Chemical Characterization of the Degradation of Necromass from Four Ascomycete Fungi: Implications for Soil Organic Carbon Turnover and Storage

Abstract

Terrestrial soils store approximately twice as much carbon as is currently in the atmospheric CO2 pool. Despite its importance in the global carbon cycle, much is still unknown about the source, turnover, and stability of the soil organic matter (SOM) pool. For example, fungi are known to play an important role in shaping the chemistry of SOM by degrading common biopolymers, and fungal biomass has been found to be a significant portion of living microbial SOM, dominating over bacteria in some soils by as much as 90%. And yet, despite growing evidence that microbial necromass, or dead microbial tissue, may be a larger contributor to SOM than previously thought, very little is known about the specific degradation patterns of fungal necromass, and subsequently its potential chemical contributions to long-lived SOM pools. This study addresses these knowledge gaps through a time-series analysis of the degradation patterns of fungal tissue from four different saprotrophic Ascomyota species in temperate restored prairie soils. Fungal tissue was buried in a temperate soil and harvested at intervals from 1 day to one month. After harvest, chemical analysis of the dried tissue by thermochemolysis pyrolysis-GCMS was used for relative quantitation of compounds derived from lipids, aromatics, carbohydrates, nitrogen-containing, and unspecified residues. The degradation of these specific molecules, bulk fungal tissue, and bulk C and N within the tissue, is modeled to (1) show that a small portion of fungal necromass persists in the environment even after the period of the experiment and could serve as a contributor to long-lived SOM, and (2) provide quantitative information on the contribution of fungal tissue to global SOM pools.