# Seasonal and interannual variations of soil heterotrophic respiration and autotrophic respiration in subtropical forests of southeast China: independent process-based models

## TL;DR

This study develops separate models to track soil respiration components in subtropical forests, revealing how each responds differently to seasonal and climate changes.

## Contribution

The paper introduces independent process-based models for heterotrophic and autotrophic respiration in subtropical forests.

## Key findings

- Heterotrophic respiration rates were higher than autotrophic respiration annually.
- Autotrophic respiration showed a significant increasing trend over 2002–2022.
- Both respiration components exhibited strong seasonal and interannual variability.

## Abstract

Soil respiration consists of two distinctive components: heterotrophic respiration (decomposition of soil organic matter) and autotrophic respiration (CO2 production from root system), which are driven by different factors. However, the absence of process-based independent models for the two components hampers our ability to accurately quantify and understand the key carbon sources on land. Here, we used observational data to develop independent models for both soil heterotrophic and autotrophic respiration in the subtropical forests of southeast China, and validated the models using independent field data. Applying the validated models, we estimated both soil heterotrophic respiration and autotrophic respiration at three forest sites over 2002–2022. Our results showed higher annual rates of heterotrophic respiration (0.8–1.6 g C m−2 day−1) than autotrophic respiration (0.5–0.8 g C m−2 day−1). There was significant seasonality and inter-annual variability in both components, with larger variations in autotrophic respiration. The inter-annual variation was strongest in the winter season for both two respiration components. We found a significant (p < 0.01) increasing trend in autotrophic respiration (with a slope of 2.0–6.0 g C m−2 year−2) but not in heterotrophic respiration over 2002–2022. There was also a significant increasing trend in total soil respiration (3.4–6.2 g C m−2 year−2 for slopes), indicating an increasing role of autotrophic respiration. Our results reveal the dynamic nature of soil heterotrophic respiration and autotrophic respiration and their differing responses to environmental changes, emphasizing the need for independent models to improve the understanding of soil CO2 sources in a changing climate.

The online version contains supplementary material available at 10.1186/s40562-025-00399-1.