Tracing soil respiration and its source across tropical peatland microtopographies and vegetation covers

Soil respiration (CO₂ effluxes) is a critical component for land-based greenhouse gas (GHG) monitoring, reporting and modelling. In organic matter-rich tropical peatlands, soil respiration magnitudes and variability are driven by belowground live root density (autotrophic) with substantial contribution of peat oxidation via microbial activity (heterotrophic). Moreover, other seasonally characterised environmental factors affect soil respiration dynamics such as hydrological condition, temperature and soil moisture. Yet, the respective contribution of autotrophic and heterotrophic to total soil respiration may vary between sites, vegetation covers, and microtopography profiles in tropical peatlands, leading to GHG reporting uncertainty. Clarifying the contribution heterotrophic activity will therefore provide a better understanding of the effect of peatland restoration or drainage on soil CO₂ effluxes reduction or increase, respectively. Here, we present and discuss soil respiration measurements taken across two different microtopography (hummock and hollow) and three land covers (natural forest, retired Acacia plantation, and shrubland) in tropical peatlands of Tri Pupa Jaya, South Sumatra, Indonesia over wet and dry seasons of 2022. We used a trenching approach (live root free peat plot) and complementary with carbon stable isotope (¹³C-CO₂) sampling across 27 paired measurement plots to determine the proportion of their autotrophic and heterotrophic contributions. Our preliminary findings suggest that autotrophic and heterotrophic soil respiration substantially vary across plots located in the hummock compared to hollow microtopography, with higher soil respiration observed at hummock compared to hollow microtopography, suggesting dominant root distribution forming higher elevations and generating higher autotrophic respiration in the hummock microtopography. Soil respiration from the trenched plots, was typically lower by 14–42% compared to untrenched plots and this pattern is consistent with the carbon stable isotope signatures. This study will help improve the current understanding of the driving mechanism and factors controlling magnitudes of soil respiration in tropical peatlands, particularly in assessing the impacts of both peatland restoration and drainage toward soil CO₂ efflux dynamics.