + GW) treatment, which was under the limit of 13 mmol O2 kg DM−1 h−1 recommended by the Irish compost standard. Biostabilised wastes met recommendations for source-segregated compost for pH (6-8) and pathogens (E. coli and Salmonella), but not heavy metals, indicating their unsuitability for uses other than landfill cover. Levels of AOA genes (log 3–6 g−1 DM) were higher than AOB (log 1–6 g−1 DM, indicating AOA may contribute more to potential ammonia oxidation in residual BMW composting. [ABSTRACT FROM AUTHOR]

The potential nitrification activity (PNA), population size and composition of AOB and AOA communities in both rhizosphere and bulk soil from a long-term (32 year) fertiliser field experiment conducted during early rice and late rice seasons were investigated by using the shaken slurry method and quantitative real-time polymerase chain reaction. The experiment begins in 1986, and including five treatments: without fertiliser input, chemical fertiliser alone, rice straw residue and chemical fertiliser, low organic manure rate and chemical fertiliser and high organic manure rate and chemical fertiliser. The results showed that the application of chemical fertiliser greatly enhanced PNA and AOB abundance, while application of rice straw residue and organic manure increased AOA abundance. Moreover, the results showed that the PNA and population sizes of AOB and AOA were higher in the rhizosphere than in the bulk soil. Cluster and redundancy analyses further indicated that the rhizosphere effect play a more important role in shaping AOA community structure than long-term fertilization. In summary, the results indicated that AOB rather than AOA functionally dominate ammonia oxidation in the double-cropping rice paddy soils, and that rhizosphere effect and fertiliser regime play different roles in the activity and community structures of AOB and AOA.

Ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) are ammonium oxidising prokaryotes that can drive soil nitrification in wetlands. During the restoration of wetlands, different types of land use soils (agricultural soil [AS], restored wetland soil [RS], and natural wetland soil [NWS]) are present. However, studies on the effects of changes in the types of land use in wetlands during restoration on nitrification and the community composition of AOA and AOB are still not well understood. In this study, the differences in the potential nitrification rate (PNR) and community composition of AOA and AOB in AS, RS, and NWS were compared and discussed. The results indicated that the PNRs in the AS, RS, and NWS were on the same order of magnitude. Nitrification was mainly driven by AOB. High-throughput sequencing results showed that the genus Nitrososphaera of AOA and unclassified_o_Nitrosomonadales of AOB were only detected in the AS. Redundancy analysis (RDA) results indicated that the community composition of AOA was mostly influenced by pH, while TC was the most influential variable on the community composition of AOB. Our study provides a basis for distinguishing the roles of ammonium-oxidising prokaryotes in nitrification and further understanding the changes in nitrifying activity in wetlands during restoration. [ABSTRACT FROM AUTHOR]

The potential nitrification activity (PNA), population size and composition of AOB and AOA communities in both rhizosphere and bulk soil from a long-term (32 year) fertiliser field experiment conducted during early rice and late rice seasons were investigated by using the shaken slurry method and quantitative real-time polymerase chain reaction. The experiment begins in 1986, and including five treatments: without fertiliser input, chemical fertiliser alone, rice straw residue and chemical fertiliser, low organic manure rate and chemical fertiliser and high organic manure rate and chemical fertiliser. The results showed that the application of chemical fertiliser greatly enhanced PNA and AOB abundance, while application of rice straw residue and organic manure increased AOA abundance. Moreover, the results showed that the PNA and population sizes of AOB and AOA were higher in the rhizosphere than in the bulk soil. Cluster and redundancy analyses further indicated that the rhizosphere effect play a more important role in shaping AOA community structure than long-term fertilization. In summary, the results indicated that AOB rather than AOA functionally dominate ammonia oxidation in the double-cropping rice paddy soils, and that rhizosphere effect and fertiliser regime play different roles in the activity and community structures of AOB and AOA. [ABSTRACT FROM AUTHOR]

