Drivers of root and fungal litter decomposition: implications for soil carbon cycling

Abstract

Globally, soils contain more carbon (C) than vegetation and the atmosphere combined. Despite clear importance to the global C budget, estimates of C fluxes into and out of soils remain highly uncertain. Decomposition is the dominant process by which C is lost from soil, but most of what is known about the controls of this process comes from studies of leaf litter at the soil surface. My first two chapters explore factors affecting the decomposition of two common belowground litter types. Chapter one is a global meta-analysis of the drivers of fine root decomposition, and is the first to explore the effects of species-level traits in addition to climate and substrate chemistry. My second chapter describes an experiment characterizing the dynamics and chemical drivers of fungal necromass decomposition, an important and understudied flux of soil C. My final chapter focuses on the role of soil fungi in the formation of “stabilized” soil C in the form of mineral associated organic matter (MAOM). Here, I call into question the current assumption that new MAOM formation in soil occurs in close proximity to root surfaces. Using quantitative estimates of fungal exploration, I put forth the hypothesis that fungal hyphae play an underappreciated role in distributing C through soil, and that hyphal contact with minerals encourages the formation of MAOM. This work suggests that current potential for MAOM formation in soils is significantly underestimated by not accounting for the impact of fungi.