Temperature fluctuation affects soil organic carbon accumulation through soil enzyme activity and nutrient limitation

Soil is the larger carbon (C) sink in the terrestrial ecosystem. However, in the context of climate change, which can cause extreme weather events and temperature fluctuations, it is unclear how such fluctuations affect the formation, retention, and loss of soil organic carbon (SOC). This study investigated the relationships between soil enzyme activities, priming effect, nutrient limitation, and SOC accumulation under three degrees of temperature fluctuation amplitudes (25 °C, 25 °C ± 10 °C and 25 °C ± 20 °C) and three moisture conditions. The results showed that under small-amplitude temperature fluctuations, β-glucosidase and N-acetyl-β-glucosaminidase activities increased by 6.88 % and 12.38 %, respectively, and microbial carbon limitation decreased (vector length reduced by 0.09). In contrast, under large-amplitude temperature fluctuations, soil enzyme activities declined significantly, causing microbes to allocate more carbon to maintenance respiration, and after 28 days of soil incubation, SOC decreased by 0.57 g kg⁻¹ on average. The results of structural equation modeling showed that small-amplitude temperature fluctuations promoted soil enzyme activities, increased the soil organic matter priming effect, and lowered soil microbial nutrient limitation, contributing to SOC accumulation. Larger-amplitude temperature fluctuations above a certain range affect enzyme activity and inhibited microbial activity compared to a constant temperature state, resulting in microorganisms using more energy to maintain metabolism, and thus less C allocation for their formation, and less accumulation of their own SOC. These findings offer new insights into how SOC dynamics respond to temperature fluctuations and lay a foundation for future research aimed at refining the understanding of soil feedback mechanisms in climate change. • Temperature fluctuations affected soil enzyme activity, priming effect, and nutrient limitation. • Small-temperature fluctuations enhanced soil enzyme activity and PE, reduced nutrient limitation and increased SOC. • Larger-temperature fluctuations reduced SOC by inhibiting soil enzyme activity and intensifying nutrient limitation. • Temperature fluctuations beyond thresholds lead microbes to expend more energy on metabolic maintenance, reducing SOC.