Climate and Vegetation-Driven Increase of Soil Heterotrophic and Autotrophic Respiration in China's Subtropical Forests Over 2000–2020

Soil respiration significantly counteracts the carbon sequestration of forest ecosystems, but large uncertainties remain in quantifying its components including heterotrophic (HR) and autotrophic respiration (AR). We used previously collected field data from subtropical forests of southern China, and developed independent models for HR and AR. The HR model incorporated the regulation of substrate quantity and quality and co-limitations of soil temperature and moisture on microbe activity. The AR model considered fine root biomass and productivity as substrates and temperature effects on root activity. Using high-quality forcing data and new models, we estimated HR and AR in this region over 2000–2020 with 8-day timescale and 1 km spatial resolution. Validation with independent data showed improved accuracy compared with previous estimates. We estimated annual HR at 523 ± 381 g C m⁻² yr⁻¹ and AR at 254 ± 112 g C m⁻² yr⁻¹ (values represent mean ± SD). While previous HR estimates align well with our results, previous AR estimates are generally higher. Our estimates exhibited more detailed spatial patterns than existing data sets, particularly along altitudinal gradients, and showed significant increasing trends in both HR and AR driven by warming and greening, especially in high-rate region and during summer season. Soil temperature was the main driver for the interannual variation of HR especially in cold environments, while leaf area index mainly contributed to that of AR in most regions. Our results provide critical constraints on the estimates of HR and AR in subtropical forests and enhance our understanding of their contributions and spatiotemporal patterns under a changing climate.