Yellow clay paddy soil (Oxisols) is a low-yield soil with low nitrogen use efficiency (NUE) in southern China. The nitrification inhibitor nitrapyrin (2-chloro-6- (tricholoromethyl)-pyridine, CP) has been applied to improve NUE and reduce environmental pollution in paddy soil. However, the effects of nitrapyrin combined with nitrogen fertilizers on ammonia oxidizers in yellow clay paddy soil have not been examined.
Materials and methodsA randomized complete block design was set with three treatments: (1) without nitrogen fertilizer (CK), (2) common prilled urea (PU), and (3) prilled urea with nitrapyrin (NPU). Soil samples were collected from three treatments where CK, PU, and NPU had been repeatedly applied over 5 years. Soil samples were analyzed by quantitative PCR and 454 high-throughput pyrosequencing of the amoA gene to investigate the influence of nitrapyrin combined with nitrogen on the abundance and community structure of ammonia oxidizers in yellow clay paddy soil.
Results and discussionThe potential nitrification rate (PNR) of the soil was significantly correlated with the abundances of both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Application of urea significantly stimulated AOA and AOB growth, whereas nitrapyrin exhibited inhibitory effects on AOA. Phylogenetic analysis showed that the most dominant operational taxonomic units (OTUs) of AOA and AOB were affiliated with the Nitrosotalea cluster and Nitrosospira cluster 12, respectively. AOA and AOB community structures were not altered by urea and nitrapyrin application.
ConclusionsNitrogen fertilization stimulated nitrification and increased the population sizes of AOA and AOB. Nitrapyrin affected the abundance, but not community structure of ammonia oxidizers in yellow clay soil. Our results suggested that nitrapyrin improving NUE and inhibiting PNR was attributable to the inhibition of AOA growth.
相似文献Microbial nitrification plays an important role in nitrogen cycling in ecosystems. Nitrification is performed by ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) including complete ammonia oxidizers. However, the relative importance of nitrifiers in autotrophic nitrification in relation to soil pH is still unclear.
Materials and methodsCombining DNA-based stable isotope probing (SIP) and molecular biological techniques, we investigated the abundance, structure, and activity of AOA, AOB, and NOB along a pH-gradient (3.97–7.04) in a vegetable cropped soil.
Results and discussionWe found that AOA abundance outnumbered AOB abundance and had a significantly negative relationship with soil pH. The abundances of NOB Nitrospira 16S rRNA, nxrB gene, and Nitrobacter nxrA gene were affected by soil pH. Incubation of soil with 13CO2 and DNA-SIP analysis demonstrated that significant 13CO2 assimilation by AOA rather than by AOB occurred in the acidic soils, whereas the labeled 13C level of AOA was much less in the neutral soil than in the acidic soils. There was no evidence of 13CO2 assimilation by NOB except for Nitrobacter with NxrB gene at pH 3.97. Phylogenetic analysis of AOA amoA gene in the 13C- and 12C-labeled treatments showed that the active AOA mainly belonged to Nitrososphaera in the acidic soils.
ConclusionsThese results suggested that the main performer of nitrification was AOA in the acidic soils, but both AOA and AOB participated in nitrification in the neutral soil with low nitrification activity. NOB Nitrospira and Nitrobacter did not grow in the soils with pH 4.82–7.04 and other populations of NOB were probably involved in nitrite oxidation in the vegetable cropped soil.
相似文献The iron redox cycle is closely tied to the fate of carbon in terrestrial ecosystems, especially paddy soils. Varies diurnally and seasonally, light—the crucial environmental factor—may be a fundamental factor elucidating temporal and spatial variabilities of carbon-containing gases emission. The role of sunlight in the iron-mediated carbon cycle, however, has not been fully elucidated. We conduct this study to test the role of light in the iron-mediated carbon cycling.
Materials and methodsIn this study, we conducted anaerobic incubation experiments of a calcareous paddy soil in serum vials under alternating dark and light conditions. The dynamic evolution of the carbon and iron contents was evaluated by measuring the CO2, CH4, and O2 concentrations in the headspace of the vials, as well as the water-soluble inorganic carbon, microbial biomass carbon, and HCl-extractable ferrous iron contents in soil slurries. We also analyzed the soil microbial community structure by high-throughput 16S rRNA gene sequencing.
Results and discussionThe results highlighted the positive correlation between carbon mineralization and ferric iron reduction under dark conditions. Under light conditions, however, ferrous iron was oxidized by the O2 generated via oxygenic photosynthesis of phototrophic bacteria such as Cyanobacteria, along with a decreased production of CO2, CH4, and water-soluble inorganic carbon. The abundance of Cyanobacteria positively correlated to O2 levels and MBC content significantly. Light-induced periodic variations in the redox conditions facilitated carbon fixation in microbial biomass and up to 31.79 μmol g?1 carbon was sequestrated during 30 days light incubation.
