Falling water tables reduce peatland semiconductor minerals' capacity for preserving carbon

Abstract

AbstractSemiconductor minerals in peatland play a significant role in the stability of the soil carbon pool. Nevertheless, the ecosystem‐scale importance of semiconductor minerals distribution and their influence on carbon stability in peatlands is still to be determined. Therefore, this study investigated the spatial distribution of semiconductor minerals and their photoelectrochemical activity (PA) in three peatlands with distinct water tables (Equisetum‐swamp [−2.0 cm], Caltha‐meadow [−8.0 cm], and Carex‐meadow [−13.8 cm]). The results indicate that the peatlands of the Qinghai‐Tibet Plateau mainly contain hematite (4.64 wt%), brookite (0.71 wt%), baddeleyite (0.23 wt‰), and zincite (0.10 wt‰); hematite content is the main mineral in peatland. And significantly increased with the decrease of the water table; the photoelectrochemical examination showed that the band gap of semiconductor minerals displayed Caltha‐meadow > Equisetum‐swamp > Carex‐meadow, and the carrier concentration displayed Carex‐meadow > Equisetum‐swamp > Caltha‐meadow, and Carex‐meadow exhibits a steady photocurrent density (0.3 μA/cm2) under light. This suggests that peat soils exhibit an improved photoelectric response with water table drawdown, which would promote the potential for soil carbon mineralization; structural equation model analysis showed that hematite had a significant positive effect on soil organic carbon (SOC), while the PA of semiconductor minerals had a significant negative effect on SOC. That is, semiconductor minerals can not only protect SOC by adsorption but also accelerate organic carbon mineralization by photo‐catalytic generation of reactive oxygen species. Therefore, the decrease in the water table increases the PA of semiconductor minerals, which will weaken the protective effect of semiconductor minerals on soil carbon through adsorption and other means.