Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land-use

A - Papers appearing in refereed journals

Redmile-Gordon, M. A., Watts, C. W., Gregory, A. S. and White, R. P. 2020. Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land-use. Geoderma. 363 (1st April), p. 114143.

AuthorsRedmile-Gordon, M. A., Watts, C. W., Gregory, A. S. and White, R. P.
Abstract

While soil microbial ecology, soil organic carbon (SOC) and soil physical quality are widely understood to be interrelated — the underlying drivers of emergent properties, from land management to biochemistry, are hotly debated. Biological binding agents, microbial exudates, or ‘extracellular polymeric substances’ (EPS) in soil are now receiving increased attention due to several of the existing methodological challenges having been overcome. We applied a recently developed approach to quantify soil EPS, as extracellular protein and extracellular polysaccharide, on the well-characterised soils of the Highfield Experiment, Rothamsted Research, UK. Our aim was to investigate the links between agricultural land use, SOC, transient binding agents known as EPS, and their impacts on soil physical quality (given by mean weight diameter of water stable aggregates; MWD). We compared the legacy effects from long-term previous land-uses (unfertilised grassland, fertilised arable, and fallow) which were established >50 years prior to investigation, crossed with the same current land-uses established for a duration of only 2.5 years prior to sampling. Continuously fallow and grassland soils represented the poorest and greatest states of structural integrity, respectively. Total SOC and %N were found to be affected by both previous and current land-uses, while extractable EPS and MWD were driven primarily by the current land-use. Land-use change between these two extremes (fallow→grass; grass→fallow) resulted in smaller SOC differences (64% increase or 37% loss) compared to MWD (125% increase or 78% loss). SOC concentration correlated well to MWD (adjusted R2 = 0.72) but the high SOC content from previous grassland was not found to contribute directly to the current stability (p < 0.05). Our work thus supports the view that certain distinct components of SOC, rather than the total pool, have disproportionately important effects on a soil’s structural stability. EPS-protein was more closely related to aggregate stability than EPS-polysaccharide (p values of 0.002 and 0.027, respectively), and ranking soils with the 5 highest concentrations of EPS-protein to their corresponding orders of stability (MWD) resulted in a perfect match. We confirmed that both EPS-protein and EPS-polysaccharide were transient fractions: supporting the founding models for aggregate formation. We suggest that management of transient binding agents such as EPS —as opposed to simply increasing the total SOC content— may be a more feasible strategy to improve soil structural integrity and help achieve environmental objectives.

KeywordsTransient binding agents; Microbial exudates; Protein matrix bonding; Exopolysaccharide; Water stable aggregate (MWD); Cation exchange resin (CER)
Year of Publication2020
JournalGeoderma
Journal citation363 (1st April), p. 114143
Digital Object Identifier (DOI)doi:10.1016/j.geoderma.2019.114143
Web address (URL)https://www.sciencedirect.com/science/article/pii/S0016706119312091?via%3Dihub
Open accessPublished as ‘gold’ (paid) open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeThe Rothamsted Long Term Experiments [2017-2022]
Publisher's version
Accepted author manuscript
Copyright license
CC BY
Output statusPublished
Publication dates
Online14 Jan 2020
Publication process dates
Accepted14 Dec 2019
PublisherElsevier Science Bv
ISSN0016-7061

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