title: The role of forest trees and their mycorrhizal fungi in carbonate rock weathering and its significance for global carbon cycling.
abstract: On million-year timescales, carbonate rock weathering exerts no net effect on atmospheric CO2 concentration. However, on timescales of decades-to-centuries, it can contribute to sequestration of anthropogenic CO2 and increase land-ocean alkalinity flux, counteracting ocean acidification. Historical evidence indicates this flux is sensitive to land use change, and recent experimental evidence suggests that trees and their associated soil microbial communities are major drivers of continental mineral weathering. Here, we review key physical and chemical mechanisms by which the symbiotic mycorrhizal fungi of forest tree roots potentially enhance carbonate rock weathering. Evidence from our ongoing field study at the UK's national pinetum confirms increased weathering of carbonate rocks by a wide range of gymnosperm and angiosperm tree species that form arbuscular (AM) or ectomycorrhizal (EM) fungal partnerships. We demonstrate that calcite-containing rock grains under EM tree species weather significantly faster than those under AM trees, an effect linked to greater soil acidification by EM trees. Weathering and corresponding alkalinity export are likely to increase with rising atmospheric CO2 and associated climate change. Our analyses suggest that strategic planting of fast-growing EM angiosperm taxa on calcite- and dolomite-rich terrain might accelerate the transient sink for atmospheric CO2 and slow rates of ocean acidification.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Rachel M S
authors.initials: RM
authors.lastname: Thorley
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Lyla L
authors.initials: LL
authors.lastname: Taylor
authors.affiliation: Kroto Research Institute, University of Sheffield - North Campus, Sheffield, S3 7HQ, UK.
authors.forename: Steve A
authors.initials: SA
authors.lastname: Banwart
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Leake
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Beerling
mesh_terms: D057486:Carbon Cycle; D002254:Carbonates; D065928:Forests; D019684:Magnoliopsida; D008903:Minerals; D038821:Mycorrhizae; D012987:Soil; D014197:Trees / Q000382:microbiology* / Q000502:physiology*
chemical_list: D002254:Carbonates; D008903:Minerals; D012987:Soil
keywords: alkalinity; arbuscular mycorrhiza; chemical weathering; climate change; ectomycorrhiza; soil carbonates; soil pH