amoA Gene Abundance Research Articles

Newly designed primer pair revealed dominant and diverse comammox amoA gene in full-scale wastewater treatment plants

The discovery of complete ammonia oxidizing bacteria (CAOB) capable of performing the two-step nitrification process on their own has fundamentally upended our traditional perception. However, their environmental distribution and ecological significance in driving ammonia oxidation are still urgently awaited to be assessed. In this study, the diversity and abundance of CAOB amoA gene in wastewater treatment plants (WWTPs) were presented taking advantage of a newly designed primer pair specifically targeting CAOB amoA gene. Phylogenetic results demonstrated the novel amoA gene formed a clearly distinct cluster from the canonical amoA and pmoA genes. Among the five well-supported sub-clusters, Nitrospira nitrosa cluster accounted for 94.34% of all the currently retrieved sequences from WWTPs. More importantly, qPCR results demonstrated a remarkably high abundance of CAOB amoA gene, which were up to 182.7-fold more abundant than AOB amoA gene. This study provided new dimension and fundamental basis for future researches towards biogeochemical nitrogen cycle.

Does influent surface organic loading and aeration mode affect nitrogen removal and N2O emission in subsurface wastewater infiltration systems?

This study evaluated the influence of influent surface organic loading (SOL) and aeration mode on nitrogen removal and N2O emission in subsurface wastewater infiltration systems (SWISs). Aeration developed appropriate oxygen conditions, which resulted in high COD, NH4+-N and TN removal and enhanced the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB and nosZ under SOL rate of 21.2 and 33.8 g COD/(m2 d) compared to the non-aerated SWIS. N2O emission decreased with influent SOL rate increasing in non-aerated and aerated SWISs. The SWIS with intermittent aeration had a better performance on TN removal and lower N2O emission compared to the SWIS with continuous aeration under the same SOL rate. It could conclude that intermittent aeration is a feasible method to win high influent SOL rate, high TN removal and low N2O emission for SWISs.

Effects of Aquaculture on Ammonia-oxidizing Prokaryotes in Sediments of Eastern Lake Taihu

The abundance and diversity of ammonia-oxidizing microorganisms in sediments of an aquacultural area of Eastern Lake Taihu were investigated. Real-time quantitative PCR was used to analyze the abundance of archaeal and bacterial amoA genes. Cloned libraries were constructed to investigate the structure and diversity of the microbial community. By comparing community characteristics of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in different zones, we found that:①Copy numbers of the bacterial amoA gene outnumbered those of archaeal amoA genes in the aquacultural zone; ②Diversity of AOA and AOB was higher in the aquaculture zone and control zone, respectively; ③ The dominant cluster of AOA and AOB in both sediments of aquiculture zone and control zone was Nitrosopumilus and Nitrosospira respectively. It was therefore the community structure of AOA (rather than AOB) in lake sediments that was affected by aquacultural activity.

Key environmental factors to variation of ammonia-oxidizing archaea community and potential ammonia oxidation rate during agricultural waste composting

In this research, the abundance and structure of AOA amoA gene during agricultural waste composting were determined by quantitative PCR and sequencing techniques, respectively. Pairwise correlations between potential ammonia oxidation (PAO) rate, physicochemical parameters and the AOA abundance were evaluated using Pearson correlation coefficient. Relationships between these parameters, PAO rates and AOA community structure were evaluated by redundancy analysis. Results showed that 22 AOA gene OTUs were divided into the soil/sediment lineage by phylogenetic analyses. Significant positive correlations were obtained between AOA amoA gene abundance and moisture, ammonium, water soluble carbon (WSC) and organic matter (OM), respectively. Redundancy analysis showed OM, pH and nitrate significantly explained the AOA amoA gene structure. Pearson correlation revealed the PAO rate correlated positively to ammonium, AOA amoA gene abundance. These results indicated that AOA communities sense the fluctuations in surrounding environment, and ultimately react and influence the nitrogen transformation during agricultural waste composting.

