Denitrification In Paddy Soil Research Articles

Denitrification contributes to N2O emission in paddy soils.

Denitrification is vital to nitrogen removal and N2O release in ecosystems; in this regard, paddy soils exhibit strong denitrifying ability. However, the underlying mechanism of N2O emission from denitrification in paddy soils is yet to be elucidated. In this study, the potential N2O emission rate, enzymatic activity for N2O production and reduction, gene abundance, and community composition during denitrification were investigated using the 15N isotope tracer technique combined with slurry incubation, enzymatic activity detection, quantitative polymerase chain reaction (qPCR), and metagenomic sequencing. Results of incubation experiments showed that the average potential N2O emission rates were 0.51 ± 0.20 μmol⋅N⋅kg-1⋅h-1, which constituted 2.16 ± 0.85% of the denitrification end-products. The enzymatic activity for N2O production was 2.77-8.94 times than that for N2O reduction, indicating an imbalance between N2O production and reduction. The gene abundance ratio of nir to nosZ from qPCR results further supported the imbalance. Results of metagenomic analysis showed that, although Proteobacteria was the common phylum for denitrification genes, other dominant community compositions varied for different denitrification genes. Gammaproteobacteria and other phyla containing the norB gene without nosZ genes, including Actinobacteria, Planctomycetes, Desulfobacterota, Cyanobacteria, Acidobacteria, Bacteroidetes, and Myxococcus, may contribute to N2O emission from paddy soils. Our results suggest that denitrification is highly modular, with different microbial communities collaborating to complete the denitrification process, thus resulting in an emission estimation of 13.67 ± 5.44 g N2O⋅m-2⋅yr-1 in surface paddy soils.

Effects of Drying-Rewetting Cycles on Ferrous Iron-Involved Denitrification in Paddy Soils

Soil moisture status has an important effect on the process of denitrification in paddy soils. However, it is unclear how it affects the ferrous iron-involved denitrification. Here, the influence of drying-rewetting cycles on ferrous iron-involved denitrification in paddy soil were studied with batch experiments. The dynamics of nitrate, ammonia, Fe2+, Fe3+ and total organic carbon (TOC), as well as nitrous oxide (N2O) were investigated using the iron-rich paddy soil in Jiangxi province, South China. Results demonstrated that the denitrification rate dropped while ammonia nitrogen content (NH4+-N) showed a rapid accumulation in the drying period. In the rewetting period, organic carbon played two-side roles. Organic carbon and ferrous iron together provided electron donors to denitrification, and organic carbon simultaneously reduced ferric iron under anaerobic environment. There were complex interactions among organic carbon, nitrate and Fe2+/Fe3+ under drying-rewetting cycles. Soil rewetting led to denitrification flush, especially after a moderately long drying period, while excessively frequent drying-rewetting alternation was not favorable to nitrate denitrification.

Investigation of Fe(II) and Mn(II) involved anoxic denitrification in agricultural soils with high manganese and iron contents

Soil denitrification rates and the roles Mn(II) and Fe(II) played as alternative electron donors were investigated by performing anoxic incubation experiments, using agricultural soils from Guangxi Autonomous Region, South China. The dynamic of Mn(II) and Fe(II), electron contributions of Mn(II) and Fe(II) to denitrification, potential denitrification capacity, and gaseous-N composition were investigated. The results indicated that Mn(II) and Fe(II) act as electron donors during the denitrification of paddy soils with high Mn and Fe contents. Coupling of denitrification and Fe(II) oxidation and coupling of denitrification and Mn(II) oxidation was found in paddy soils from the villages of Xialei. The maximum electron contributions of Mn(II) and Fe(II) to denitrification were similar, both reaching 18%, although the total Mn content was lower than the total Fe content. On the contrary, the roles and contributions of Mn(II) and Fe(II) to denitrification in soils from upland fields were not proved, even though all the studied agricultural soils had high Mn and Fe contents. The results suggested that Mn(II) is an important but previously ignored electron donor for denitrification and that Mn(II) plays a vital role in denitrification in paddy soils.

