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. Plain Language Summary: Soil respiration, the process through which soil releases carbon dioxide (CO2) into the atmosphere, counteracts the carbon sequestration ability of forest ecosystems. Soil respiration consists of heterotrophic respiration (HR) (decomposition of soil organic matter) and autotrophic respiration (AR) (root respiration). In this study, we collected field data from China's subtropical forests and developed independent models to estimate the rates of heterotrophic and autotrophic respiration over 2000–2020 in this region. Validation showed that our estimates not only improved spatial and temporal resolution compared to existing data sets, but also exhibited high accuracy. Comparative analysis revealed that while previous estimates for HR are close to our results, those for AR were generally higher. Our estimates revealed significantly increasing trends in both respiration rates, suggesting increasing CO2 emission from soils in subtropical forest of China. Further analysis showed ST and LAI (an indicator reflecting forest biomass) were the main driving factors for the interannual variations of HR and AR, respectively. These findings provide new insights for understanding soil respiration dynamics in subtropical forests and their responses to climate change. Key Points: Independent models were applied to estimate soil heterotrophic (HR) and autotrophic respiration (AR) in China's subtropical forestsNew estimates revealed significant increasing trends in both HR and AR from 2000 to 2020HR interannual variation was primarily linked to soil temperature, and AR interannual variation was more closely link to leaf area index [ABSTRACT FROM AUTHOR]