The differences of seasonal and inter-annual variations  between soil heterotrophic respiration and autotrophic respiration in the subtropical forests of China

There is evidence of large differences in the spatial and temporal variations between soil heterotrophic respiration and autotrophic respiration in terrestrial ecosystems. This study was designed to test the hypothesis that there were differences in the seasonal and inter-annual variations between heterotrophic respiration and autotrophic respiration in subtropical forestlands. Here, we applied calibrated heterotrophic respiration and autotrophic respiration models to estimate soil respiration over 2002-2022 at three forest sites in subtropical China. Our results showed smaller seasonality and inter-annual variability in heterotrophic respiration than in autotrophic respiration. The inter-annual variation was strongest in winter for both heterotrophic respiration and autotrophic respiration. The main driving factor responsible for temporal variations was soil temperature for heterotrophic respiration, but fine root biomass for autotrophic respiration. There was a significant increasing trend only in autotrophic respiration over 2002-2022, which corresponded to the significant increasing trend in fine root biomass. Divergent inter-annual changes in these two respiration components led to the significant increasing trend in autotrophic respiration’ contribution, as well as total soil respiration. Due to the decreasing seasonality of soil temperature and fine root biomass, there was a declining seasonality in both heterotrophic respiration and autotrophic respiration. Our results highlight the importance of separately modeling and estimating soil heterotrophic respiration and autotrophic respiration in subtropical forestlands.