Evaluating permanganate oxidizable carbon (POXC)'s potential for differentiating carbon pools in wetland soils

Soil carbon (C) storage is a globally important ecosystem service with the potential to contribute to climate change mitigation. Wetlands are heavily researched hot spots for soil C storage. Despite the growing number of wetland soil C inventories, most studies focus only on total C quantification; there is limited application of methods that evaluate differences in C stability and vulnerability to mineralization within the C pool. Permanganate oxidizable C (POXC) is a well-established soil health indicator in agriculture shown to be sensitive to changing conditions or management regimes and may prove equally informative in wetland studies. This research quantified POXC in six diverse wetland soils that differed greatly in organic matter content and spanned both freshwater and saltwater habitats, then evaluated the relationship between POXC and basic soil C properties, microbial indicators, and physical and chemical fractionation metrics. Results showed POXC averaged similar to 37 times greater in wetlands than upland agricultural soils, but was less robust in differentiating between individual wetlands than total C or organic matter content. Rather, the ratio of POXC to soil organic C may be a more informative metric for evaluating the proportion of slightly processed C in wetland soils. Significant correlations were found between POXC and almost all other soil properties measured, suggesting POXC could be a rapid, reliable, and economical proxy for other analyses. Overall, POXC shows potential for providing novel information about wetland soil C stability, but requires additional research to improve interpretability. Applying POXC analysis in time series data collection and before-after-control impact experiments may be particularly informative for wetland management.