Estimation of annual soil CO 2 efflux under the erosion and deposition conditions by measuring and modeling its respiration rate in southern China.

Soil respiration (Rs) is a crucial ecological process of carbon (C) cycling in the terrestrial ecosystems, and soil erosion has a significant impact on its C budget and balance. However, the variations of Rs rate and their CO ₂ efflux induced by erosion are currently poorly understood. To this end, four landscape positions (top, up, middle and toe) with different erosional and depositional characteristics were selected on a typical eroded slope in southern China to conduct field experiments, aiming to explore the effects of erosion and deposition on Rs among various sites. From March 2021 to February 2022, the in-situ Rs were measured using an automated soil respiration system, together with soil temperature at 5 cm depth (T _s5 ) and water content at 10 cm depth (SWC ₁₀ ). We initially constructed various Rs models across a one-year period, based on its relationships with T _s5 and SWC ₁₀ . Subsequently, the seasonal changes of Rs at different erosional sites were simulated by the optimum models, and their annual CO ₂ fluxes were further estimated. The results showed that Rs rates at all sites displayed a bimodal seasonal pattern, with the highest values in May and August. And the measured Rs of the eroding and depositional sites were 0.05-7.71 and 1.47-13.03 μmol m ^-2  s ^-1 , respectively. Also, remarkably higher T _s5 and SWC ₁₀ were observed in depositional sites versus the eroding sites (P < 0.05). Additionally, Rs rates at all sites were positively correlated with SOC and T _s5 , but negatively correlated with SWC ₁₀ . Herein, Rs models to single- and double-variable were established at different positions, and we found that the fitted R ² and AIC differed on various sites, primarily in erosional and depositional sites. Furthermore, through the best-fitting models (higher R ² and lowest AIC) we screened, the average Rs values of 3.03 and 4.46 μmol m ^-2  s ^-1 were quantitatively estimated for the eroding and depositional sites, respectively. Finally, it could be further assessed that the mean annual soil CO ₂ -C efflux of eroded site (1104.14 g m ^-2 ) was significantly lower than that of depositional site (1629.46 g m ^-2 ). These findings highlighted the effect of erosion and deposition on Rs, which will facilitate a better understanding of C cycling in terrestrial ecosystems.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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