Impact of priming on global soil carbon stocks

Abstract

Fresh carbon input (above and belowground) contributes to soil carbon sequestration, but also accelerates decomposition of soil organic matter through biological priming mechanisms. Currently, poor understanding precludes the incorporation of these priming mechanisms into the global carbon models used for future projections. Here, we show that priming can be incorporated based on a simple equation calibrated from incubation and verified against independent litter manipulation experiments in the global land surface model, ORCHIDEE. When incorporated into ORCHIDEE, priming improved the model's representation of global soil carbon stocks and decreased soil carbon sequestration by 51% (12 ± 3 Pg C) during the period 1901-2010. Future projections with the same model across the range of CO and climate changes defined by the IPCC-RCP scenarios reveal that priming buffers the projected changes in soil carbon stocks - both the increases due to enhanced productivity and new input to the soil, and the decreases due to warming-induced accelerated decomposition. Including priming in Earth system models leads to different projections of soil carbon changes, which are challenging to verify at large spatial scales.

Interactive effects on organic matter processing from soils to the ocean: are priming effects relevant in aquatic ecosystems?

“…Even moderate changes in degradation rates can affect the C sequestration and ultimately the dynamics of the C-climate system. A first attempt to implement soil PE into Earth System models has revealed a prospective 51% reduction in C sequestration in soils during 1901-2010 linked to PEs (Guenet et al, 2018). These results in soils highlight the potential ecological relevance of non-additive effects on OM degradation rates.…”

Lagged effects dominate the inter-annual variability of the 2010–2015 tropical carbon balance

“…We generally found that the computational costs required to meet MHMCMC convergence criterion reported by Bloom & Williams (2015) for each 4°×5° grid-cell were prohibitively expensive. We 295 updated the adaptive MHMCMC to the Haario et al, (2001) MHMCMC approach, where the MHMCMC proposal distribution is adapted as a function of previously accepted samples (see Haario et al, 2001 for algorithm details). We ran 4 adaptive MHMCMC chains for 10 8 iterations in each 4°×5° grid-cell.…”

ORCHIDEE MICT-LEAK (r5459), a global model for the production, transport and transformation of dissolved organic carbon from Arctic permafrost regions, Part 1: Rationale, model description and simulation protocol

“…1m) MICT-L also incorporates a scheme for the 'priming' of organic matter decomposition, a process in which the relative stability of SOC is impacted by the intrusion of or contact with SOC of greater reactivity, resulting in enhanced rates of decomposition. This was first introduced by Guenet et al (2016) and updated in Guenet et al (2018). This process has shown itself to be of potentially large significance for SOC stocks and their respiration in high latitude regions, in empirical in situ and soil incubation studies (De Baets et al, 2016;Walz et al, 2017;Wild et al, 2014Wild et al, , 2016Zhang et al, 2017), as well as modelling exercises (Guenet et al, 2018).…”

“…This was first introduced by Guenet et al (2016) and updated in Guenet et al (2018). This process has shown itself to be of potentially large significance for SOC stocks and their respiration in high latitude regions, in empirical in situ and soil incubation studies (De Baets et al, 2016;Walz et al, 2017;Wild et al, 2014Wild et al, , 2016Zhang et al, 2017), as well as modelling exercises (Guenet et al, 2018). Here, priming of a given soil pool is represented through the decomposition of soil carbon (dSOC/dt) by the following equation :…”

“…To this end, we take a specific version of the terrestrial component of the IPSL global Earth System model (ESM) ORCHIDEE (Organising Carbon and Hydrology In Dynamic Ecosystems), one that is specifically coded for, calibrated with and evaluated on high latitude phenomena and permafrost processes, called ORCHIDEE-MICT (Guimberteau et al, 2018). This code is then adapted to include DOC production in the soil (ORCHIDEE-SOM, (Camino-Serrano et al, 2018)), 'priming' of SOC (ORCHIDEE-PRIM, (Guenet et al, 2016(Guenet et al, , 2018) and the riverine transport of DOC and CO2, including in-stream transformations, carbon and water exchanges with wetland soils and gaseous exchange between river surfaces and the atmosphere (ORCHILEAK, (Lauerwald et al, 2017)). The resulting model, dubbed ORCHIDEE MICT-LEAK, herafter referred to as MICT-L for brevity, is therefore able to represent: (a) Permafrost soil and snow physics, thermodynamics to a depth of 38m and dynamic soil hydrology to a depth of 2m; (b) Improved representation of biotic stress response to cold, heat and moisture in high latitudes; (c) Explicit representation of the active layer and frozen-soil hydrologic barriers; buildup of soil carbon stocks via primary production and vertical translocation (turbation) of SOC and DOC; (d) DOC leaching from tree canopies, atmospheric deposition, litter and soil organic matter, its adsorption/desorption to/from soil particles, its transport and transformation to dissolved CO2 (CO * 2(aq.))…”