Tracing the sources and spatial distribution of organic carbon in subsoils using a multi-biomarker approach.

Gerrit Angst,Stephan John,Carsten W Mueller,Ingrid Kögel-Knabner,Janet Rethemeyer

doi:10.1038/srep29478

Abstract

Soil organic carbon (SOC) from aboveground and belowground sources has rarely been differentiated although it may drive SOC turnover and stabilization due to a presumed differing source dependent degradability. It is thus crucial to better identify the location of SOC from different sources for the parameterization of SOC models, especially in the less investigated subsoils. The aim of this study was to spatially assess contributions of organic carbon from aboveground and belowground parts of beech trees to subsoil organic carbon in a Dystric Cambisol. Different sources of SOC were distinguished by solvent-extractable and hydrolysable lipid biomarkers aided by 14C analyses of soil compartments <63 μm. We found no effect of the distance to the trees on the investigated parameters. Instead, a vertical zonation of the subsoil was detected. A high contribution of fresh leaf- and root-derived organic carbon to the upper subsoil (leaf- and root-affected zone) indicate that supposedly fast-cycling, leaf-derived SOC may still be of considerable importance below the A-horizon. In the deeper subsoil (root-affected zone), roots were an important source of fresh SOC. Simultaneously, strongly increasing apparent 14C ages (3860 yrs BP) indicate considerable contribution of SOC that may be inherited from the Pleistocene parent material.

Highlights

Soil organic carbon (SOC) from aboveground and belowground sources has rarely been differentiated it may drive soil organic carbon (SOC) turnover and stabilization due to a presumed differing source dependent degradability
The SOC stored at greater soil depths has been found to generally feature low 14C contents that decrease with increasing depth[2,4,5]
Because subsoils are commonly unsaturated in organic carbon (OC) and microbial activity has been found to be low[7,8], some authors regarded subsoils as having the potential to sequester additional carbon[6,9]

Summary

Introduction

Soil organic carbon (SOC) from aboveground and belowground sources has rarely been differentiated it may drive SOC turnover and stabilization due to a presumed differing source dependent degradability. In forest soils, the input of SOC from aboveground and belowground vegetation parts may be strongly dependent on the distance to the trees[20] This spatial dimension has mostly been overlooked, and there have only been a few studies that involved the factor ‘distance’ in their sampling design. An influence of the distance to individual beech trees on the chemical composition of soil organic matter fractions and SOC contents was absent[22]. These studies did not differentiate aboveground and belowground sources of SOC. The authors found strong horizontal and vertical gradients in SOC from different plant sources mainly controlled by the rooting zone of individual trees

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Conclusion