A soil biogeochemical modeling based analysis of the dynamical environmental sensitivity of soil decomposition to whole soil profile warming

Abstract:

Soil organic carbon (SOC) is the largest actively cycled terrestrial carbon pool, and is vulnerable to environmental changes including warming. Given current global warming and projected future climate change, it is imperative to understand and assess how SOC will respond to these changes. We here used a new comprehensive microbe and mineral-surface explicit soil biogeochemical model incorporated with the E3SM land model to simulate soil carbon dynamics, and calibrated and evaluated the simulations with field observations from one of the few on-going whole-soil-profile-warming experiments, the LBNL TES SFA Warming Experiment at the Blodgett Experiment Forest in the Sierra Nevada Mountains, California. The experiment warmed the soils at the conifer forest site by 4ºC to 1m depth using inserted heating rods since late 2013, with adjacent ambient control plots for comparison. The dynamical model is applied to estimate soil carbon fluxes and stocks from control and heated plots, compared to field observations, and improve understanding of the warming effect on soil carbon dynamics. We compared model results to measured soil respiration and soil carbon stocks at 9 depths along the soil profile in response to 5 years of warming. We modeled about a 20% increase in surface CO₂ emissions that remained relatively consistent across the 5 years, and a close to 10% decrease in vertically-resolved soil carbon stocks. Our analysis indicates that soil respiration sensitivity to environmental factors, such as soil temperature and moisture, are interactive and dynamic. We discuss how various soil biogeochemical processes influence soil respiration, surface CO₂ fluxes, and vertically-resolved stocks in response to increased soil temperature.