Niche separation of comammox Nitrospira and canonical ammonia oxidizers in an acidic subtropical forest soil under long-term nitrogen deposition

The recent discovery of comammox Nitrospira capable of converting ammonia to nitrate in a single organism radically challenged our century-long perception of the classic two-step nitrification performed by ammonia oxidizers and nitrite oxidizers. However, our understanding of the niche separation of comammox Nitrospira and canonical nitrifiers in forest ecosystems remains limited, especially under a global scenario of elevated nitrogen (N) deposition. Here we evaluated the impacts of six-year N deposition on the dynamics of comammox Nitrospira, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in a subtropical forest soil. Soil inorganic N concentrations significantly increased under the six-year simulation of N deposition, while soil pH, available phosphorus, total carbon (C), C/N ratio and microbial biomass significantly decreased. Quantitative PCR showed that the amoA gene abundances of comammox Nitrospira clade B and AOA substantially increased under the increasing rates of N deposition. By contrast, the AOB amoA gene abundance significantly decreased with the higher levels of N deposition (100 and 150 kg N ha−1 yr−1). Increased 13CO2 incorporation into the AOA communities, rather than comammox Nitrospira or AOB, was demonstrated in a DNA-stable isotope probing microcosm, indicative of the capacity of AOA to assimilate 13CO2 through autotrophic nitrification in the investigated subtropical forest soil under long-term N deposition. Phylogenetic analysis revealed that the autotrophic AOA assemblages belonged to the Nitrosotalea cluster, and their capacity for assimilating CO2 through autotrophic nitrification was not affected by the long-term N deposition. Taken together, we provided new evidence for the niche separation of comammox Nitrospira and canonical ammonia oxidizers in soil nitrification under the long-term N deposition in the acidic subtropical forest soil.

Nitrogen Removal and N₂O Emission in Biochar-Sludge Subsurface Wastewater Infiltration Systems.

Nitrogen removal and N2O emission of biochar-sludge amended subsurface wastewater infiltration systems (SWISs) with/without intermittent aeration under different organic surface loading rates (OSLRs) were investigated. Under OSLR, between 8.5 and 54.6 g COD/(m2 d), average chemical oxygen demand (COD), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm01.gif"/>, and total nitrogen (TN) removal rates decreased with OSLR increasing in non-aerated SWISs amended with/without biochar-sludge; increasing OSLR hardly affected COD and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm12.gif"/> removal in biochar-sludge amended SWIS with intermittent aeration; N2O emission rate decreased with influent OSLR increasing in the SWISs. Biochar-sludge amended SWIS with intermittent aeration obtained higher removal rates for COD (94.9 to 95.5%), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00800-ilm23.gif"/> (90.5 to 93.7%), TN (86.5 to 89.9%) and lower N2O emission rates [13.4 to 14.7 mg/(m2 d)] under high influent OSLR of 36.2 and 54.6 g COD/(m2 d) were compared with non-aerated SWISs with/without biochar-sludge. Furthermore, the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ genes involved in nitrogen removal were enhanced under high influent OSLR in biochar-sludge amended SWIS with intermittent aeration.

The more important role of archaea than bacteria in nitrification of wastewater treatment plants in cold season despite their numerical relationships

