Microbial-mediated decline in mineral-associated organic carbon following rice terrace abandonment in subtropical China

Description

Rice terraces (RT) play a crucial role in sustaining soil carbon sequestration and ecosystem services, yet face increasing abandonment. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) differ markedly in their formation and stability. A carbon fraction perspective helps reveal the impacts of terrace abandonment on soil organic carbon (SOC) and its microbial mechanisms, which remain poorly understood. This study investigated six typical RT and their paired abandoned terraces (mainly converted to upland or forest) in subtropical China. It evaluated the effects of RT abandonment on SOC and its underlying drivers. The results showed that RT abandonment significantly reduced SOC content and shifted its composition, primarily due to declines in MAOC, while POC remained unchanged. MAOC decline was primarily driven by reductions in microbial necromass carbon, particularly that derived from fungi. Moreover, in the 0-20 cm soil layer, variations in MAOC were primarily regulated by intensified microbial carbon limitation, along with declines in microbial biomass and carbon use efficiency. In the 40-60 cm soil layer, changes in MAOC were more strongly influenced by enhanced microbial co-limitation by carbon and phosphorus and an increased dominance of K-strategist microbial communities. These findings suggest that RT function as stabilizers of SOC, whereas abandonment weakens their capacity to maintain soil carbon stability. In particular, changes in MAOC are strongly regulated by microbial nutrient limitation and life-history strategies. Therefore, preventing terrace abandonment and implementing sustainable management strategies are critical for sustaining soil carbon stability.

Steps to reproduce

The subtropical region of China hosts the world’s highest concentration of RT, most of which have been cultivated for several centuries. In this study, six representative RT sites were selected across the subtropical region of China, including the Hani terraces in Yunnan Province, Jiabang terraces in Guizhou Province, Longji terraces in Guangxi Province, Ziquejie terraces in Hunan Province, Shangbao terraces in Jiangxi Province, and Lianhe terraces in Fujian Province. These sites span a distance of over 2000 km (23°07′-27°41′ N, 102°49′-118°11′ E). The mean annual temperature across the study sites ranged from 14.81 to 17.45 °C, while mean annual precipitation varied from 1597.75 to 2134.84 mm, all falling within the subtropical monsoon climate zone. Soil samples were collected from two depth intervals (0-20 cm and 40-60 cm). Prior to soil sampling, surface litter as well as visible plant and animal residues were carefully removed. Soil samples were collected from the 0-20 cm and 40-60 cm soil layers at each site. For each land-use type, three standard plots were established, and three random sampling points were selected within each plot. Soils collected from the same depth within each plot were thoroughly homogenized to form one composite sample, resulting in a total of 108 samples. All samples were kept cool using ice packs during transport to the laboratory. Upon arrival, soils were passed through a 2 mm sieve to remove roots, stones, and other debris. Each composite sample was then subdivided into three subsamples for subsequent analyses.

Institutions

• Jiangxi Agricultural University

  Jiangxi, Nanchang
• Hunan Normal University

  Hunan, Changsha

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