Greater promotion of DNRA rates and nrfA gene transcriptional activity by straw incorporation in alkaline than in acidic paddy soils

Abstract

Dissimilarity nitrate reduction to ammonium (DNRA) is of significance in agriculture ecosystems as the process is beneficial to N retention in soils. However, how fertilization regimes influence DNRA rates and functional microbes in agriculture was rarely estimated. In the present study, a 2-year pot experiment was conducted in two contrasting paddy soils to evaluate the effects of straw and nitrogen addition on DNRA process and the related functional microbes, using stable isotope tracer and molecular ecology techniques. The results showed that the abundance and transcription activity of nitrite reductase encoding gene (nrfA) involved in DNRA process and DNRA rates were significantly higher in alkaline soils than in acidic soils. Straw incorporation significantly enhanced nrfA gene abundance and transcription activity, with a greater effect in alkaline soil than in acidic soil. The rates of DNRA, abundance and transcription activity of nrfA gene positively correlated to soil C/N and C/NO 3 induced by straw application. Sequencing analysis based on nrfA gene transcript showed that Deltaproteobacteria was the most dominant group in both soil types (30.9%-67.4%), while Gammaproteobacteria, Chloroflexi, Actinobacteria were selectively enriched by straw incorporation. These results demonstrated that DNRA activity can be improved by straw return practice in paddy soils while the effect will vary among soil types due to differentiated functional microbial communities and edaphic properties.

Global Patterns and Drivers of Soil Dissimilatory Nitrate Reduction to Ammonium

“…Soil pH is the second most important factor controlling DNRA as it is stimulated at higher soil pH. This result is consistent with previous results of Corrêa and Germon, Stevens et al, and Bai et al., who found that higher DNRA is often recorded in alkaline environments. Similarly, Zhang et al recorded 98% conversion of NO 3 – to NH 4 + by the DNRA in alkaline soil.…”

“…Soil pH regulates DNRA through its effect on the abundances of nrfA, nitrite reductase-encoding gene related to DNRA, which reaches its optimum activity at pH > 7.5 . Higher DNRA rates are linked with higher nrfA gene levels. ,,− Recently, Bai et al found that DNRA rates and the transcription activity and abundance of nrfA were significantly lower in acidic soils than that in alkaline soils. Moreover, soil microbial activity enhanced with raising soil pH from 3.0 to 7.7, − thus stimulating DNRA.…”

“…Carbon provides electrons through fermentation or respiration, which reduces NO 3 – to NH 4 + and thus supplies energy to DNRA bacteria. , Several studies stated that DNRA is stimulated under the application of organic C compounds. − Furthermore, some studies argued that the electron donor-to-acceptor ratio (i.e. C/NO 3 – ) is a key controller in the partitioning of NO 3 – reduction between DNRA and denitrification. ,, In soils incubated under different oxygen levels with the same contents of NO 3 – combined with various rates of C additions, Fazzolari et al found that the influence of oxygen on DNRA was dependent on C/NO 3 – and reported that C rather than oxygen was the master factor controlling NO 3 – partitioning between DNRA and denitrification. Other recent studies demonstrated the importance of C/NO 3 – on partitioning NO 3 – reduction between denitrification and DNRA, ,, which supports the view of Tiedje .…”

“…Other recent studies demonstrated the importance of C/NO 3 – on partitioning NO 3 – reduction between denitrification and DNRA, ,, which supports the view of Tiedje . Recently, Bai et al found that DNRA rates and the transcription activity and abundance of nrfA gene increased significantly with increasing soil C/NO 3 – induced by straw addition. Moreover, Minick et al found that DNRA was lower at low redox potential compared to high redox potential and negatively associated with C/NO 3 – , manifesting that NO 3 – pool size is the key factor controlling soil DNRA.…”

“…Another important finding in our study is that global precipitation is the main stimulator for DNRA. Many previous studies argued that C/NO 3 − rather than precipitation drives DNRA, 8,35 and that DNRA is a source of N 2 O emissions. 36 However, our study revealed no firm relationship between DNRA and C/NO 3 − at the global scale, whereas N 2 O emissions decreased significantly with increasing DNRA rates highlighting the ecological importance of DNRA as the potential mechanism to reducing N losses (e.g., N 2 O emissions).…”