Nitrification failure of wastewater treatment plants (WWTPs) in cold season calls into investigations of the functional ammonia-oxidizing microorganisms (AOMs). In this study, we report the abundance of ammonia-oxidizing archaea (AOA), bacteria (AOB) and complete ammonia-oxidizing (comammox) Nitrospira in 23 municipal WWTPs in cold season, and explore the correlations between AOMs abundance and their relative contribution to nitrification. The copy numbers of AOA and AOB amoA gene ranged from 2.42 × 107 to 2.47 × 109 and 5.54 × 106 to 3.31 × 109 copies/g sludge, respectively. The abundance of amoA gene of Candidatus Nitrospira inopinata, an important strain of comammox Nitrospira, was stable with averaged abundance of 8.47 × 106 copies/g sludge. DNA-based stable isotope probing (DNA-SIP) assays were conducted with three typical WWTPs in which the abundance of AOA was lower than, similar to and higher than that of AOB, respectively. The results showed that considerable 13C-assimilation by AOA was detected during active nitrification in all WWTPs, whereas just a much lesser extent of 13C-incorporation by AOB and comammox Nitrospira was found in one WWTP. High-throughput sequencing with 13C-labeled DNA also showed the higher reads abundance of AOA than AOB and comammox Nitrospira. Nitrososphaera viennensis was the dominant active AOA, while Nitrosomonas oligotropha and Nitrosomonas europaea were identified as active AOB. The results obtained suggest that AOA, rather than AOB and comammox Nitrospira, dominate ammonia oxidation in WWTPs in cold season despite the numerical relationships of AOMs.

Changes in nitrogen related functional genes along soil pH, C and nutrient gradients in the charosphere

The interface between biochar and soil differs from both the bulk soil and the biochar itself, and has been termed the “charosphere”. However, a complete definition of the charosphere, including aspects of size, properties, functional reach and effects on soil processes, is still required. In this study, the distributions of functional genes related to the soil N cycle within the charosphere were investigated over a multi-sectional gradient. We found that concentrations of dissolved organic carbon (DOC), available phosphorus and exchangeable cations (Ca2+, Mg2+, K+) increased with proximity to the biochar surface (termed the ‘near charosphere’). Similarly, the abundance of bacterial amoA was greater in the near charosphere, while archaeal amoA abundance was relatively homogenous. This taxonomic asymmetry resulted in a shift in the predominant ammonia-oxidizers from ammonia-oxidizing bacteria (AOB) to ammonia-oxidizing archaea (AOA) in the far charosphere. This was associated with other factors such as decreasing pH and carbon availability with increasing distance from the biochar. Moreover, the ratio of nosZ/(nirS + nirK) genes also showed functionally asymmetry in the charosphere: increasing with increasing distance from the biochar. This is the first study to map spatial distributions of a set functional genes related to soil N cycling in the soil around biochar. This exploration into the underlying heterogeneity of biochar-affected mechanisms of N transformation provides new insight into the functional geometry of the charosphere.

Microbial community of nitrogen cycle-related genes in aquatic plant rhizospheres of Lake Liangzi in winter.

This study investigated the community structure of ammonia-oxidizing bacteria /archaea (AOB and AOA), as well as the effects of four aquatic plants (namely Ceratophyllum demersum, Hydrilla verticillata, Potamogeton crispus, and Nymphaea tetragona) rhizospheres on the abundance of AOB amoA, AOA amoA, anammox 16S rRNA, nirK, and nirS in Lake Liangzi, China. Phylogenetic analysis revealed that most AOB groups were Nitrosospira and Nitrosomonas, in which Nitrosospira was dominant. The AOA amoA were affiliated with two branches of classical sequences which belonging to Thaumarchaeota: water/sediments branch and soil/sediments branch. The abundance of AOA amoA in the rhizospheres of aquatic plants were higher than in the non-rhizosphere (p < 0.05), indicating that aquatic plants may promote the growth of AOA. However, the anammox 16S rRNA showed the opposite trend relative to AOA amoA (p < 0.05). Redundancy analysis (RDA) showed that the differences in abundance of AOB, AOA, anammox bacteria, and denitrifying bacteria are very likely related to the different contents of ammonia nitrogen (NH4 + -N), pH and dissolved oxygen (DO) and thus to the rhizosphere states of aquatic plants.

