Temperature-Dependent Soil Organic Carbon Turnover in Taiwan’s Forests Revealed by Stable Carbon Isotope Analysis

High-standing islands, such as Taiwan, offer unique opportunities to study soil organic carbon (SOC) dynamics due to their steep terrains, rapid erosion, and strong climatic gradients. In this study, we investigated 54 forest soil profiles across northern, central, and southern Taiwan to assess SOC inventories and turnover using stable carbon isotope (δ¹³C) analyses. We applied Rayleigh fractionation modeling to vertical δ¹³C enrichment patterns and derived the parameter β, which serves as a proxy for SOC turnover rates. Our findings reveal that SOC stocks increase notably with elevation, aligning with lower temperatures and reduced decomposition rates at higher altitudes. Conversely, mean annual precipitation (MAP) did not show a straightforward relationship with SOC stocks or β, highlighting the moderating effects of soil drainage, topography, and local hydrological conditions. Intriguingly, higher soil nitrogen levels were associated with a negative correlation to ln(β), underscoring the complex interplay between nutrient availability and SOC decomposition. Overall, temperature emerges as the dominant factor governing SOC turnover, indicating that ongoing and future warming could accelerate SOC losses, especially in cooler, high-elevation zones currently acting as stable carbon reservoirs. These insights underscore the need for models and management practices that account for intricate temperature, moisture, and nutrient controls on SOC stability, as well as the value of stable isotopic tools for evaluating soil carbon dynamics in mountainous environments.