Soil Carbon Sequestration: New Insights into a Key Issue

Global estimates show that soils store more carbon than the atmosphere and plants combined. Despite the obvious importance of soils in global carbon cycling, there remain critical gaps in our knowledge of the sequestration of long-lived carbon stores. Fungi constitute a major portion of belowground biomass and thus the decomposition of their dead tissues (or necromass) should be an important contributor to soil carbon sequestration. The exact mechanism(s) by which fungal necromass is decomposed and the flow of fungal molecules into soil carbon pools remain poorly understood.  Our studies have focused on the degradation of fungi and their role in carbon sequestration in tall-grass prairie systems.

Our studies have shown that fungal necromass degradation (or decomposition) is a dynamic process. Most of the necromass (~80%) tends to be lost within the first week in the soil (i.e. a soluble or fast pool), while the residue maintains a constant mass for the remainder of the time in the soil (insoluble or slow pool).  During that first week, chitin from fungal cell walls was rapidly lost. This initial degradation was driven by the Zygomycete Mortierella, which is known to degrade chitin. The abundance of Mortierella was positively correlated with both the rapid loss of chitin, and increases in levels of ergosterol (a fungal sterol) and n-acetyl-glucosaminidase, a chitin-degrading enzyme. In the slow pool, levels of certain lipids (nC24, nC18) were unchanged or increased in concentration during tissue degradation. Our research now focuses on the insoluble material, which we believe is important to carbon sequestration. Our next step is to trace the pathway of fungal molecules from necromass to soil particles.