Maintenance of N cycling gene communities with crop-livestock integration management in tropical agriculture systems

Five different agricultural management systems and a forest fragment at two farms were investigated for effects on soil bacterial indicators. This study was conducted in southern Mato Grosso do Sul, Brazil, in January 2014, at two farms that incorporated integrated crop-livestock systems in Hapludox soil. Impacts of management were assessed through evaluation of functional bacterial communities using quantitative PCR (qPCR) of nitrogen cycling genes (amoA, nirK, and nosZ), PCR-DGGE of the nirK community composition, and by investigating relationships of the nirK community with soil properties. The nirK gene community showed that reference forest soil maintained relatively large nirK, nosZ, but small amoA gene abundances and large range weighted nirK richness (Rr). The introduction of pasture into crop-livestock integration management (inclusion of the second and third year of grazing within a crop-livestock integration system, CL-2 and CL-3, respectively) or the field in its first year of crop rotation after grazing pasture (CL-b) increased nosZ and amoA abundance. Three years of grazing pasture in crop-livestock integration (CL-a) increased nirK abundance, while multiple years of crop rotation in crop-livestock integration management systems increased soil OM and promoted a richer nirK community composition. The nirK community Rr that was not significantly different from the forest was observed in the second or third year of crop rotation after grazing (CL-c or CL-d, respectively) and (CL-3). In contrast, fields in pasture (CL-a, continuous pasture (CP)) and the first year of crop rotation after pasture (CL-b) had reduced Rr and functional organization curves, indicating communities less resilient to future stress. Management systems under integrated crop-livestock farming in tropical soil maintained a relatively diverse N cycling bacterial community, possibly promoting soil quality and N cycling processes.

Dicyandiamide has more inhibitory activities on nitrification than thiosulfate.

Dicyandiamide (DCD) and thiosulfates are two type of nitrification inhibitors (NIs) that have been widely used in agriculture to improve nitrogen (N) fertilizer use efficiency and mitigate negative effect of N on environment. Little information is available concerning the comparison of the efficacy of DCD and thiosulfate on N transformations in soil. The aim of this study was to compare the effects of DCD and thiosulfate (K2S2O3) on changes of NH4+-N, nitrification inhibition and N recovery in a latosolic red soil. An incubation experiment was conducted with four treatments of control (CK), N, N+DCD, and N+K2S2O3. Soil samples were collected periodically over 50 d to determine concentrations of mineral N, and the amoA gene abundance of ammonia monooxygenase (AMO) for ammonia-oxidizing bacteria (AOB) was estimated by qPCR after 10 d incubation. In the N treatment, 67.8% of the applied N as NH4+-N disappeared from the mineral N pool and only 2.7% and 30.8% of the applied N was accumulated as NO2--N and NO3--N, respectively. Addition of DCD and thiosulfate to the soil prevented NH4+-N disappearance by 63.0% and 13.6%, respectively. DCD suppressed the production of NO2--N by 97.41%, whereas thiosulfate increased accumulation of NO2--N by 14.6%. Application of N along with DCD and thiosulfate inhibited nitrification, respectively, by 72.6% and 33.1%, resulting in the delay of the nitrification process for 30 days and 10 days, respectively. Apparent N recovery in N treatment was 66.2%, which increased by 55.2% and 4.8% by DCD and thiosulfate, respectively. Numbers of AOB amoA gene copy was significantly inhibited by both DCD and thiosulfate, and the stronger inhibition induced by DCD than thiosulfate was recorded. Results indicated that both DCD and thiosulfate were effective inhibitors for NH4+-N oxidation, NO3--N production, mineral N losses and AOB growth. DCD showed a more pronounced effect on nitrification inhibition than thiosulfate.

