Fungal and bacterial N2O production regulated by soil amendments of simple and complex substrates |
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| Affiliation: | 1. Helmholtz Zentrum München, Research Unit Environmental Genomics, Department of Environmental Sciences, Ingolstädter Landstraße 1, 85764 Oberscheleißheim, Germany;2. Technische Universität Berlin, Chair Waste Management and Environmental Research, Department of Ecology, Ernst Reuter Platz 1, 10587 Berlin, Germany;3. Helmholtz Zentrum München, Research Unit Environmental Simulation, Department of Environmental Sciences, Ingolstädter Landstraße 1, 85764 Oberscheleißheim, Germany;4. University of Bonn, Institute of Crop Science and Resource Conservation, Division Soil Science, Nussallee 13, D-53115 Bonn, Germany;1. Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan;2. Niigata Agricultural Research Institute, Niigata 940-0826, Japan;3. Department of Bioresource Science, College of Agriculture, Ibaraki University, Ibaraki 300-0393, Japan;4. Department of Forest Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan;1. Department of Soil Science, North Carolina State University, Raleigh, NC, 27695, USA;2. Environmental Sciences Division, National Exposure Research Laboratory, U.S. Environmental Protection Agency, RTP, NC, USA;3. Air Pollution Prevention and Control Division, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, RTP, NC, USA;1. Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, People’s Republic of China;2. Key Laboratory of Urban Environmental Processes and Pollution Control, Ningbo Urban Environment Observation and Research Station-NUEORS, Chinese Academy of Sciences, Ningbo, 315800, People’s Republic of China;3. University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China;4. Research Center for Environmental Ecology and Engineering, School of Environmental Ecology and Biological Engineering, Wuhan Institute of Technology, 206 Guanggu 1st Road, Wuhan, 430205, People’s Republic of China;5. The James Hutton Institute, Aberdeen, AB15 8QH, UK |
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| Abstract: | Fungal N2O production results from a respiratory denitrification that reduces NO3−/NO2− in response to the oxidation of an electron donor, often organic C. Despite similar heterotrophic nature, fungal denitrifiers may differ from bacterial ones in exploiting diverse resources. We hypothesized that complex C compounds and substances could favor the growth of fungi over bacteria, and thereby leading to fungal dominance for soil N2O emissions. Effects of substrate quality on fungal and bacterial N2O production were, therefore, examined in a 44-d incubation after soils were amended with four different substrates, i.e., glucose, cellulose, winter pea, and switchgrass at 2 mg C g−1 soil. During periodic measurements of soil N2O fluxes at 80% soil water-filled pore space and with the supply of KNO3, substrate treatments were further subjected to four antibiotic treatments, i.e., no antibiotics or soil addition of streptomycin, cycloheximide or both so that fungal and bacterial N2O production could be separated. Up to d 8 when antibiotic inhibition on substrate-induced microbial activity and/or growth was still detectable, bacterial N2O production was generally greater in glucose- than in cellulose-amended soils and also in winter pea- than in switchgrass-amended soils. In contrast, fungal N2O production was more enhanced in soils amended with cellulose than with glucose. Therefore, fungal-to-bacterial contribution ratios were greater in complex than in simple C substrates. These ratios were positively correlated with fungal-to-bacterial activity ratios, i.e., CO2 production ratios, suggesting that substrate-associated fungal or bacterial preferential activity and/or growth might be the cause. Considering substrate depletion over time and thereby becoming limited for microbial N2O production, measurements of soil N2O fluxes were also carried out with additional supply of glucose, irrespective of different substrate treatments. This measurement condition might lead to potentially high rates of fungal and bacterial N2O production. As expected, bacterial N2O production was greater with added glucose than with added cellulose on d 4 and d 8. However, this pattern was broken on d 28, with bacterial N2O production lower with added glucose than with added cellulose. In contrast, plant residue impacts on soil N2O fluxes were consistent over 44-d, with greater bacterial contribution, lower fungal contribution, and thus lower fungal-to-bacterial contribution ratios in winter pea- than in switchgrass-amended soils. Real-time PCR analysis also demonstrated that the ratios of 16S rDNA to ITS and the copy numbers of bacterial denitrifying genes were greater in winter pea- than in switchgrass-amended soils. Despite some inconsistency found on the impacts of cellulose versus glucose on fungal and bacterial leading roles for N2O production, the results generally supported the working hypothesis that complex substrates promoted fungal dominance for soil N2O emissions. |
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| Keywords: | Fungi Bacteria Nitrous oxide Glucose Cellulose Plant residues |
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