Purpose: In New Zealand, the application of farm dairy effluent (FDE) on pasture soils is the third largest source of nitrous oxide (N2O) emissions from grazed grassland. Recently, new FDE treatment technologies have been developed to produce clarified water (CW) and treated effluent (TE) to recycle water and reduce the volume of fresh water used at the farm dairy. The aim of this study was to compare the effects of CW and TE with those of FDE on N2O emissions and the growth of ammonia-oxidising bacteria (AOB), ammonia-oxidising archaea (AOA) and denitrifiers, when the effluents were applied to a grazed pasture soil. Materials and methods: A microcosm incubation study was carried out to determine the effects of applying CW, TE and untreated FDE, with or without animal urine, on N2O emissions, and the abundance of AOB, AOA and the denitrifying functional genes, including nirS, nirK and nosZ. The soil used was a Templeton silt loam (Udic Haplustepsts). The effluents were applied at nitrogen (N) rates equivalent to 100 kg N ha−1 and the animal urine at 700 kg N ha−1. The soils were incubated at 12 °C to simulate autumn/winter soil temperatures in New Zealand, and the soil moisture was maintained at field capacity. Results and discussion: Results showed that the application of all the different effluents significantly increased the total N2O emissions (0.21–0.28 kg N2O-N ha−1) compared with that in the control (0.18 kg N2O-N ha−1). However, there were no significant differences in total N2O emissions between the different effluent treatments. Similarly, although the application of animal urine together with the different effluents further increased N2O emissions (7.7–8.8 kg N2O-N ha−1) above that from the urine only treatment (5.8 kg N2O-N ha−1), there were no significant differences among the different effluent plus urine treatments. These N2O results corresponded with the changing trends of the abundance of AOB, AOA, nirS, nirK and nosZ, that is the application of the CW, TE and FDE, with or without animal urine, had a similar impact on the growth dynamics of these microbial populations. Conclusions: These results indicate that the application of the CW and TE to dairy pasture soils would have a similar effect on N2O emissions, ammonia oxidisers and denitrifiers as that of the untreated FDE, with or without animal urine. The treated effluent or clear water from the new effluent treatment technology would therefore not increase N2O emissions nor adversely affect the key microbial populations involved in N cycling in soil. [ABSTRACT FROM AUTHOR]

Abstract Quorum sensing (QS) regulation of the composition of ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) communities and functions in wastewater treatment was investigated. Specifically, we explored the role of N -acyl- l -homoserine lactones (AHLs) in microbial community dynamics in activated sludge. On average, the specific ammonia-oxidising-rate increased from 1.6 to 2.8 mg NH 4 +-N/g MLSS/hr after treatment with long-chain AHLs for 16 days, and the addition of AHLs to sludge resulted in an increased number of AOA/AOB amoA genes. Significant differences were observed in the AOA communities of control and AHL-treated cultures, but not the AOB community. Furthermore, the dominant functional AOA strains of the Crenarchaeota altered their ecological niche in response to AHL addition. These results provide evidence that AHLs play an important role in mediating AOA/AOB microbial community parameters and demonstrate the potential for application of QS to the regulation of nitrogen compound metabolism in wastewater treatment. Graphical abstract AHLs have an important role in mediating AOA/AOB microbial community parameters, and this discovery shows possibility of applying QS to the regulation of nitrogen compound metabolism in wastewater treatment. Unlabelled Image [ABSTRACT FROM AUTHOR]