The role of Chinese Milk Vetch as cover crop in complex soil nitrogen dynamics in rice rotation system of South China

The effect of Chinese Milk Vetch (CMV) residues as a cover crop on the performance of rice plants and nitrogen mobilization and mineralization in paddy soil was evaluated in a pot-culture experiment. Three treatments were included in the trial, i.e. without exogenous-N (Control or CK), urea fertilizer as the sole N-source (N) and urea plus CMV (NM). The results revealed higher amounts of total-N, inorganic-N, acid hydrolysable-N and non-acid hydrolysable-N in the soil under NM, followed by N and CK treatments at tillering, booting and maturity stages of rice. A similar trend was observed for various soil ammonia oxidizing bacteria, aerobic and anaerobic bacteria. Correlation coefficients exhibited a negative correlation of residual exogenous-15N with only amino acid nitrogen (P < 0.01). Moreover, low abundance of the key functional gene amoA in rice was found in CK treatment. From the results it can be concluded that the nitrogen from organic source can improve the availability of total-N, inorganic-N and NH4 in the soil, especially at the later stages of rice growth.

Effects of Biochar on Nitrous Oxide Fluxes and the Abundance of Related Functional Genes from Agriculture Soil in the North China Plain

To explore the effect and mechanism of biochar application in reducing nitrous oxide (N2O) content in agricultural soil, from March 27 to June 5 2015, pot experiments were conducted to study the effects of biochar application rates (CK, C1:5%, C2:10%, C3:15%, and C4:30%) (mass fraction) on soil N2O fluxes and the functional marker genes ammonia monooxygenase (amoA), nirK, nirS, and nosZ, which are responsible for nitrification and denitrification. The results revealed the following. ①The application of low doses of biochar (5%) promoted N2O emission. The application of middle and high doses of biochar reduced N2O emission. Furthermore, the application of biochar (15%) was found to be the best practice to reduce N2O emission. ② At the beginning of the experiment, biochar had a significant effect on the abundance of soil amoA and denitrification bacteria gene. Furthermore, the abundance of AOA and nirS had a significant positive correlation with the biochar rate, and the abundance of nirK gene and biochar rate were significant. There was a significant negative correlation between AOB and nosZ gene abundance and biochar rate. At the end of the experiment, AOA abundance correlated negatively with biochar rate, while there was a significantly positive relationship between AOB abundance and biochar rate. ③ At the beginning of the experiment, the N2O fluxes exhibited a significant negative correlation with AOA and nirS gene, indicating that N2O production was controlled by the abundance of AOA and nirS gene under high soil moisture content. At the end of the experiment, there was a significant positive correlation between N2O flux and nosZ gene, indicating that the production of N2O was regulated by the abundance of nosZ gene under low soil water content. The results of this study showed that the application of biochar altered the abundance of amoA and denitrification bacteria genes, and reduced N2O emission. These results provide a theoretical basis for a rational application of biochar in farmland.

Evaluating toxicity of 1-octyl-3-methylimidazolium hexafluorophosphate to microorganisms in soil

Ionic liquids (ILs) were widely applied because of their excellent properties. The present investigation studied the toxicity of the IL 1-octyl-3-methylimidazolium hexafluorophosphate ([Omim]PF6) to the soil microbial population and community diversity with dose (1.0, 2.0, 4.0, 6.0, and 8.0 mg kg−1) and exposure time (7, 10, and 13 d). The results show the IL was stable during the entire experimental period. The Biolog-ECO plate results indicated that the average well color development (AWCD) in the 6.0 and 8.0 mg kg−1 treatments was lower than these in the other treatments. The diversity indices of the Biolog analysis were significantly reduced. The abundance of the ammonia-oxidizing archaea (AOA-) and the ammonia-oxidizing bacteria (AOB-) ammonia monooxygenase (amoA) genes was measured by the real-time polymerase chain reaction (RT-PCR). In the treatments of 4.0, 6.0 and 8.0 mg kg−1, the abundance of amoA genes of the AOA- and AOB- were inhibited by IL [Omim]PF6.

