Microbes, minerals and moisture, oh my! How abiotic and biotic interactions alter the molecular composition of organic matter

Soils have an enormous potential to retain carbon (C), predominantly due to sorption to mineral surfaces. Yet, mineral-bound C may be vulnerable to microbial decomposition in response to changes in temperature & moisture. Here I show that inhibition of CO₂ emissions from the combined effect of increased moisture content & clay is reflected in the turnover of key molecular signatures, such as the nominal oxidation state of C, often irrespective of temperature. I suggest that that microbial access to C is governed by mineral sorption & moisture content, & that C in wet soils is thermodynamically unfavorable for microbial consumption.