ConclusionsThese results indicate that light inhibits the emission of carbon-containing greenhouse gases associated with the iron redox cycle in calcareous paddy soil. Assimilation of inorganic carbon by phototrophs may responsible for the inhibition of carbon mineralization. Our study suggests that procedures allowing more light to reach the soil surface, for instance, reducing the planting density, may mitigate greenhouse gas emissions and promote carbon sequestration in paddy soils.
相似文献Paddy fields are an important source of nitrous oxide (N2O) emission. The application of biochar or the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to paddy soils have been proposed as technologies to mitigate N2O emissions, but their mechanisms remain poorly understood.
MethodsAn experiment was undertaken to study the combined and individual effects of biochar and DMPP on N2O emission from a paddy field. Changes in soil microbial community composition were investigated. Four fertilized treatments were established as follows: fertilizer only, biochar, DMPP, and biochar combined with DMPP; along with an unfertilized control.
ResultsThe application of biochar and/or DMPP decreased N2O emission by 18.9–39.6% compared with fertilizer only. The combination of biochar and DMPP exhibited higher efficiency at suppressing N2O emission than biochar alone but not as effective as DMPP alone. Biochar promoted the growth of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), while DMPP suppressed AOB and increased AOA. Applying biochar with DMPP reduced the impact of DMPP on AOB. The nirS-/nirK- denitrifiers were decreased and nosZ-N2O reducers were increased by DMPP and the combination of DMPP and biochar. The abundance of the nirK gene was increased by biochar at the elongation and heading stages of rice development. Compared with fertilizer only, the application of biochar and/or DMPP promoted the abundance of nosZ genes.
ConclusionThese results suggest that applying biochar and/or DMPP to rice paddy fields is a promising strategy to reduce N2O emissions by regulating the dynamics of ammonia oxidizers and N2O reducers.
相似文献Purpose
The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 ?) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.Materials and methods
Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.Results and discussion
The three soils varied significantly in the microbial biomass C (858 to 542 μg C g?1 soil) and biomass N (63 to 28 μg N g?1), protease (361 to 694 μg tyrosine g?1 soil h?1) and deaminase (4.3 to 5.6 μg NH4 + g?1 soil h?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?109 to 2.77?×?109 g?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?107 to 3.01?×?108 g?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.Conclusions
These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities. 相似文献Crop straw and biochar application can potentially increase carbon sequestration and lead to changes in the microbial community in agricultural soils. Sequestration of CO2 by autotrophic microorganisms is key to biogeochemical carbon cycling in soil ecosystems. The effects of straw and its biochar, derived from slow pyrolysis, on CO2 fixation bacteria in sandy soils, remain unclear. Therefore, this study compared the response of abundance and community of CO2 fixation bacteria to the two straw application methods in a sandy agricultural soil. The overall aim of the study was to achieve an efficient use of straw residues for the soil sustainablility.
Materials and methodsWe investigated the soil organic carbon content and autotrophic bacteria over four consecutive years (2014–2018) in a field experiment, including the following four treatments: whole maize straw amendment (S), whole maize straw translated biochar amendment (B), half biochar and half straw amendment (BS), and control (CK) without straw or biochar amendment. The autotrophic bacterial abundance and community structure were measured using molecular methods of real-time PCR, terminal restriction fragment length polymorphisms (T-RFLP), and a clone library targeting the large subunit gene (cbbL) of ribulose-1,5-bisphosphate carboxylase/oxygenase.
Results and discussionThe results showed that the content of soil total organic carbon (TOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) in B, S, and BS treatments was significantly increased compared with the CK treatment. Soil TOC and available potassium (AK) in the B treatment significantly increased by 15.4% and 23.3%, respectively, but soil bulk density, DOC, and MBC significantly decreased by 8.5%, 10.6%, and 14.5%, respectively, compared with the S treatment. The abundance of the cbbL gene as well as of the bacterial 16S rRNA gene increased significantly in straw or biochar application treatments as compared to the CK treatment. The B treatment, but not the BS treatment, significantly increased the cbbL gene abundance when compared to the S treatment. No significant differences were observed in the bacterial 16S rRNA gene abundance among the three straw or biochar applications. The application of straw biochar could increase the diversity of the autotrophic bacteria, which also altered the overall microbial composition. Physicochemical properties of the soil, such as soil pH, SOC, and bulk density, can help explain the shift in soil microbial composition observed in the study.
ConclusionsTaken together, our results suggest that straw biochar, rather than straw application, leads to an increase in the abundance and diversity of CO2-fixing bacteria, which would be advantageous for soil autotrophic CO2 fixation.
