Rice biomass production and carbon cycling in 13CO2 pulse-labeled microcosms with different soils under submerged conditions

Rice fields are an important source for the greenhouse gas methane. Plants play an essential role in carbon supply for soil microbiota, but the influence of the microbial community on carbon cycling is not well understood. Microcosms were prepared using sand-vermiculite amended with different soils and sediments, and planted with rice. The microcosms at different growth stages were pulse-labeled with (CO2)-C-13 followed by tracing C-13 in plant, soil and atmospheric carbon pools and quantifying the abundance of methanogenic archaea in rhizosphere soil. Overall, > 85 % of the freshly assimilated carbon was allocated in aboveground plant biomass, approximately 10 % was translocated into the roots and < 2 % was recovered in soil organic matter, independently from soil type. Only about 0.3 % was transformed to CH4, but emission of C-13-labeled CH4 started immediately and C-13 enrichment revealed that plant-derived carbon was an important source for methanogenesis. The results further demonstrated that carbon assimilation and translocation processes, microbial abundance and gas emission were not only affected by the plant growth stage, but also by the content and type of soil in which the rice plants grew. The study illustrates the close ties between plant physiology, soil properties and microbial communities for carbon turnover and ecosystem functioning.