Chronological Molecular Fingerprint of Wetland Soil by Sensitivity-Enhanced Solid-State NMR

Abstract

Soil organic matter (SOM) plays a major role in mitigating greenhouse gas emission and thereby regulating Earth’s climate, carbon and water cycles, and biodiversity. Wetland soils contain the highest stores of soil carbon on the planet on an areal basis, accounting for one-third of all the SOM, yet our understanding of carbon sequestration within wetlands lags behind that of upland soils. Here we show the molecular-level fingerprints of wetland soils spanning eleven centuries using advanced solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Remarkably, combining dynamic nuclear polarization (DNP) with SOM enrichment allowed up to an 8,000-fold time-saving over conventional NMR approaches. This innovative approach for SOM characterization revealed that the parent herbaceous plant core molecular structures are preserved, with the aromatic and carbohydrate motifs becoming tightly packed, even after a millennium. Such preserved cores occur alongside molecules from the decomposition of loosely packed parent biopolymers and biogeochemical processing driven by geological global and anthropogenic changes, adding to the chemical diversity of SOM. These findings reveal that particulate organic matter (POM) should be a major focus for wetlands, and other soils with high organic matter content, especially when considering the fate of coastal wetland SOM when exposed to oxygenated water due to erosion.