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
Photosynthate allocation through mycorrhizal mycelium to basalt and rates of silicate-bound calcium dissolution over the duration of the study for each tree species (a,c), and each mycorrhizal type (b,d) at each [CO2]a. Cross-plots of carbon allocation and silicate-bound calcium dissolution for (e) each species: AM Ginkgo (circles), AM Sequoia (triangles), AM Magnolia (squares), EM Pinus (inverted triangles) and EM Betula (diamond); and (f) mycorrhizal type (circles are AM and squares are EM). Open symbols represent 450 ppm, filled symbols represent 1500 ppm [CO2]a. All values show mean ± s.e.m. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSBL20140375F2: Photosynthate allocation through mycorrhizal mycelium to basalt and rates of silicate-bound calcium dissolution over the duration of the study for each tree species (a,c), and each mycorrhizal type (b,d) at each [CO2]a. Cross-plots of carbon allocation and silicate-bound calcium dissolution for (e) each species: AM Ginkgo (circles), AM Sequoia (triangles), AM Magnolia (squares), EM Pinus (inverted triangles) and EM Betula (diamond); and (f) mycorrhizal type (circles are AM and squares are EM). Open symbols represent 450 ppm, filled symbols represent 1500 ppm [CO2]a. All values show mean ± s.e.m. (Online version in colour.)

Mentions: Our experiments show that both the advance from AM to EM mycorrhizal functional types and high atmospheric [CO2]a increase carbon fluxes into mycorrhizal mycelium and drive enhanced silicate weathering (figure 2). At high [CO2]a, photosynthate allocation to mycorrhizal mycelium colonizing basalt was 2–7 times greater for EM Pinus and Betula than for the AM trees (figure 2a,b) (F4,27 = 3.84; p = 0.014). Moreover, this photosynthate allocation via EM mycelium doubled at 1500 ppm compared with that at 450 ppm [CO2]a (figure 2b) (F1,10 = 9.07; p = 0.013). For AM trees, carbon allocation to mycorrhizal fungi varied greatly between species and generally doubled at 1500 ppm [CO2]a, but this was not significant (figure 2a,b) (F1,18 = 0.01; p = 0.920). Stimulation of carbon-energy flows into EM mycelium by high [CO2]a is independently supported by previous studies of mycorrhizal P. sylvestris seedlings grown at 700 ppm versus 350 ppm [CO2]a in which exudation of low molecular weight organic compounds, implicated in mineral weathering, increased by up to 270% [15].Figure 2.


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)

Photosynthate allocation through mycorrhizal mycelium to basalt and rates of silicate-bound calcium dissolution over the duration of the study for each tree species (a,c), and each mycorrhizal type (b,d) at each [CO2]a. Cross-plots of carbon allocation and silicate-bound calcium dissolution for (e) each species: AM Ginkgo (circles), AM Sequoia (triangles), AM Magnolia (squares), EM Pinus (inverted triangles) and EM Betula (diamond); and (f) mycorrhizal type (circles are AM and squares are EM). Open symbols represent 450 ppm, filled symbols represent 1500 ppm [CO2]a. All values show mean ± s.e.m. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSBL20140375F2: Photosynthate allocation through mycorrhizal mycelium to basalt and rates of silicate-bound calcium dissolution over the duration of the study for each tree species (a,c), and each mycorrhizal type (b,d) at each [CO2]a. Cross-plots of carbon allocation and silicate-bound calcium dissolution for (e) each species: AM Ginkgo (circles), AM Sequoia (triangles), AM Magnolia (squares), EM Pinus (inverted triangles) and EM Betula (diamond); and (f) mycorrhizal type (circles are AM and squares are EM). Open symbols represent 450 ppm, filled symbols represent 1500 ppm [CO2]a. All values show mean ± s.e.m. (Online version in colour.)
Mentions: Our experiments show that both the advance from AM to EM mycorrhizal functional types and high atmospheric [CO2]a increase carbon fluxes into mycorrhizal mycelium and drive enhanced silicate weathering (figure 2). At high [CO2]a, photosynthate allocation to mycorrhizal mycelium colonizing basalt was 2–7 times greater for EM Pinus and Betula than for the AM trees (figure 2a,b) (F4,27 = 3.84; p = 0.014). Moreover, this photosynthate allocation via EM mycelium doubled at 1500 ppm compared with that at 450 ppm [CO2]a (figure 2b) (F1,10 = 9.07; p = 0.013). For AM trees, carbon allocation to mycorrhizal fungi varied greatly between species and generally doubled at 1500 ppm [CO2]a, but this was not significant (figure 2a,b) (F1,18 = 0.01; p = 0.920). Stimulation of carbon-energy flows into EM mycelium by high [CO2]a is independently supported by previous studies of mycorrhizal P. sylvestris seedlings grown at 700 ppm versus 350 ppm [CO2]a in which exudation of low molecular weight organic compounds, implicated in mineral weathering, increased by up to 270% [15].Figure 2.

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