Evaluating Environmental Influences on Grassland Soil Organic Carbon Temporal and Spatial Distribution

Abstract

The soil is the largest terrestrial carbon sink, and soil organic carbon (SOC) accounts for twice as much carbon as is stored in the atmosphere. A large portion of recent atmospheric carbon increases is due to the loss of carbon from soil. There are significant uncertainties as to the degree in which environmental factors influence SOC dynamics. A better understanding of how SOC is influenced by environmental factors is needed to inform global carbon budgets, climate projections, and analyses of SOC-climate change feedbacks. In this report, we analyzed SOC data from grassland sites across Oklahoma, USA to evaluate the relationships between soil carbon and environmental factors. We found SOC is more strongly influenced by soil-climate, particularly soil moisture, compared to climate data. Including soil-climate data in soil carbon predictions resulted in more accurate SOC predictions and indicate that soil moisture was the climate-related variable with the greatest influence on SOC. We also found that changes in SOC over time are significantly influenced by the initial SOC and soil depth. Vertical distribution of SOC in these soil profiles became more stratified during the study period, with the SOC in the top 5 cm increasing in relation to SOC at deeper depths.