Leveraging microbiome-climate interactions to quantify the relative sequestration potential of stable soil organic carbon across US rangelands

Soil organic carbon (SOC) sequestration within agricultural and grazed lands is recognized as a major terrestrial sink for carbon globally. It's an imperative tool to counterbalance greenhouse gas (GHG) emissions and alleviate global change. Efficient investment and land management hinge on understanding where the greatest SOC sequestration potential lies. The significance of microbial communities as broad-scale determinants of SOC sequestration—particularly within stable SOC pools such as mineral-associated organic carbon (MAOC)—is increasingly recognized in recent research. In this study, we have pioneered a novel reduced complexity model (RCM) that harmonizes well-established biogeochemical cycling with emergent insights on microbially-derived carbon assimilation, microbial community adaptation to historical climate patterns, and MAOC saturation. This model was utilized to construct a gridded map of sequestration potential in the US rangelands. The model incorporates 30-year historical climate averages, vegetation cover, type, net primary productivity, weekly soil moisture, daily soil temperature, MAOC saturation, along with soil texture, bulk density`, field capacity, and pH to estimate the relative potential SOC sequestration (ton C ha^-1 yr^-1) over the forthcoming decades. While the model's primary application is for relative SOC sequestration potentials, we validated it by comparing both relative and absolute values with empirical rates from the literature and previous SOC sequestration potential assessments. The predicted absolute rates of SOC sequestration potential align with literature, ranging from 0.01 - 2.4 ton C ha^-1 yr^-1, with mean state-wide rates of 0.05 - 0.1 across the western US. Locations with predominantly tree or perennial grass vegetation types generally exhibit higher relative sequestration rate potential than those dominated by annual grasses/forbs and shrubs, with substantial variation attributed to historical mean annual precipitation, weekly soil moisture, and daily soil temperature.

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