Effect of nitrogen fertilization on the fate of rice residue-C in paddy soil depending on depth: 13C amino sugar analysis
A 100-day incubation experiment was conducted to (i) trace the fate of rice residue-derived 13C in the amino sugar (AS) pool in 0–1-cm (oxic) and 1–5-cm (anoxic) layers of paddy soil and (ii) evaluate the effects of inorganic N ((NH4)2SO4) fertilization on the formation of AS at early and late incubation times (5 and 100 days, respectively). The accumulation of rice residue-derived AS occurred at 5 and 100 days in both soil layers as a result of AS stabilization. Inorganic N addition increased the contents of rice residue-derived muramic acid, glucosamine, and galactosamine in the 0–1-cm soil layer for both incubation times by average on 14.7–20.8%, 23.7–31.8%, and 11.6–23.3%, respectively. In contrast, no effects of N fertilization on AS content in the 1–5-cm soil layer were found. The amount of rice residue-derived AS was higher in the 1–5-cm than in the 0–1-cm soil layer at early incubation time, probably due to the higher contents of ammonium here compared to the upmost oxic layer where nitrate was the dominated N form. Thus, the preferential uptake of ammonium but not nitrate by microorganisms led to the higher formation of rice residue-derived AS in the anoxic soil layer. The ratio of fungal to bacterial residues (fungal glucosamine/muramic acid) ranged between 1.0 and 1.7 for rice residue-derived AS and was 12.5–14.6 for total AS, indicating that fungi and bacteria have similar contributions to the decomposition of fresh rice residue whereas native soil organic matter (SOM) is a fungi-predominated process. This study emphasized that coupling of C and N cycles in paddy soils is different in oxic and anoxic layers, resulting in variation of plant residue decomposition and formation of SOM.
KeywordsMicrobial biomarkers Amino sugar 13C compound-specific isotope labeling Inorganic N fertilization Soil depth Paddy soil
This study was supported by the National key Research Program (2016YFD0200106, 2017YFC0505503), National Natural Science Foundation of China (41671298, 41430860), and Youth Innovation Team Project of ISA, CAS (2017QNCXTD_GTD).
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