Climate change causes droughts, which in turn cause significant physiological stress for soil microorganisms. In this study, we investigated how the abundance of total bacterial, crenarchaeal and fungal communities and the abundance of N-cycling microbial guilds responded to a severe agricultural drought event in a long-term experiment of minimum tillage (MT) and conventional ploughing (CT) at two soil depths. Drought, defined as a reduction of soil water content and increased soil temperature, significantly decreased the abundance of all the studied microbial communities. The data showed linear relationships between all dependent variables and soil water content and soil temperature for the examined range of soil water content (WHC 13–76%) and examined range of average daily soil temperature at 5 cm depth (17–30 °C). Thus, we found that the abundance of most studied microbial communities decreased by about 2% when water content decreased by 1 mass % and by about 10% when temperature increases by 1 °C. When comparing communities at average soil water content and average soil temperature, MT had higher average abundances of total bacterial and crenarchaeal 16S rRNA and fungal ITS genes in the 0–10 cm soil layer than did CT (1.9, 2.9 and 2.5 times, respectively), as well as AOA and AOB amoA (3.9 and 1.7 times, respectively), nirK , nirS , nosZ I and nosZ II genes (2.0, 1.8, 1.8 and 2.3 times, respectively); while significant differences between MT and CT in the 10–20 cm soil layer were found only in the average abundance of crenarchaeal 16S rRNA and crenarchaeal amoA genes (3.5 and 2.7 times greater under MT than CT). Regardless of the weather conditions during our study, the abundances of all communities were greater under MT 0–10 than under CT 0–10. After three weeks of severe drought, the greatest decrease in the abundance of all communities, bacterial and archaeal N-cycling guilds as well as total prokaryotes and fungi, was observed under MT 0–10. However, after only a few rainfall events, all communities under both tillage systems reached their initial abundance, demonstrating a high resilience. [ABSTRACT FROM AUTHOR]

Coastal areas worldwide are challenged by climate change-associated increases in sea level and storm surge quantities that potentially lead to more frequent flooding of soil ecosystems. Currently, little is known of the effects of inundation events on microorganisms controlling nitrification in these ecosystems. The goal of this study was to investigate the impact of seawater flooding on the abundance, community composition and salinity tolerance of soil ammonia oxidisers. Topsoil was sampled from three islands flooded at different frequencies by the Wadden Sea. Archaeal ammonia oxidiser amoA genes were more abundant than their betaproteobacterial counterparts, and the distribution of archaeal and bacterial ammonia oxidiser amoA and 16S rRNA gene sequences significantly differed between the islands. The findings indicate selection of ammonia oxidiser phylotypes with greater tolerance to high salinity and slightly alkaline pH (e.g. Nitrosopumilus representatives) in frequently flooded soils. A cluster phylogenetically related to gammaproteobacterial ammonia oxidisers was detected in all samples analysed in this survey. Nevertheless, no gammaprotebacterial amoA genes could be amplified via PCR and only betaproteobacterial ammonia oxidisers were detected in enrichment cultures. A slurry-based experiment demonstrated the tolerance of both bacterial and archaeal ammonia oxidisers to a wide range of salinities (e.g. Wadden Sea water salinity) in soil naturally exposed to seawater at a high frequency. [ABSTRACT FROM AUTHOR]

Ammonia oxidising archaea (AOA) are an abundant and ubiquitously distributed group of soil microorganisms and contribute significantly to nitrogen cycling processes. Soil pH has been identified as a major driver of AOA diversification, but other environmental factors may also be important. The aim of this study was to determine whether soil pH also influenced the temperature range of AOA activity in soil. This was assessed by determining rates of ammonification and net nitrification, and AOA abundance and community composition during incubation of soils with pH in the range 3.6–7.5 at 20, 30 or 40 °C for 30 days. Net nitrification was greatest at 20 or 30 °C, with variation in optimal temperature between soils, net nitrification was not detectable at 40 °C, and mineralisation was greatest at 40 °C. AOA community composition differed following incubation at 20° and 30 °C, presumably through selection and growth of populations with different temperature optima, and, at 40 °C, due to cell death. There was no significant relationship between thaumarchaeotal cell abundance and yield estimated using amoA and 16S rRNA genes, possibly due to amplification of 16S rRNA genes of non-ammonia-oxidising Thaumarchaeota. However, amoA gene abundance and yield were greater at 20 °C than 30 °C in the most acidic soils, with the opposite relationship for the most neutral soils. This is consistent with cultivated lower temperature optima for neutrophilic, rather than acidophilic soil AOA. The results indicate that pH-driven diversification may have consequences for other aspects of AOA physiology including temperature optima for growth and activity in the environment. [ABSTRACT FROM AUTHOR]

