Rice fields have higher efficiency in the use of microbial carbon sources than dryland soils

Paddy is the most common type of farmland in China, which usually has higher soil organic carbon and microbial residual carbon content than adjacent dry land. However, the microbial metabolic profile of soil organic carbon in paddy and dryland is unclear. Interpreting the response of soil microbial carbon metabolism to land use patterns is essential for designing appropriate farmland management practices to improve soil carbon sequestration.

Rice fields after harvest. Photo by Chen Xiangbi

Wu Jinshui’s team, a researcher at the Research Center for Watershed Agro-Environment of the Institute of Subtropical Agroecology, Chinese Academy of Sciences, randomly collected 240 pairs of paddy and dryland topsoil in four rice distribution climate zones in eastern China (middle temperate-black soil, warm temperate-tidal soil, subtropical-red soil and tropical-brick red soil). Among them, 10 pairs of paddy and dryland soils were randomly selected for short-term cultivation with oxygen 18 water in each climate zone, and the microbial uptake, growth, respiration and utilization efficiency of total soil organic carbon were determined.

The results showed that the soil in the dry land in the warm climate zone (subtropical and tropical) had lower microbial growth efficiency and higher respiration efficiency than the dry land in the cold climate zone (middle temperate and warm temperate zone), mainly due to the low pH and high clay content of the soil in the warm climate zone, which led to the transition of microbial carbon metabolism from growth to respiration. However, the growth and respiration efficiency of soil microorganisms in paddy fields in warm climate regions were significantly lower than those in paddy fields in cold climate regions, which may be due to long-term flooding inhibiting the response of microbial carbon metabolism to low soil pH.

Dry land. Photo by Chen Xiangbi

Under the four climate zones, the efficiency of soil microbial carbon uptake in dryland was low, indicating that the participation of microorganisms in the accumulation of soil organic carbon in paddy fields was low. Compared with dryland soil, the growth efficiency of soil microorganisms in paddy fields is higher and the respiration efficiency is lower, which makes the soil microbial carbon use efficiency higher. The differences in soil microbial carbon use efficiency in paddy and dryland were significantly positively correlated with the differences in soil organic carbon and microbial residual carbon. From the perspective of microbial carbon metabolism, the drier soils of paddy fields have higher organic carbon content due to their weaker microbial carbon uptake and stronger anabolism.

Based on the above results, the research team believes that farmland management measures to strengthen microbial anabolism and reduce microbial catabolism are important means to increase soil carbon sequestration.

The results were published online Sept. 20 in Soil and Tillage Research. The research was jointly funded by the National Key R&D Program of the 14th Five-Year Plan and the National Natural Science Foundation of China. (Source: China Science News, Wang Haohao, Duan Xun)

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