2026/02/03 by Noppol Arunrat, Sukanya Sereenonchai, Hajime SAKURADA +3 · 1 voice
Agricultural and Biological Sciences · Environmental Science · #Ecology and Vegetation Dynamics Studies #Fire effects on ecosystems #Soil Carbon and Nitrogen Dynamics
paper · doi:10.1007/s10533-026-01305-3
openalex publication_date 2026/02/03 · openalex created_date 2026/02/04 · openalex updated_date 2026/07/29
Understanding the biogeochemical consequences of fire and land-use history in tropical upland systems is essential for sustainable soil management. We investigated the vertical distribution of stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes in soils under rotational shifting cultivation (RSC) in Northern Thailand. Three fields with distinct land-use histories were analyzed: a continuously fallow site for seven years (CF-7Y), a six-year fallow RSC site (RSC-6Y), and a twelve-year fallow RSC site (RSC-12Y). The RSC-6Y and RSC-12Y fields were left fallow for 6 and 12 years, respectively, with both fields burned in 2022 and entered a new two-year fallow phase. By contrast, CF-7Y field was last burned in 2017 and has remained under continuous fallow since that time. In 2024, soil samples were collected from upper, middle, and lower slope positions to analyze total organic carbon (TOC), total nitrogen (TN), TOC:TN, and δ 13 C and δ 15 N signatures across the 0–100 cm soil profile. Results revealed that longer fallow periods (RSC-12Y) enhanced vertical movement and stabilization of TOC and TN, with more enriched δ 13 C and δ 15 N values at depth—indicative of legacy fire effects and microbial transformation. The CF-7Y field showed high surface TOC and more negative δ 13 C values, reflecting active C₃ vegetation inputs and minimal decomposition. The δ 13 C values were significantly affected by both site and slope position, suggesting independent influences of land-use history and topography on soil carbon dynamics. In contrast, δ 15 N was shaped by a significant interaction between site and slope, indicating that nitrogen cycling processes vary with the combined effects of land use and topographic gradient. The δ 15 N values consistently increased with depth across all fields, particularly in lower slope positions, suggesting deposition of 15 N-enriched material and persistent alteration of nitrogen pools post-fire. Slope position significantly influenced nutrient distribution, with lower slopes acting as nutrient sinks and upper slopes experiencing erosion-driven losses. These findings underscore the decoupled recovery of soil carbon and nitrogen cycles after disturbance, highlighting the need for slope-sensitive and nutrient-aware restoration strategies.