title: Clay illuviation provides a long-term sink for C sequestration in subsoils.
abstract: Soil plays a key role in the global carbon (C) cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in microaggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation.
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.|Department of Biological Sciences, School of Natural Sciences, University of Limerick, Limerick, Republic of Ireland.
authors.forename: Gemma
authors.initials: G
authors.lastname: Torres-Sallan
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.|Farming Systems Ecology, Wageningen University and Research, Wageningen, The Netherlands.
authors.forename: Rogier P O
authors.initials: RP
authors.lastname: Schulte
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Lanigan
authors.affiliation: Department of Biological Sciences, School of Natural Sciences, University of Limerick, Limerick, Republic of Ireland.
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Byrne
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.
authors.forename: Brian
authors.initials: B
authors.lastname: Reidy
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.
authors.forename: Iolanda
authors.initials: I
authors.lastname: Simó
authors.affiliation: Department of Environmental Systems Science, Swiss Federal Institute of Technology, ETH Zurich, Zurich, Switzerland.
authors.forename: Johan
authors.initials: J
authors.lastname: Six
authors.affiliation: Teagasc, Johnstown Castle, Wexford, Republic of Ireland.|Soil Biology and Biological Soil Quality, Wageningen University and Research, Wageningen, The Netherlands.
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Creamer