The influence of plants on archaeal (AOA) and bacterial (AOB) ammonia oxidisers (AO) is poorly understood. Higher microbial activity in the rhizosphere, including organic nitrogen (N) mineralisation, may stimulate both groups, while ammonia uptake by plants may favour AOA, considered to prefer lower ammonia concentration. We therefore hypothesised (i) higher AOA and AOB abundances in the rhizosphere than bulk soil and (ii) that AOA are favoured over AOB in the rhizosphere of plants with an exploitative strategy and high N demand, especially (iii) during early growth, when plant N uptake is higher. These hypotheses were tested by growing 20 grassland plants, covering a spectrum of resource-use strategies, and determining AOA and AOB amoA gene abundances, rhizosphere and bulk soil characteristics and plant functional traits. Joint Bayesian mixed models indicated no increase in AO in the rhizosphere, but revealed that AOA were more abundant in the rhizosphere of exploitative plants, mostly grasses, and less abundant under conservative plants. In contrast, AOB abundance in the rhizosphere and bulk soil depended on pH, rather than plant traits. These findings provide a mechanistic basis for plant-ammonia oxidiser interactions and for links between plant functional traits and ammonia oxidiser ecology. [ABSTRACT FROM AUTHOR]

Clone library construction and quantitative polymerase chain reaction were used to investigate the effects of three emergent aquatic plant species ( Iris pseudacorus , Thalia dealbata and Typha orientalis L.) on the abundances and community structures of ammonia-oxidising archaea (AOA) and bacteria (AOB). The abundances of archaeal and bacterial amoA genes ranged from 2.91 × 10 7 to 3.20 × 10 9 and 1.03 × 10 7 to 5.10 × 10 8 , respectively. At the study area, T. orientalis showed the highest abundances of AOA and AOB. I. pseudacorus harbored higher AOA richness and diversity than T. orientalis , but lowest AOB abundance. Nitrososphaera, Nitrosopumilus and Nitrosotalea clusters were observed in AOA, in which the Nitrososphaera cluster was predominant. Moreover, Nitrosomonas and Nitrosospira clusters were detected in AOB, in which the Nitrosospira cluster was dominant. Assays of potential nitrification rates (PNRs) in the samples cultivated with or without ampicillin suggested that AOA may be important in nitrification in unvegetated and I. pseudacorus -associated sediments, whereas AOB may dominate nitrification in the other species. [ABSTRACT FROM AUTHOR]

