Oxygen-starved places such as marshes and in floodplains accumulate carbon

Shunned by microbes, organic carbon can resist breakdown in underground environments

Posted: 01 May 2017 08:26 AM PDT

Organic matter whose breakdown would yield only minimal energy for hungry microorganisms preferentially builds up in floodplains, illuminating a new mechanism of carbon sequestration, a new study reveals….

…The soils and sediments beneath our feet can contain an astonishing amount of carbon — more than in all of the world’s plants and the atmosphere combined — and represents a significant potential source of the greenhouse gas carbon dioxide.

In a new study, Stanford scientists have uncovered a previously unknown mechanism that explains why microbes sometimes fail to break down all the plant and animal matter, leaving carbon underfoot. Understanding where, and how long, this buried organic matter lingers is crucial for scientists and policymakers to better predict and respond to climate change.

In oxygen-starved places such as marshes and in floodplains, microorganisms do not equally break down all of the available organic matter, the study shows. Instead, carbon compounds that do not provide enough energy to be worthwhile for microorganisms to degrade end up accumulating. This passed-over carbon, however, does not necessarily stay locked away below ground in the long run. Being water soluble, the carbon can seep into nearby oxygen-rich waterways, where microbes readily consume it.

To date, models of local ecosystems and broader climate change have failed to take into account this newfound carbon preservation mechanism, having focused chiefly on microbial enzymes and the availability of other elements for organic matter breakdown.

Kristin Boye, Vincent Noël, Malak M. Tfaily, Sharon E. Bone, Kenneth H. Williams, John R. Bargar, Scott Fendorf. Thermodynamically controlled preservation of organic carbon in floodplains. Nature Geoscience, 2017; DOI: 10.1038/ngeo2940