Reclamation of marshlands for agricultural land use is widespread. An example of large-scale land use shifts is evident in the Everglades Agricultural Area of Florida where freshwater wetlands were converted to sugarcane (Saccharum officinarum) production. Such land-use shifts can markedly influence soil organic matter cycling and processes. The effect of such land use change on molecular characteristics of soil organic carbon is unknown. In this study, three surface soils cores (0–5？cm, 5–10？cm, and 10–19？cm) from a representative marsh and a sugarcane field in the Florida Everglades with known land use history and management practices were characterized using pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) to investigate molecular characteristics of soil organic matter. Soil organic carbon (SOC), total nitrogen, total sulfur, and water extractable organic carbon contents in sugarcane soil were 37.02%, 2.44%, 0.46% and 0.11%, while they were 44.57%, 2.62%, 0.73% and 0.38%, respectively. On the whole, marshland reclamation to sugarcane caused increase of aromatics (from 11.37% to 13.20%), polyaromatic hydrocarbon(from 0% to 1.63%), n-alkanes (from 8.90% to 16.17%), n-alkenes (from 25.10% to 28.77%), other aliphatics (from 7.33% to 11.77%) and fatty acids (from 1.93% to 3.87%) in pyrolysis products of soil organic matter (SOM), whereas this shift reduced lignin (from 12.87% to 2.47%), phenols (from 23.33% to 16.13%), polysaccharides (from 2.40% to 1.03%), benzofuran (from 1.67% to 0.27) and nitrogen containing compounds (from 5.07% to 4.67%), respectively. Overall, the conversion of marsh to sugarcane land use not only reduced total SOC contents but also altered molecular features of SOM with significant increases in aliphatic fractions and almost complete exhaustion of lignin fractions, signifying SOC dynamic shift due to land change in the Everglades. 

Reclamation of marshlands for agricultural land use is widespread. An example of large-scale land use shifts is evident in the Everglades Agricultural Area of Florida where freshwater wetlands were converted to sugarcane (Saccharum officinarum) production. Such land-use shifts can markedly influence soil organic matter cycling and processes. The effect of such land use change on molecular characteristics of soil organic carbon is unknown. In this study, three surface soils cores (0–5？cm, 5–10？cm, and 10–19？cm) from a representative marsh and a sugarcane field in the Florida Everglades with known land use history and management practices were characterized using pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) to investigate molecular characteristics of soil organic matter. Soil organic carbon (SOC), total nitrogen, total sulfur, and water extractable organic carbon contents in sugarcane soil were 37.02%, 2.44%, 0.46% and 0.11%, while they were 44.57%, 2.62%, 0.73% and 0.38%, respectively. On the whole, marshland reclamation to sugarcane caused increase of aromatics (from 11.37% to 13.20%), polyaromatic hydrocarbon(from 0% to 1.63%), n-alkanes (from 8.90% to 16.17%), n-alkenes (from 25.10% to 28.77%), other aliphatics (from 7.33% to 11.77%) and fatty acids (from 1.93% to 3.87%) in pyrolysis products of soil organic matter (SOM), whereas this shift reduced lignin (from 12.87% to 2.47%), phenols (from 23.33% to 16.13%), polysaccharides (from 2.40% to 1.03%), benzofuran (from 1.67% to 0.27) and nitrogen containing compounds (from 5.07% to 4.67%), respectively. Overall, the conversion of marsh to sugarcane land use not only reduced total SOC contents but also altered molecular features of SOM with significant increases in aliphatic fractions and almost complete exhaustion of lignin fractions, signifying SOC dynamic shift due to land change in the Everglades.