Purpose: Dairy winter forage grazing on free-draining soils is a common practice within the Canterbury region of New Zealand. The high stocking rates involved and the associated deposition of urine onto wet soils during winter create a high risk of nitrate (NO) leaching from soil. The objective of this study was to determine the effect of animal trampling and the use of a nitrification inhibitor, dicyandiamide (DCD), on soil ammonia oxidisers, nitrification, and nitrate leaching under simulated winter forage grazing conditions. Materials and methods: A lysimeter trial was carried out using a Balmoral stony silt loam under a kale forage crop. Nitrate leaching losses, the effect of soil trampling, and the effect of DCD were measured. Soil nitrification rates and ammonia-oxidising community abundance and activity were measured in companion soil blocks under simulated dairy winter forage grazing conditions. Results and discussion: Animal trampling was found to reduce peak nitrate-N (NO-N) concentrations in drainage water from urine patch areas by 43 %. In addition, animal trampling reduced the total amount of NO-N leached from urine patches by 34 %. However, animal trampling did not affect the growth or activity of the ammonia oxidisers. The use of DCD was found to be highly effective in reducing the concentration and amount of NO-N leached from urine patches. Dicyandiamide applications reduced peak NO-N concentrations in drainage water by 66 %, and the total amount of NO-N leached was reduced by 61 % under the simulated dairy winter forage grazing conditions. Ammonia oxidising bacteria (AOB) were more abundant than ammonia-oxidising archaea (AOA) and were responsible for mediating the nitrification process. Conclusions: These results suggest that both animal trampling and the use of DCD separately reduces soil nitrification rates and thus NO leaching. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase the frequency of severe drought events followed by heavy rainfall, which will influence growth and activity of soil microorganisms, through osmotic stress and changes in nutrient concentration. There is evidence of rapid recovery of processes and adaptation of communities in soils regularly experiencing drying/rewetting and lower resistance and resilience in nonadapted soils. A microcosm-based study of ammonia-oxidising archaea (AOA) and bacteria (AOB), employing a grassland soil that rarely experiences drought, was used to test this hypothesis and also whether AOB were more resistant and resilient, through greater tolerance of high ammonia concentrations produced during drought and rewetting. Treated soils were dried, incubated for 3 weeks, rewetted, incubated for a further 3 weeks and compared to untreated soils, maintained at a constant moisture content. Nitrate accumulation and AOA and AOB abundance (abundance of respective amoA genes) and community composition (DGGE analysis of AOA amoA and AOB 16S rRNA genes) were poorly adapted to drying-rewetting. AOA abundance and community composition were less resistant than AOB during drought and less resilient after rewetting, at times when ammonium concentration was higher. Data provide evidence for poor adaptation of microbial communities and processes to drying-rewetting in soils with no history of drought and indicate niche differentiation of AOA and AOB associated with high ammonia concentration. [ABSTRACT FROM AUTHOR]

Ammonia-oxidising archaea (AOA) are increasingly recognised as the primary mediators of soil ammonia oxidation, particularly in acidic soils. To explore the niche segregation of AOA and ammonia-oxidising bacteria (AOB) and the potential effect of this segregation on nitrification rates and the nitrogen cycle in Chinese agricultural soils, AOA and AOB amoA gene databases were established, and 454 high-throughput sequencing was used to investigate the key factors leading to the niche segregation of these two types of microorganisms. qPCR results demonstrated that there were more functional genes for AOA than for AOB in most of the soils. AOA diversity was higher than AOB diversity in most of the soils with AOA operational taxonomic units (OTU) numbers ranging from 40 to 169 and AOB OTU numbers ranging from 18 to 105. pH was the most important factor influencing the community structure of AOA ( P < 0.01) and AOB ( P < 0.05), and acidophilic AOA (i.e. Nitrosotalea-related sequences) were dominant in soils with pH values below 6.0. In addition, AOA amoA gene copy numbers were significantly positively correlated with pH ( P < 0.05), the ratio of AOA OTU numbers/AOB OTU numbers was significantly negatively correlated with pH ( P < 0.05), and the percentage of sequences represented by the Nitrosotalea cluster was significantly negatively correlated with pH ( P < 0.01). [ABSTRACT FROM AUTHOR]

Autotrophic ammonia oxidation is performed by two distinct groups of microorganisms: ammonia-oxidising archaea ( AOA) and ammonia-oxidising bacteria ( AOB). AOA outnumber their bacterial counterparts in many soils, at times by several orders of magnitude, but relatively little is known of their physiology due to the lack of cultivated isolates. Although a number of AOA have been cultivated from soil, Nitrososphaera viennensis was the sole terrestrial AOA in pure culture and requires pyruvate for growth in the laboratory. Here, we describe isolation in pure culture and characterisation of two acidophilic terrestrial AOA representing the Candidatus genus Nitrosotalea and their responses to organic acids. Interestingly, despite their close phylogenetic relatedness, the two Nitrosotalea strains exhibited differences in physiological features, including specific growth rate, temperature preference and to an extent, response to organic compounds. In contrast to N. viennensis, both Nitrosotalea isolates were inhibited by pyruvate but their growth yield increased in the presence of oxaloacetate. This study demonstrates physiological diversity within AOA species and between different AOA genera. Different preferences for organic compounds potentially influence the favoured localisation of ammonia oxidisers within the soil and the structure of ammonia-oxidising communities in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Autotrophic archaeal and bacterial ammonia-oxidisers (AOA and AOB) drive soil nitrification. Ammonia limitation, mixotrophy, and pH have been suggested as factors providing niche specialisation and differentiation between soil AOA and AOB. However, current data from genomes, cultures, field studies, and microcosms suggest that no single factor discriminates between AOA and AOB. In addition, there appears to be sufficient physiological diversity within each group for growth and activity in all soils investigated, with the exception of acidic soils (pH <5.5), which are dominated by AOA. Future investigation of niche specialisation in ammonia-oxidisers, and other microbial communities, requires characterisation of a wider range of environmentally representative cultures, emphasis on experimental studies rather than surveys, and greater consideration of small-scale soil heterogeneity. [ABSTRACT FROM AUTHOR]

