Photosynthetic limits on carbon sequestration in croplands

A - Papers appearing in refereed journals

Janzen, H. H., Van Groenigen, K. J., Powlson, D. S., Schwinghamer, T. and Van Groenigen, J. W. 2022. Photosynthetic limits on carbon sequestration in croplands. Geoderma. 416 (15 June), p. 115810.

AuthorsJanzen, H. H., Van Groenigen, K. J., Powlson, D. S., Schwinghamer, T. and Van Groenigen, J. W.

How much C can be stored in agricultural soils worldwide to mitigate rising CO2 concentrations, and at what cost? This question, because of its critical relevance to climate policy, has been a focus of soil science for decades. The amount of additional soil organic C (SOC) that could be stored has been estimated in various ways, most of which have taken the soil as the starting point: projecting how much of the SOC previously lost can be restored, for example, or calculating the cumulative effect of multiple soil management strategies. Here, we take a different approach, recognizing that photosynthesis, the source of C input to soil, represents the most fundamental constraint to C sequestration. We follow a simple “Fermi approach” to derive a rough but robust estimate by reducing our problem to a series of approximate relations that can be parameterized using data from the literature. We distinguish two forms of soil C: ‘ephemeral C’, denoting recently-applied plant-derived C that is quickly decayed to CO2, and ‘lingering C’, which remains in the soil long enough to serve as a lasting repository for C derived from atmospheric CO2. First, we estimate global net C inputs into lingering SOC in croplands from net primary production, biomass removal by humans and short-term decomposition. Next, we estimate net additional C storage in cropland soils globally from the estimated C inputs, accounting also for decomposition of lingering SOC already present. Our results suggest a maximum C input rate into the lingering SOC pool of 0.44 Pg C yr-1, and a maximum net sequestration rate of 0.14 Pg C yr-1 – significantly less than most previous estimates, even allowing for acknowledged uncertainties. More importantly, we argue for a re-orientation in emphasis from soil processes towards a wider ecosystem perspective, starting with photosynthesis.  

KeywordsCarbon sequestration ; Photosynthesis ; Croplands ; Decomposition
Year of Publication2022
Journal citation416 (15 June), p. 115810
Digital Object Identifier (DOI)
Open accessPublished as ‘gold’ (paid) open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeS2N - Soil to Nutrition - Work package 1 (WP1) - Optimising nutrient flows and pools in the soil-plant-biota system
Publisher's version
Accepted author manuscript
Supplemental file
Output statusPublished
Publication dates
Online15 Mar 2022
Publication process dates
Accepted03 Mar 2022
PublisherElsevier Science Bv

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