Nitrification and urease inhibitors improve rice nitrogen uptake and prevent denitrification in alkaline paddy soil

Increasing evidence indicates that nitrification is a vital factor in crop growth and nitrous oxide emission. Nitrification and urease inhibitors have been demonstrated to be effective in inhibiting the nitrification process and are widely used as fertilizer additives in agricultural soils. However, the effects of these inhibitors on rice N uptake and N2O production through denitrification in paddy soils remain unclear. In the present work, we compared the influences of nitrification inhibitors dicyandiamide (DCD), nitrapyrin (2-chloro-6-(trichloromethyl) pyridine; NP) and N-(n-butyl) thiophosphoric triamide (NBPT) on rice growth, the fate of urea nitrogen (N), and the abundances and activities of ammonia oxidizers and denitrifiers. The fate of urea N was determined by the 15N isotope labeling technique, and the abundances of ammonia oxidizers and denitrifiers were determined using qPCR. All three inhibitors improved rice growth mainly due to the increase in urea N use efficiency. Urea N uptake was negatively correlated with nitrification. The growth of ammonia-oxidizing bacteria (AOB), important in nitrification, was directly blocked by DCD. Additionally, NP and NBPT impeded the growth of ammonia-oxidizing archaea (AOA). In addition, NP significantly increased the microbial biomass to promote more residual urea N in soil and increased soil N transformation. NBPT significantly inhibited urea hydrolysis indirectly affecting nitrification. All three inhibitors decreased the potential denitrification rate (PDR) at the rice heading stage but had little effect on the denitrifier gene abundance except for nitrapyrin, which decreased the nirK gene abundance. DCD and NBPT may reduce the denitrification activity by decreasing the denitrification substrate (NO3−) concentration. These results suggest that DCD, NP and NBPT have a beneficial effect on improving rice N uptake and have the potential to reduce N2O generation through denitrification.

Denitrification in paddy soil as a cooperative process of different nitrogen oxide reducers, revealed by metatranscriptomic analysis of denitrification-induced soil microcosm

ABSTRACT Denitrification in paddy soils is an environmentally important reaction, which reduces leaching or emission of nitrogen pollutants. This reaction has long been considered to be driven by typical denitrifiers mostly belonging to Alpha-, Beta-, and Gammaproteobacteria. Our recent metatranscriptomic analysis of rice paddy field soil suggested that paddy soil denitrification is a cooperative process of different nitrogen oxide reducers, i.e., NO2 −, NO, and N2O reducers. However, it was not clear whether denitrification actually occurred in the soil samples examined, which was not easy to confirm under field conditions. Therefore, we carried out this study (1) to establish a soil microcosm with the steady activity of denitrification, and (2) to identify microbial communities, which drive each step of denitrification in the soil microcosm by metatranscriptomic analysis. As a result, a chemostat-type soil microcosm with steady denitrification activity was successfully established. Metatranscriptomic analysis of the denitrification-induced soils, together with supportive PCR-based clone library analysis, indicated that the community compositions of microbial drivers at each step of denitrification are different from each other. The results verified our above-mentioned suggestion of denitrification in paddy soil being a cooperative process of different nitrogen oxide reducers. Microbial communities of the cooperative denitrification in paddy soil might be established, and might have advantages to eliminate/detoxify microbiologically and/or chemically generated nitrogen oxides smoothly under changing paddy soil environments.

