Nitrogen fertilization increases rhizodeposit incorporation into microbial biomass and reduces soil organic matter losses |
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| Authors: | Email author" target="_blank">Huadong?ZangEmail author Evgenia?Blagodatskaya Jinyang?Wang Xingliang?Xu Yakov?Kuzyakov |
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| Institution: | 1.Department of Agricultural Soil Science,University of G?ttingen,G?ttingen,Germany;2.Department of Soil Science and Temperate Ecosystems,University of G?ttingen,G?ttingen,Germany;3.Institute of Physicochemical and Biological Problems in Soil Science,Russian Academy of Sciences,Pushchino,Russia;4.State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science,Chinese Academy of Sciences,Nanjing,China;5.Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources,Chinese Academy of Sciences,Beijing,China |
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| Abstract: | Agricultural soils receive large amounts of anthropogenic nitrogen (N), which directly and indirectly affect soil organic matter (SOM) stocks and CO2 fluxes. However, our current understanding of mechanisms on how N fertilization affects SOM pools of various ages and turnover remains poor. The δ13C values of SOM after wheat (C3)-maize (C4) vegetation change were used to calculate the contribution of C4-derived rhizodeposited C (rhizo-C) and C3-derived SOM pools, i.e., rhizo-C and SOM. Soil (Ap from Haplic Luvisol) sampled from maize rhizosphere was incubated over 56 days with increasing N fertilization (four levels up to 300 kg N ha?1), and CO2 efflux and its δ13C were measured. Nitrogen fertilization decreased CO2 efflux by 27–42% as compared to unfertilized soil. This CO2 decrease was mainly caused by the retardation of SOM (C3) mineralization. Microbial availability of rhizo-C (released by maize roots within 4 weeks) was about 10 times higher than that of SOM (older than 4 weeks). Microbial biomass and dissolved organic C remained at the same level with increasing N. However, N fertilization increased the relative contribution of rhizo-C to microbial biomass by two to five times and to CO2 for about two times. This increased contribution of rhizo-C reflects strongly accelerated microbial biomass turnover by N addition. The decomposition rate of rhizo-C was 3.7 times faster than that of SOM, and it increased additionally by 6.5 times under 300 kg N ha?1 N fertilization. This is the first report estimating the turnover and incorporation of very recent rhizo-C (4 weeks old) into soil C pools and shows that the turnover of rhizo-C was much faster than that of SOM. We conclude that the contribution of rhizo-C to CO2 and to microbial biomass is highly dependent on N fertilization. Despite acceleration of rhizo-C turnover, the increased N fertilization facilitates C sequestration by decreasing SOM decomposition. |
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