Hierarchical saturation of soil carbon pools near a natural CO₂ spring

Authors: KOOL, DORIEN M.; CHUNG, HAEGEUN¹; TATE, KEVIN R.²; ROSS, DES J.²; NEWTON, PAUL C. D.³; SIX, JOHAN¹

Source: Global Change Biology, Volume 13, Number 6, June 2007 , pp. 1282-1293(12)

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Abstract:

Soil has been identified as a possible carbon (C) sink to mitigate increasing atmospheric CO₂ concentration. However, several recent studies have suggested that the potential of soil to sequester C is limited and that soil may become saturated with C under increasing CO₂ levels. To test this concept of soil C saturation, we studied a gley and organic soil at a grassland site near a natural CO₂ spring. Total and aggregate-associated soil organic C (SOC) concentration showed a significant increase with atmospheric CO₂ concentration. An asymptotic function showed a better fit of SOC and aggregation with CO₂ level than a linear model. There was a shift in allocation of total C from smaller size fractions to the largest aggregate fraction with increasing CO₂ concentration. Litter inputs appeared to be positively related to CO₂ concentration. Based on modeled function parameters and the observed shift in the allocation of the soil C from small to large aggregate-size classes, we postulate that there is a hierarchy in C saturation across different SOC pools. We conclude that the asymptotic response of SOC concentration at higher CO₂ levels indicates saturation of soil C pools, likely because of a limit to physical protection of SOC.

Keywords: C sink; elevated CO2; grassland; hierarchy; soil aggregation; soil carbon dynamics; soil carbon modeling; soil carbon saturation; soil carbon sequestration; soil stability

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2486.2007.01362.x

Affiliations: 1: Department of Plant Sciences, University of California, Davis, CA 95616, USA, 2: Landcare Research, Private Bag 11052, Palmerston North, New Zealand, 3: Land and Environmental Management Group, AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand

Publication date: 2007-06-01