Molecular and Microscopic Insights into the Formation of Soil Organic Matter in a Red Pine Rhizosphere

James Harsh,Zhenqing Shi,Rosalie Chu,Alex Crump,C. Keller,Colin Brislawn,Tamas Varga,Linda Thomashow,Malak Tfaily,A. Smith,Alice Dohnalkova

doi:10.3390/soils1010004

Abstract

Microbially-derived carbon inputs to soils play an important role in forming soil organic matter (SOM), but detailed knowledge of basic mechanisms of carbon (C) cycling, such as stabilization of organic C compounds originating from rhizodeposition, is scarce. This study aimed to investigate the stability of rhizosphere-produced carbon components in a model laboratory mesocosm of Pinus resinosa grown in a designed mineral soil mix with limited nutrients. We utilized a suite of advanced imaging and molecular techniques to obtain a molecular-level identification of newly-formed SOM compounds, and considered implications regarding their degree of long-term persistence. The microbes in this controlled, nutrient-limited system, without pre-existing organic matter, produced extracellular polymeric substances that formed associations with nutrient-bearing minerals and contributed to the microbial mineral weathering process. Electron microscopy revealed unique ultrastructural residual signatures of biogenic C compounds, and the increased presence of an amorphous organic phase associated with the mineral phase was evidenced by X-ray diffraction. These findings provide insight into the formation of SOM products in ecosystems, and show that the plant- and microbially-derived material associated with mineral matrices may be important components in current soil carbon models.

Highlights

Soils play a critical role in global carbon cycling, having a dynamic carbon reservoir in the form of soil organic matter (SOM) that is estimated to be four times larger than the amount stored in the atmosphere [1,2]
The error bars are within extractions, amorphous material remained associated with the minerals
Our main findings were:red (a) pine soil microorganisms initially column experiment were residence times, (b)and a significant plantand microbially-derived was contributed to able to transform stabilize amount red pineofroot exudates into a variety of Cbiomass compounds with varying the mineral matrix, and (c) residual microbial biomass stayed in the system even after extraction of projected residence times, (b) a significant amount of plant- and microbially-derived biomass was soil mineralstowith solvents

Summary

Introduction

Soils play a critical role in global carbon cycling, having a dynamic carbon reservoir in the form of soil organic matter (SOM) that is estimated to be four times larger than the amount stored in the atmosphere [1,2]. In 2010, a new conceptual framework for a microbial carbon pump was proposed for the microbial production of recalcitrant non-living organic matter and the storage of fixed C in. New research on microbial carbon stabilization in soils has emerged, focusing on SOM molecular structure characterization, recalcitrance, and persistence [6–8], as well as studies showing the importance of microbially-derived C for stabilized. Understanding the dynamics of C pools in soil systems is critical for controlling atmospheric carbon dioxide levels and maintaining soil health and agricultural productivity. Microorganisms add carbon to soil through rapid and persistent cell division, community growth, exudation of biogenic products, and cell death [12]

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