Paddy fields are a common type of agricultural land in China and usually have higher soil organic carbon and microbial residue carbon content than adjacent drylands. However, the microbial metabolism of soil organic carbon in paddy fields and drylands is not well characterized. Therefore, analyzing the response of soil microbial carbon metabolism to land use practices is crucial for designing appropriate farmland management practices to improve soil carbon sequestration capacity.
A team of researchers from the Center for Watershed Agro-Environmental Research, Institute of Subtropical Agroecology, Chinese Academy of Sciences (CAS), Wu Jinshui, randomly collected 240 pairs of paddy field and dryland surface soils in four rice-distributed climatic zones in eastern China (mesothermal-black soil, warm-temperate tidal soil, subtropical-red soil, and tropical-brick-red soil) by using the principle of paired sampling. The research team randomly selected 10 pairs of paddy and dryland soils in each climatic zone to add 18O-H2O for short-term incubation to determine the microbial uptake, growth, respiration, and utilization efficiencies of soil total organic carbon. The results showed that microbial growth efficiency was lower and respiration efficiency was higher in dryland soils from warm climate zones (subtropical and tropical) compared to dryland soils from cold climate zones (mesothermal and warm temperate). This was attributed to the shift in microbial carbon metabolism from growth to respiration due to the low pH and high clay content of the soils in the warm climatic zone. However, microbial growth and respiration efficiencies were significantly lower in paddy soils in the warm climatic zone than in paddy fields in the cold climatic zone, probably due to the inhibition of microbial carbon metabolism in response to low soil pH by prolonged flooding. The lower microbial carbon uptake efficiency in paddy fields compared to dryland soils under the four climatic zones suggests lower microbial involvement in the process of organic carbon accumulation in paddy soils; the higher growth and lower respiration efficiencies of microorganisms in paddy soils compared to dryland soils resulted in higher microbial carbon utilization efficiency in paddy soils. The difference in microbial carbon utilization efficiency between paddy and dryland soils showed a significant positive correlation with the difference in soil organic carbon and microbial residual carbon. In terms of microbial carbon metabolism, paddy fields had higher organic carbon content than dryland soils due to weaker microbial carbon uptake and stronger anabolism in paddy soils. Therefore, farm management practices that strengthen microbial anabolism and reduce microbial catabolism are important tools to increase soil carbon sequestration.
The results of this study were published in Soil and Tillage Research under the title Higher microbial C use efficiency in paddy than in adjacent upland soils: evidence from continental scale. Soil and Tillage Research. The research was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China.
Microbial carbon uptake, growth, respiration and carbon utilization efficiency in paddy and dryland soils in four climatic zones in eastern China