Response of denitrification in paddy soils with different nitrification rates to soil moisture and glucose addition

Denitrification is one of the most important N loss pathways in paddy soil. The nitrification rate is a key natural feature for controlling denitrification N loss in paddy soil. However, the relationship between nitrification and denitrification under different conditions in paddy soil remains unknown. By using 15N tracing, we investigated the response of denitrification loss to soil moisture and glucose addition in six paddy soils, whose net nitrification rates ranged from 0.36 mg N kg−1 day−1 to 5.72 mg N kg−1 day−1. The soils were amended with or without glucose to simulate root exudates at rates of 100 mg kg−1 of soil and incubated under either 60% water holding capacity (WHC) or flooded (2 cm depth) at 25 °C for 15 days. Denitrification loss was calculated by the unrecovered 15NH4+. The results showed that the soil nitrification rate significantly affected the N recovery form and denitrification loss of the applied 15N. NH4+ was the main recovered N form of the applied 15N in soil with a low nitrification rates. Denitrification losses were higher in the high nitrification rate soil than soil with low nitrification rate in all treatments. The correlation between denitrification and nitrification rates was well fit by Michaelis-Menten kinetics during the incubation, irrespective of soil moisture and glucose addition, and the R2 ranged from 0.801 to 0.977 (P < 0.05). Glucose addition did not stimulate denitrification under either 60% WHC or flooded conditions. The results showed that nitrification rate, rather than labile organic supply, controlled denitrification in paddy soil.

Effect of rice straw and/or nitrogen fertiliser inputs on methanogenic archaeal and denitrifying communities in a typical rice paddy soil

ABSTRACTTo understand better the microbial functional populations which are involved in methanogenesis and denitrification in paddy soils with rice straw (RS) and/or nitrogen fertiliser (potassium nitrate, N) application, the dynamics of methanogens and the denitrifying community were monitored simultaneously during the incubation period. The results show that the community structure of methanogens remained relatively stable among treatments based on 16S rDNA analysis, but fluctuated based on 16S rRNA. The Methanocellaceae and Methanosarcinaceae dominated all treatments at 16S rDNA and 16S rRNA level, respectively. RS+N increased the relative abundance of Methanosaetaceae at the 16S rRNA level, while there was an increasing trend in that Methanomicrobiaceae following RS addition at the 16S rDNA level. RS and/or N did not significantly change the diversity of methanogens targeting both 16S rDNA and 16S rRNA. RS and RS+N increased copy numbers of methanogens targeting both 16S rDNA and 16S rRNA analyses. The community structure and abundance of nirS and nosZ-containing denitrifiers, and the diversity of nirS-containing denitrifiers was significantly altered only by the N treatment. These results indicate that the community structure, diversity and abundance of methanogens respond differently to RS addition at the 16S rDNA and 16S rRNA levels.

Evidence for nitrification ability controlling nitrogen use efficiency and N losses via denitrification in paddy soils

For understanding the effects of nitrification ability on nitrogen (N) use efficiency and N losses via denitrification in paddy soils under flooding conditions, six paddy soils with different nitrification activities were sampled from various sites of China and a pot experiment was conducted. Rice plants at tillering stage were transplanted into pots and harvested 7.5 days after transplanting, 15N-(NH4)2SO4 was applied 2.5 days after rice transplanting under continuously flooding conditions. The N losses by denitrification were determined by the unrecovered 15N applied as 15NH4 + and the N use efficiency (NUE) was calculated by 15N taken up by rice plants. Plant height (from 33.8 to 37.3 cm) and biomass (from 1.07 g pot−1 to 1.52 g pot−1) increased significantly with the native NH4 + concentration in the studied soils (P < 0.01). The NUE decreased, whereas the N losses via denitrification increased due to the increase in the nitrification rate of soils determined at 60% water holding capacity (P < 0.05). The results implied that the nitrification activity of paddy soils is a key factor in controlling NUE and N losses via denitrification.

