Low soil C:N ratio results in accumulation and leaching of nitrite and nitrate in agricultural soils under heavy rainfall |
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| Authors: | Xiaosong YANG Zhengyi HU Zijian XIE Songyan LI Xiaolei SUN Xianlin KE and Mingming TAO |
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| Institution: | 1 Resource and Environmental College, University of Chinese Academy of Sciences, Beijing 100049(China)
2 Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100049(China)
3 National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Sciences, Beijing 100012(China)
4 Institute of Bio-and Geosciences, Agrosphere(IBG-3), Forschungszentrum Jülich, Jülich 52425(Germany) |
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| Abstract: | Nitrate (NO3-) and nitrite (NO2-) leaching threatens groundwater quality. Soil C:N ratio, i.e., the ratio of soil organic carbon to total nitrogen, affects mineralization, nitrification, and denitrification; however, its mechanism for driving soil NO3-and NO2-accumulation and leaching remains unclear. Here, a field investigation in a fluvo-aquic soil and a soil column experiment were performed to explore the relationships between soil C:N ratio and soil NO3-and NO2-leaching in three soil layers (0-20, 20-40, and 40-60 cm) under heavy rainfall (rainfall rate > 25 mm d-1). The field investigation results showed that both soil NO3--N and NO2--N contents decreased exponentially (P < 0.001) with increasing soil C:N ratio in each soil layer. Furthermore, negative exponential relationships (P < 0.001) were found between soil C:N ratio and both NO3--N and NO2--N concentrations in soil solution in each soil layer under heavy rainfall. The soil column divided into three layers was leached with simulated heavy rainfall; the results confirmed negative exponential relationships (P < 0.05) between soil C:N ratio and both NO3--N and NO2--N concentrations in the leachate from each soil layer. A total of 18 soil samples obtained from three depths at six field sites during the rainy season were used to elucidate the microbial mechanisms induced by soil C:N ratio using high-throughput sequencing and real-time polymerase chain reaction. High abundances of ammonifying bacteria (Flavobacterium, Bacillu, and Pseudomonas), ammonia-oxidizing bacteria (Nitrosospira), and nirS/K gene were observed when soil C:N was low, concomitant with low abundances of NO2--oxidizing bacteria (Nitrospira) and narG gene. Partial least squares path modeling showed that the high NO3-and NO2-levels at low soil C:N ratio might be attributed to the inhibition of NO3-reduction (i.e., low narG gene) and NO2-oxidation (i.e., low Nitrospira) and thus the accumulation of soil NO3-and NO2-, respectively. Therefore, the leaching of NO2-and NO3-in low C:N soils requires more attention during the rainy season. |
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| Keywords: | ammonia-oxidizing bacteria ammonifying bacteria functional gene microbial community nitrite-oxidizing bacteria |
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