Abstract
Quantifying the upper limit of stable soil carbon storage is essential for guiding policies to increase soil carbon storage. One pool of carbon considered particularly stable across climate zones and soil types is formed when dissolved organic carbon sorbs to minerals. We quantified, for the first time, the potential of mineral soils to sorb additional dissolved organic carbon (DOC) for six soil orders. We compiled 402 laboratory sorption experiments to estimate the additional DOC sorption potential, that is the potential of excess DOC sorption in addition to the existing background level already sorbed in each soil sample. We estimated this potential using gridded climate and soil geochemical variables within a machine learning model. We find that mid- and low-latitude soils and subsoils have a greater capacity to store DOC by sorption compared to high-latitude soils and topsoils. The global additional DOC sorption potential for six soil orders is estimated to be 107 pm 13 Pg C to 1 m depth. If this potential was realized, it would represent a 7% increase in the existing total carbon stock.
Highlights
Carbon (C) inputs to soil, much of it in the form of dissolved organic carbon (DOC), are expected to increase from CO2 fertilization (Drake et al 2011; Jiang et al 2020; Palmroth et al 2006) and improved management practices (Cardinael et al 2018; Maillard et al 2017; Poeplau and Don2015) such as those outlined in the ‘4 per 1000’ initiative, which aims at removing atmospheric CO2 by increasing soil C sequestration with an emphasis on long-term storage (Minasny et al 2017)
This study provides an estimate of the potential additional C that could be sorbed to minerals in soils spanning six soil orders and a range of climate conditions globally
Our best estimate of 107 Pg C should be interpreted as the maximum of additional C that can potentially be sorbed as DOC
Summary
Carbon (C) inputs to soil, much of it in the form of DOC, are expected to increase from CO2 fertilization (Drake et al 2011; Jiang et al 2020; Palmroth et al 2006) and improved management practices (Cardinael et al 2018; Maillard et al 2017; Poeplau and Don2015) such as those outlined in the ‘4 per 1000’ initiative, which aims at removing atmospheric CO2 by increasing soil C sequestration with an emphasis on long-term storage (Minasny et al 2017). Warming soils are likely to experience increased decomposition of particulate organic matter, leading to some increase in DOC production (Bengtson and Bengtsson 2007; Fu et al 2019; Reynolds and Fenner 2001). This additional DOC can be lost through decomposition or runoff, or can sorb to mineral particles as it percolates down the soil column (Kaiser and Kalbitz 2012) thereby increasing the size of the total soil C pool with long-term storage characteristics. During the 1970s and 1980s, soil organic matter was thought to be stable to the extent that it contained chemically recalcitrant compounds (Kogel-Knabner 1986; Biogeochemistry (2021) 152:127–142
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