1. Community structures of planktonic ammonia-oxidising archaea (AOA) and bacteria (AOB) were investigated for five high-altitude Tibetan lakes, which could be classified as freshwater, oligosaline or mesosaline, to develop a general view of the AOA and AOB in lakes on the Tibetan Plateau. 2. Based on PCR screening of the ammonia monooxygenase α-subunit ( amoA) gene, AOA were present in 14 out of 17 samples, whereas AOB were detected in only four samples. Phylogenetic analyses indicated that the AOB communities were dominated by a unique monophylogenetic lineage within Nitrosomonas, which may represent a novel cluster of AOB. AOA, on the other hand, were distinct among lakes with different salinities. 3. Multivariate statistical analyses indicated a heterogeneous distribution of the AOA communities among lakes largely caused by lake salinity, whereas the uniform chemical properties within lakes and their geographical isolation may favour relatively homogeneous AOA communities within lakes. 4. Our results suggest a wide occurrence of AOA in Tibetan lakes and provide the first evidence of salinity-related differentiation of AOA community composition as well as potential geographical isolation of AOA in inland aquatic environments. [ABSTRACT FROM AUTHOR]

• Soil nitrification potential increased with increasing amount of chemical fertiliser. • Green manuring changes the nitrification process by affecting recovered nitrification potential. • Green manuring directly affected the contribution of ammonia-oxidising archaea to nitrification. Rice–rice–green manure rotation is a cropping system that effectively maintains high yields and improves soil fertility. Nitrification, a critical process in N cycling, is affected by different fertilisation regimes, but the roles of ammonia-oxidising bacteria (AOB) and ammonia-oxidising archaea (AOA) in nitrification and their shift in abundance and diversity in response to long-term green manure application in alkaline paddy soil is poorly understood. In the present work, nitrification potential (NP), the contributions of AOA and AOB to nitrification, abundances, and communities of AOA and AOB were studied to mechanistically understand the effects of green manuring and fertilisation regimes on nitrification and ammonia oxidisers. Results showed that the combination of green manure and reduced chemical fertiliser increased grain yields. Soil NP increased with increasing amount of chemical fertiliser. The combination of green manure and different rates of chemical fertiliser promoted the soil recovered nitrification potential (RNP) and the contribution of AOB to nitrification (RNP AOB). Differences in AOA and AOB communities revealed that an increase in the abundance of Nitrosopumilus in AOA and a decrease in the abundance of Nirosomonas in AOB were observed in green manure treatment compared with those of chemical fertiliser treatments. Partial least squares path modelling showed that chemical fertilisation exerts direct effects on NP whereas green manuring markedly influenced RNP. For the relative contributions of AOA (RNP AOA) and AOB, RNP AOB were correlated with chemical fertilisation, whereas green manuring directly affected RNP AOA. In conclusion, green manuring changed the nitrification process by affecting RNP, whereas chemical fertiliser directly influenced NP. Changes in AOA composition and their impact on nitrification might reflect a mechanism worthy of further research. [ABSTRACT FROM AUTHOR]