Iron oxidation affects nitrous oxide emissions via donating electrons to denitrification in paddy soils

Paddy soils are important source of nitrous oxide (N2O), which production is mainly regulated through redox processes and electron transfer. Ferrous iron [Fe(II)] oxidation coupled to denitrification is ubiquitous in paddy soils, which could affect N2O production via donating electrons to denitrification. To clarify the effects of Fe(II) oxidation on denitrification and N2O emissions, a flooding experiment was conducted in two paddy soils with contrasting Fe(II) levels. The soil with high Fe(II) concentration emitted less N2O than did the other soil with low Fe(II) concentration. Nitrate addition decreased Fe(II) concentration and stimulated N2O production in both soils, suggesting that Fe(II) oxidation is coupled to denitrification. The stoichiometry of electron transfer between nitrate reduction and Fe(II) oxidation demonstrated that the percentage of electrons contributed by Fe(II) to denitrification accounted for 16.2% and 32.9%, and the ratios of the electrons donated by Fe(II) to the electrons accepted by nitrate for N2O production were 43.7% and 130.7% in the two soils with low and high Fe(II) concentration, respectively. The ratio beyond 100% implies that the electrons donated by high Fe(II) concentration exceed the electron demand for N2O production, which lead to the further reduction of N2O to N2. In conclusion, Fe(II) oxidation coupled to denitrification affects N2O emissions via electron donation, and Fe(II) in a high concentration bears great potential for efficient denitrification and low N2O emissions from paddy soils.

Denitrification and its product composition in typical Chinese paddy soils

Denitrification and its products composition were evaluated in four typical Chinese paddy soils with pH (H2O) ranging from 4.80 to 8.29 after application of 50 or 100 mg kg−1 soil K15NO3 and subsequent anaerobic incubation. Denitrification rates, which were indicated by nitric oxide (NO), nitrous oxide (N2O), and dinitrogen gas (N2) production, significantly varied among different paddy soils. The denitrification rates of the neutral and alkaline paddy soils were 2.6 to 16.6 times higher, respectively, than those of acidic paddies. Furthermore, denitrification in paddy soils could produce end products other than N2, and the product composition depended on the paddy soil type. The percentage of total N gases (NO + N2O + N2) present as N2O was negatively and linearly correlated with denitrification rate (P < 0.05). Soil pH and C/N showed positive effects on denitrification rate (r = 0.800 and r = 0.781, respectively, P < 0.05 for both), but negative effects on the percentage of total N gases present as N2O (r = −0.976, P < 0.01 and r = −0.781, P < 0.05, respectively). Denitrification rate and the percentage of total gases present as N2O increased as the nitrate (NO3 −) concentration increased. However, there was no effect of NO3 − concentration on the percentage of total N gases present as NO. Our results indicate that the potential N loss through denitrification may be higher in alkaline paddies than that in neutral and acidic paddies. Moreover, the variation of the N2O percentage in denitrification products of different paddy soils should be considered when estimating the denitrification-derived N2O emission and when calculating the N budget in paddy soils.

Spatial Distribution of Ions in Groundwater under Agricultural Land

This study investigated the characteristics of shallow groundwater quality under agricultural areas dominated by rice paddy fields, vegetable fields, and a residential zone on an alluvial basin by examining spatial distributions of Cl\u., Na\u+, NO\u-\d3, and SO²\d4\u- concentrations. Seasonal changes in spatial distribution of ion concentrations during one cultivation period and the causes of the changes were discussed. Changes in spatial distribution of Cl. and Na+ concentrations of the groundwater were mainly affected by seasonal changes in precipitation concentrations. NO\u-\d3 concentration was strongly influenced by fertilization of vegetable fields and a following heavy rainfall. Elevated NO\u-\d3 concentration was less likely to occur under paddy fields than under vegetable fields. It was suggested that paddy fields might mitigate NO\u-\d3 contamination of shallow groundwater possibly because of denitrification in paddy soil in an anaerobic state during ponding. As for SO²\d4\u-, it was acknowledged that there could be a specific point source near a particular observation well.

The Action of Pesticides on the Denitrification in Paddy Soil (Part 2)

The Action of Pesticides on the Denitrification in Paddy Soil (Part 2)