Limits...
Ectomycorrhizal fungi and past high CO2 atmospheres enhance mineral weathering through increased below-ground carbon-energy fluxes.

Quirk J, Andrews MY, Leake JR, Banwart SA, Beerling DJ - Biol. Lett. (2014)

Bottom Line: Trees were grown in either a simulated past CO2 atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2 (450 ppm).Calcium dissolution rates halved for both AM and EM trees as CO2 fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2 approached rates for EM trees at near-current CO2.Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2 over millions of years.

View Article: PubMed Central - PubMed

ABSTRACT
Field studies indicate an intensification of mineral weathering with advancement from arbuscular mycorrhizal (AM) to later-evolving ectomycorrhizal (EM) fungal partners of gymnosperm and angiosperm trees. We test the hypothesis that this intensification is driven by increasing photosynthate carbon allocation to mycorrhizal mycelial networks using 14CO2-tracer experiments with representative tree–fungus mycorrhizal partnerships. Trees were grown in either a simulated past CO2 atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2 (450 ppm). We report a direct linkage between photosynthate-energy fluxes from trees to EM and AM mycorrhizal mycelium and rates of calcium silicate weathering. Calcium dissolution rates halved for both AM and EM trees as CO2 fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2 approached rates for EM trees at near-current CO2. Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2 over millions of years.

Show MeSH
Weathering reactors with representative trees of (a) G. biloba (AM), (b) S. sempervirens (AM), (c) M. grandiflora (AM), (d) P. sylvestris (EM) and (e) B. pendula (EM) (scale bar, 100 mm). (f) Typical AM fungal colonization of Ginkgo roots and (g) EM hyphal tips and associated mycelium of Pinus roots from our experiments (scale bars, 1 mm). (h,i) Hyphal interactions with basalt grains in mesh cores (scale bars, 0.1 mm). (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4126629&req=5

RSBL20140375F1: Weathering reactors with representative trees of (a) G. biloba (AM), (b) S. sempervirens (AM), (c) M. grandiflora (AM), (d) P. sylvestris (EM) and (e) B. pendula (EM) (scale bar, 100 mm). (f) Typical AM fungal colonization of Ginkgo roots and (g) EM hyphal tips and associated mycelium of Pinus roots from our experiments (scale bars, 1 mm). (h,i) Hyphal interactions with basalt grains in mesh cores (scale bars, 0.1 mm). (Online version in colour.)

Mentions: Guided by time-constrained molecular phylogenies [13,14], we selected mycorrhizal host trees that represent exemplar taxa of past forests. These included early AM gymnosperm hosts Ginkgo biloba and Sequoia sempervirens and the early AM angiosperm host Magnolia grandiflora (figure 1). The responses of these AM partnerships were compared with Pinus sylvestris (EM gymnosperm) and Betula pendula (EM angiosperm), which have stem-group ages dating to the Cretaceous. We quantified carbon flows into mycorrhizal networks using standardized methodology involving 14CO2 tracers, and measured corresponding rates of calcium dissolution from basalt colonized by mycorrhizal mycelium as the most important silicate rock for global geochemical carbon cycling.Figure 1.


Ectomycorrhizal fungi and past high CO2 atmospheres enhance mineral weathering through increased below-ground carbon-energy fluxes.

Quirk J, Andrews MY, Leake JR, Banwart SA, Beerling DJ - Biol. Lett. (2014)

Weathering reactors with representative trees of (a) G. biloba (AM), (b) S. sempervirens (AM), (c) M. grandiflora (AM), (d) P. sylvestris (EM) and (e) B. pendula (EM) (scale bar, 100 mm). (f) Typical AM fungal colonization of Ginkgo roots and (g) EM hyphal tips and associated mycelium of Pinus roots from our experiments (scale bars, 1 mm). (h,i) Hyphal interactions with basalt grains in mesh cores (scale bars, 0.1 mm). (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126629&req=5

RSBL20140375F1: Weathering reactors with representative trees of (a) G. biloba (AM), (b) S. sempervirens (AM), (c) M. grandiflora (AM), (d) P. sylvestris (EM) and (e) B. pendula (EM) (scale bar, 100 mm). (f) Typical AM fungal colonization of Ginkgo roots and (g) EM hyphal tips and associated mycelium of Pinus roots from our experiments (scale bars, 1 mm). (h,i) Hyphal interactions with basalt grains in mesh cores (scale bars, 0.1 mm). (Online version in colour.)
Mentions: Guided by time-constrained molecular phylogenies [13,14], we selected mycorrhizal host trees that represent exemplar taxa of past forests. These included early AM gymnosperm hosts Ginkgo biloba and Sequoia sempervirens and the early AM angiosperm host Magnolia grandiflora (figure 1). The responses of these AM partnerships were compared with Pinus sylvestris (EM gymnosperm) and Betula pendula (EM angiosperm), which have stem-group ages dating to the Cretaceous. We quantified carbon flows into mycorrhizal networks using standardized methodology involving 14CO2 tracers, and measured corresponding rates of calcium dissolution from basalt colonized by mycorrhizal mycelium as the most important silicate rock for global geochemical carbon cycling.Figure 1.

Bottom Line: Trees were grown in either a simulated past CO2 atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2 (450 ppm).Calcium dissolution rates halved for both AM and EM trees as CO2 fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2 approached rates for EM trees at near-current CO2.Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2 over millions of years.

View Article: PubMed Central - PubMed

ABSTRACT
Field studies indicate an intensification of mineral weathering with advancement from arbuscular mycorrhizal (AM) to later-evolving ectomycorrhizal (EM) fungal partners of gymnosperm and angiosperm trees. We test the hypothesis that this intensification is driven by increasing photosynthate carbon allocation to mycorrhizal mycelial networks using 14CO2-tracer experiments with representative tree–fungus mycorrhizal partnerships. Trees were grown in either a simulated past CO2 atmosphere (1500 ppm)—under which EM fungi evolved—or near-current CO2 (450 ppm). We report a direct linkage between photosynthate-energy fluxes from trees to EM and AM mycorrhizal mycelium and rates of calcium silicate weathering. Calcium dissolution rates halved for both AM and EM trees as CO2 fell from 1500 to 450 ppm, but silicate weathering by AM trees at high CO2 approached rates for EM trees at near-current CO2. Our findings provide mechanistic insights into the involvement of EM-associating forest trees in strengthening biological feedbacks on the geochemical carbon cycle that regulate atmospheric CO2 over millions of years.

Show MeSH