Impact of tetracycline on the performance and abundance of functional bacteria of a lab-scale anaerobic-aerobic wastewater treatment system

The occurrence of various antibiotics in wastewater treatment systems continues to arouse extensive attention. However, the effects of low concentration of antibiotics on wastewater treatment performance and the related functional bacteria, especially under long-term operation, remain largely unknown. In this study, a lab-scale anaerobic-aerobic system was established to evaluate the impacts of 5 mg l−1 tetracycline on the performance of a lab-scale wastewater treatment system and the abundance of the related functional bacteria. The results indicated that Tc exposure had little effect (p > 0.05) on the efficiency of COD removal during the whole period of 200 days, but significantly decreased ammonia removal (p < 0.05) and accelerated sludge bulking deterioration. Although the core bacterial communities and the abundance of amoA genes in the activated sludge were not affected, the growth of Nitrospira was inhibited (p < 0.05), and Sphaerotilus was promoted by tetracycline exposure. The results of this study provide important references for the maintenance of wastewater treatment systems.

Microbial pathways for nitrous oxide emissions from sheep urine and dung in a typical steppe grassland

The aim of this study was to determine the responses of nitrifiers and denitrifiers to understand microbial pathways of nitrous oxide (N2O) emissions in grassland soils that received inputs of sheep excreta. Sheep dung and synthetic sheep urine were applied at three different rates, simulating a single, double, or triple overlapping of urine or dung depositions in the field. Quantitative PCR and high-throughput sequencing were combined with process-based modeling to understand effects of sheep excreta on microbial populations and on pathways for N2O production. Results showed that emissions of N2O from urine were significantly higher than from dung, ranging from 0.12 to 0.78 kg N2O-N ha−1 during the 3 months. The N2O emissions were significantly related to the bacterial amoA (r = 0.373, P < 0.001) and nirK (r = 0.614, P < 0.001) gene abundances. It was autotrophic nitrification that dominated N2O production in the low urine-N rate soils, whereas it was denitrification (including nitrifier denitrification and heterotrophic denitrification) that dominated N2O production in the high urine-N rate soils. Nitrifier denitrification was responsible for most of the N2O emissions in the dung-treated soils. This study suggests that nitrifier denitrification is indeed an important pathway for N2O emissions in these low fertility and dry grazed grassland ecosystems.

Field-aged biochar stimulated N2O production from greenhouse vegetable production soils by nitrification and denitrification

Evidence suggests that biochar is among ideal strategies for climate change mitigation and sustainable agriculture. However, the effects of soil aging on the physicochemical characteristics of biochar and nitrous oxide (N2O) production remain elusive. We set up a microcosm experiment with two greenhouse vegetable production (GVP) (alkaline and acid) soils by using the 15N tracing technique and quantitative polymerase chain reaction (qPCR) to investigate the mechanisms of N2O production as affected by fresh (FB) and aged biochar (AB) amendment. The results showed that AB increased the specific surface area, organic C, ammonium sorption capacity and cation exchange capacity, whereas decreased the pore size and pH relative to the FB. Results also demonstrated that FB effectively decreased N2O emissions from both soils while it enhanced the abundance of nirK and nosZI genes in alkaline soil and reduced the abundance of ammonia-oxidizing bacteria (AOB) amoA and increased nirK and nosZII genes in acid soil. In contrast, AB significantly stimulated nitrification and denitrification in both soils and thus significantly increased the N2O emissions by 43–78%. Furthermore, AB induced increases in ammonia-oxidizing archaeal (AOA) amoA and nirK gene abundances in alkaline soil and fungal nirK gene abundances in acid soil. These results suggest that AB may not be suitable for the mitigation of soil N2O emissions in GVP soils thus improving our understanding of the potential mechanism of biochar in N2O emissions.

