Roots Accelerate Both Soil Carbon Stabilization and Loss

The Science

Small changes in the relative rates of soil carbon formation (via interactions with soil minerals) and loss (via microbial respiration, or breathing) affect carbon dioxide concentrations in the atmosphere. Predicting these rates is challenging because they are influenced by so many factors simultaneously—type of mineral in the soil, species of microbes present, and chemistry of new carbon inputs via plant litterfall and root exudation. Researchers constructed artificial root-soil systems to independently manipulate these factors and found that roots control soil carbon content by accelerating respiration and carbon stabilization simultaneously.

The Impact

Better managing soils to store more carbon can mitigate some of climate change’s worst effects. Efforts to enhance soil carbon content often focus on stabilization processes (i.e., the formation of long-lived types of carbon tightly bound to clay minerals). However, research shows that formation of “stable” soil carbon does not necessarily increase the total amount of carbon in soil. The processes that enhance carbon stabilization also increase microbial respiration (carbon loss). This information is relevant for land managers seeking to build carbon stocks.

Summary

A team of researchers constructed artificial root-soil systems to independently manipulate the:

• Reactivity of clay minerals;
• Structure of microbial communities (fungal vs. bacterial dominated);
• Presence or absence of artificial roots; and
• Chemistry of fresh carbon inputs (monosaccharide, disaccharide, or polysaccharide).

These factors have all been identified as important controls on soil carbon cycling but are often highly interlinked in real soils, which makes quantifying their individual effects difficult. The dominant control on the size of the soil carbon pool is an interaction between mineral reactivity and root exudation. Root exudates promote destabilization of mineral-associated carbon in weakly active clays but accelerate the formation of mineral-associated carbon in soils with highly reactive iron oxides. However, higher rates of carbon stabilization do not always result in larger soil carbon pools because the same factors that tend to promote mineral-associated carbon formation also accelerate respiratory carbon losses.

Principal Investigator

Bonnie Waring
Imperial College London
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was funded by the Biological and Environmental Research (BER) program within the U.S. Department of Energy’s Office of Science under award DE-SC0020108.

References