Aerobic and anaerobic potential microbial consumption of salt marsh soils organic matter

Abstract

Abstract Salt marshes have a high capacity to stabilize organic carbon in their soils as organic matter (OM). Globally, they are estimated to hold ~862 to 1,350 Tg of organic carbon in the upper meter. Which OM compounds are accumulated and which are the mechanisms protecting them, beyond anoxia, are important questions to unravel and understand the full potential of salt marsh ecosystems to store carbon. Soil microbial communities have a key role in OM degradation and, therefore, in its accumulation. In this study, performed at Ria de Aveiro (Portugal) coastal lagoon, two techniques were successfully applied to explore OM microbial mineralization in salt marsh soils: EcoPlatesTM under aerobic and anaerobic conditions, and Fourier-transform infrared spectroscopy (FTIR), together with principal component analysis on the transposed matrix, to extract the signal of specific compounds. The soil samples showed a high spatial homogeneity in microbial potential consumption, regarding both depth (up to 89 cm) and halophyte species. Potential aerobic consumption was high at all depths but the anaerobic communities showed a higher diversity in carbon sources consumption. Amino acids, carbohydrates and polymers were widely consumed, while half of the carboxylic acids were not consumed. Two of the carbon sources that were not consumed were likely protected within bigger molecules, D-galacturonic acids within hemicellulose and 4-hydroxy benzoic acids within phenolic compounds, being the last most likely accumulated as blue carbon. In addition, our study shows the potential of microbial incubations coupled with FTIR to greatly increase our understanding of salt marsh soils OM dynamics.