Paddy soils make up the largest anthropogenic wetlands on the Earth. They are characterized by a prominent potential for organic carbon (C) sequestration.

Recently, a research group led by Prof. SU Yirong from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences elucidated the soil organic carbon (SOC) sequestration pathways in paddy and upland, which provided a strong scientific basis for the management of SOC pools in the agricultural lands.

This study was published in Global Change Biology on Mar. 14.

Based on the paired sampling principle, the researchers collected 240 paired paddy and upland soil samples from the four main grain-producing areas in mid temperate, warm temperate, subtropics, and tropics across eastern China.

They found that paddies were 39%-127% more efficient in SOC sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates.

A further 40 pairs of soil samples were randomly selected to quantify the contribution of plant- and microbial-derived C to SOC accumulation based on biomarkers analysis of lignin and amino sugar, respectively.

Results showed that 33%-54% of the SOC accumulated in paddy soils derived from plant residues, whereas they only contributed 19%-42% in uplands. Concurrently, 28%-36% of SOC stored in paddies was microbial-derived compared to 40%-59% in uplands. Approximately 3.3 times larger stocks of lignin phenols were observed in paddy relative to upland.

The research indicated that great SOC sequestration efficiency in paddy was mainly attributed to the limitation of microbial activity and inhibition of the decomposition process of plant residues caused by flooding, which promoted the direct accumulation of plant residues.

In the scenario of converting all paddies to uplands across eastern China, 504 Tg of C will be lost from the topsoil (0-15 cm) of paddy, which is equivalent to 13% of organic C stocks in surface soils of all Chinese croplands. Approximate 98% of total C loss occurs in warmer climates of the subtropics and tropics.

"These findings highlight the importance of preserving paddy systems and other anthropogenic wetlands in subtropical and tropical areas, and emphasize that proper water management is the pivotal to reducing C loss from paddy soils," said Prof. SU Yirong.  

Contact: CHEN Xiangbi

E-mail: xbchen@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences

FIGURE 1 Contents of soil organic C .The horizontal dashed lines show the average values (across four climates) for paddy (blue) and upland (orange) soils. (Image by ISA)

FIGURE 2 Contributions of plant- and microbial-derived C in total SOC in paddy and upland soils across the four climate zones. (Image by ISA)

FIGURE 3 Diagram illustrating the formation of SOC in water-logged paddy and well drained upland. Black and red arrows represent the pathways of plant- and microbial derived C, respectively. The size of the arrows reflects the intensity of the pathways. (Image by ISA)