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| Titel |
Weathering by tree-root-associating fungi diminishes under simulated Cenozoic atmospheric CO2 decline |
| VerfasserIn |
J. Quirk, J. R. Leake, S. A. Banwart, L. L. Taylor, D. J. Beerling |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 2 ; Nr. 11, no. 2 (2014-01-23), S.321-331 |
| Datensatznummer |
250117145
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| Publikation (Nr.) |
 copernicus.org/bg-11-321-2014.pdf |
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| Zusammenfassung |
| Trees dominate terrestrial biotic weathering of silicate minerals by
converting solar energy into chemical energy that fuels roots and their
ubiquitous nutrient-mobilising fungal symbionts. These biological activities
regulate atmospheric CO2 concentrations ([CO2]a) over
geologic timescales by driving calcium and magnesium fluvial ion export and
marine carbonate formation. However, the important stabilising feedbacks
between [CO2]a and biotic weathering anticipated by
geochemical carbon cycle models remain untested. We report experimental
evidence for a negative feedback across a declining Cenozoic
[CO2]a range from 1500 to 200 ppm, whereby low
[CO2]a curtails mineral surface alteration via trenching and
etch pitting by arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal
partners of tree roots. Optical profile imaging using vertical scanning
interferometry reveals changes in nanoscale surface topography consistent
with a dual mode of attack involving delamination and trenching by AM and EM
fungal hyphae on phyllosilicate mineral flakes. This is consistent with field
observations of micropores in feldspar, hornblende and basalt, purportedly
caused by EM fungi, but with little confirmatory evidence. Integrating these
findings into a process-based biotic weathering model revealed that low
[CO2]a effectively acts as a "carbon starvation" brake,
causing a three-fold drop in tree-driven fungal weathering fluxes of calcium
and magnesium from silicate rock grains as [CO2]a falls from
1500 to 200 ppm. The feedback is regulated through the action of low
[CO2]a on host tree productivity and provides empirical
evidence for the role of [CO2]a starvation in diminishing
the contribution of trees and mycorrhizal fungi to rates of biological
weathering. More broadly, diminished tree-driven weathering under declining
[CO2]a may provide an important contributory mechanism
stabilising Earth's [CO2]a minimum over the past 24 million
years. |
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