Short-term responses of soil nitrogen mineralization, nitrification and denitrification to prescribed burning in a suburban forest ecosystem of subtropical Australia

As an anthropogenic disturbance, prescribed burning may alter the biogeochemistries of nutrients, including nitrogen (N) cycling, in forest ecosystems. This study aimed to examine the changes in N mineralization, nitrification and denitrification rates following prescribed burning in a suburban forest located in subtropical Australia and assess the interactive relationships among soil properties, functional gene abundances and N transformation rates. After a prescribed burning event, soil pH value increased, but soil labile carbon and mineral N contents decreased. Net N mineralization rates, potential nitrification rates and ammonium-oxidizing archaea and bacteria (AOA and AOB) amoA gene abundances in the soils all increased after 3 months of the prescribed burning. However, the abundances of different functional genes related to denitrification changed differently after the prescribed burning. The net N mineralization rates could be best described by soil abiotic properties, rather than functional gene abundances. In contrast, potential denitrification rates were positively related to soil nirK gene abundances. Potential nitrification rates could be influenced by both soil chemical and microbial properties. The results revealed that the prescribed burning might increase N mineralization and nitrification rates in the forest soil.

Effects of nitrification inhibitor and herbicides on nitrification, nitrite and nitrate consumptions and nitrous oxide emission in an Australian sugarcane soil

This study evaluated the impacts of a nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP) and herbicides (atrazine and glyphosate) on nitrification, gross nitrite, and nitrate (NO2−-N + NO3−-N) consumption rate, nitrous oxide (N2O) emission, and abundances of microbial functional genes related to nitrogen (N) cycling in an Australian sugarcane soil. The experiment included four treatments: blank control (CK), DMPP application (NI), atrazine application (ATR), and glyphosate application (GLY). All treatments received (NH4)2SO4 at 50 mg N kg−1 dry soil and KNO3 at 50 mg N kg−1 dry soil and were incubated initially at 55% of water holding capacity (WHC) for 7 days and subsequently at 75% WHC for another 7 days (K15NO3 with 5 atom% 15N added at the beginning of each stage). Compared with the CK treatment, DMPP application significantly decreased N2O emissions throughout the incubation, while atrazine or glyphosate application significantly inhibited N2O emissions only during the 4–7-day period. DMPP application also decreased ammonium-oxidizing bacteria (AOB) amoA gene abundances, gross NO2−-N + NO3−-N consumption rates at 55 and 75% WHC, and nirS and nirK gene abundances of denitrifiers at 75% WHC. The atrazine and glyphosate applications decreased the gross nitrification and NO2−-N + NO3−-N consumption rates, abundances of both ammonium-oxidizing archaea (AOA) and AOB amoA genes at 55 and 75% WHC, and abundances of functional genes related to different reactions of the denitrification during the incubation. These results suggested that DMPP, atrazine, and glyphosate could decrease soil gross nitrification and denitrification rates perhaps by inhibiting microbial functional gene abundances and that application of DMPP could effectively reduce N2O emissions in the sugarcane cropping soil.

Different Height Forms of Spartina alterniflora Might Select Their Own Rhizospheric Bacterial Communities in Southern Coast of China.

In the southernmost part of coast of China, two height forms of Spartina alterniflora, tall and short, have invaded Leizhou Peninsula within the last decade. However, the effect of different height forms of Spartina alterniflora on plant-microbe interaction has not been clarified. Here, the community structures of rhizosphere bacteria and the abundance of N- and S-cycling functional genes associated with selected S. alterniflora were investigated in the field and a common garden. The community structure of tall-form S. alterniflora was distinct from short-form S. alterniflora at OTU level in the field, even after transplantation into a common garden. The abundance of bacterial amoA, nirS, and nosZ in tall S. alterniflora was significantly greater than those in short S. alterniflora in the field; however, this difference disappeared in a 1-year common garden experiment. These results suggested that compared with the tall-form S. alterniflora, the rhizosphere of short-form S. alterniflora harbored fewer nitrification-denitrification related microorganisms, which might benefit from conserving N in an N limited habitat. Together, our results suggested that tall- and short-form S. alterniflora can host their specific rhizosphere microbial communities and had different strategies of N usage via selecting the composition of rhizosphere bacterial assemblages, which in turn might determine the growth and invasiveness of S. alterniflora in its introduced range.