相似文献This investigation assessed the responses of soil fertility, enzyme activity, and microbial community diversity to soil texture and land use type.
Materials and methodsThe tested soils included five soil textures (sandy loam, medium loam, heavy loam, light clay, and medium clay soils) with two land use types (uncultivated and paddy soils) in the coastal zone of Zhejiang Province, China.
Results and discussionSoil texture had a significant effect on soil pH, electrical conductivity (EC), organic carbon (OC), total nitrogen (TN), available nitrogen (AN), phosphorus (AP) and potassium (AK), catalase and protease activities, total phospholipid fatty acids (PLFAs), bacterial and actinomycetes PLFAs, and microbial diversity (MD). The clay content was significantly positively correlated to soil EC, OC, TN, AN, AP, AK, catalase activity, total PLFAs, bacterial and actinomycetes PLFAs, and MD but significantly negatively associated with soil pH and protease activity. Land use type also had significantly influenced soil pH, EC, OC, TN, AN, AP, AK, catalase, protease and urease activities, total PLFAs, bacterial, actinomycetes, and fungal PLFAs, and MD. The paddy soil had higher OC, TN, AN, AP, catalase, protease and urease activities, total PLFAs, bacterial and actinomycetes PLFAs, and MD but lower soil pH, EC, and AK than the uncultivated soil. The interaction with soil texture and land use type had significantly affected soil pH, EC, OC, TN, AN, AP, AK, catalase and protease activities, total PLFAs, bacterial and actinomycetes PLFAs, and MD.
ConclusionsSoil texture and land use type could be considered important factors in improving soil fertility, enzyme activity, and microbial diversity in coastal saline soils.
相似文献Ammonia oxidation is the limiting step in soil nitrification and critical in the global nitrogen cycle. The discovery of ammonia-oxidizing archaea (AOA) has improved our knowledge of microbial mechanisms for ammonia oxidation in complex soil environments. However, the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation remain unclear.
Materials and methodsIn this study, through large geographical scale sampling in China, totally nine samples representing various types of arable land soils were selected for analyzing the ammonia oxidation activity. The AOA and AOB activities were separately determined by using the dicyandiamide and 1-octyne inhibition method. High-throughput pyrosequencing and DNA stable-isotope probing (DNA-SIP) analysis were applied to investigate the distribution and activity of Candidatus Nitrosocosmicus franklandus in the arable land soils.
Results and discussionIn this study, AOA abundance (3.2?×?107–3.4?×?109 copies g?1) and activity (0.01–1.33 mg N kg?1 dry soil day?1) were evaluated for nine selected arable land soils and accounted for 4–100% of ammonia oxidation. By separately determining AOA and AOB rates, we observed that archaeal ammonia oxidation dominated the ammonia oxidation process in six soils, revealing a considerable contribution of AOA in ammonia oxidation in arable land soils. Based on high-throughput pyrosequencing analysis, the AOA species Ca. N. franklandus with relatively low abundance (0.6–13.5% in AOA) was ubiquitously distributed in all the tested samples. Moreover, according to the DNA-SIP analysis for Urumqi sample, the high activity and efficiency of Ca. N. franklandus in using CO2 suggests that this species plays an important role in archaeal ammonia oxidation in arable land soils.
ConclusionsThrough determining the AOA activity and analyzing the potential predominant functional AOA species, this study greatly improves our understanding of ammonia oxidation in arable land soils.
相似文献The discovery of comammox Nitrospira being capable of complete oxidising ammonia to nitrate radically challenged the conventional concept of two-step nitrification. However, the response of comammox Nitrospira to nitrification inhibitors (NIs) and their role in soil nitrification remain largely unknown, which has hindered our ability to predict the efficiency of NIs in agroecosystems.
Materials and methodsWe evaluated the effect of four NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), 3,4-dimethylpyrazole phosphate (DMPP), allylthiourea (ATU) and dicyandiamide (DCD) on the growth of comammox Nitrospira, ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) in two pasture and arable soils.
Results and discussionThe amendment of nitrogen fertiliser significantly increased soil nitrate concentrations over time, indicating a sustaining nitrification activity in both soils. The addition of all the four NIs effectively reduced the production of nitrate in both soils, but to varying degrees during incubation. The abundances of comammox Nitrospira clade A were significantly increased by addition of nitrogen fertilisers and significantly impeded by the four NIs in the pasture soil, but their abundances were only remarkably hindered by nitrapyrin in the arable soil. All the four NIs obviously inhibited the AOB abundances in both soils. Except for DMPP, the other three NIs effectively suppressed the AOA abundances in both soils.
ConclusionsWe provided new evidence that growth of comammox Nitrospira clade A can be stimulated by nitrogen fertilisers and inhibited by various nitrification inhibitors, suggesting their potential role in nitrification of agricultural soils.
相似文献