Soil Fungal:Bacterial Ratios Are Linked to Altered Carbon Cycling.

Ashish A Malik,Veronika Schlager,Anna Oliver,Nico Jehmlich,Gerd Gleixner,Somak Chowdhury,Martin Von Bergen,Perla G M Vazquez,Robert I Griffiths,Jeremy Puissant

doi:10.3389/fmicb.2016.01247

Abstract

Despite several lines of observational evidence, there is a lack of consensus on whether higher fungal:bacterial (F:B) ratios directly cause higher soil carbon (C) storage. We employed RNA sequencing, protein profiling and isotope tracer techniques to evaluate whether differing F:B ratios are associated with differences in C storage. A mesocosm 13C labeled foliar litter decomposition experiment was performed in two soils that were similar in their physico-chemical properties but differed in microbial community structure, specifically their F:B ratio (determined by PLFA analyses, RNA sequencing and protein profiling; all three corroborating each other). Following litter addition, we observed a consistent increase in abundance of fungal phyla; and greater increases in the fungal dominated soil; implicating the role of fungi in litter decomposition. Litter derived 13C in respired CO2 was consistently lower, and residual 13C in bulk SOM was higher in high F:B soil demonstrating greater C storage potential in the F:B dominated soil. We conclude that in this soil system, the increased abundance of fungi in both soils and the altered C cycling patterns in the F:B dominated soils highlight the significant role of fungi in litter decomposition and indicate that F:B ratios are linked to higher C storage potential.

Highlights

The soil organic carbon (SOC) pool is larger than global vegetation and the atmospheric pool combined, and the exchanges of C between the soil and the atmosphere are quantitatively relevant for the terrestrial C cycle (Amundson, 2001; Lal, 2010)
We describe a mesocosm experiment that aimed to explicitly link microbial community differences, in soil F:B ratio, to the soil’s potential to store C
The soils were chosen based on PLFA-derived microbial community composition from 2007 (Lange et al, 2014), such that the soils were similar in their physical and chemical properties but differed in their microbial community structure, and their F:B ratio

Summary

INTRODUCTION

The soil organic carbon (SOC) pool is larger than global vegetation and the atmospheric pool combined, and the exchanges of C between the soil and the atmosphere are quantitatively relevant for the terrestrial C cycle (Amundson, 2001; Lal, 2010). Soil microorganisms due to their high biomass and activity largely control soil C cycling acting as gatekeepers for soil-atmosphere C exchange (Schimel and Schaeffer, 2012; Gleixner, 2013) This regulation is a result of a balance between the rate of microbial decomposition and stabilization of organic C in soil. Sequencing of total extracted RNA without amplifying specific rRNA regions gives a quantitative assessment of the taxonomic diversity of total microbial communities (Urich et al, 2008) This allows indexing of F:B ratios that is otherwise not possible with amplicon sequencing based taxonomic assays. Following the addition of 13C labeled plant litter to these soils, RNA sequencing and protein profiling were applied to assess changes in the taxonomic and functional characteristics of the microbial community. The tracer C was followed into microbial biomass, respired CO2 and soil organic matter to complete mass balance of the applied substrate and assess concomitant changes in C storage

MATERIALS AND METHODS

Experimental Setup

RESULTS

Findings

DISCUSSION