title: Contrasting arbuscular mycorrhizal responses of vascular and non-vascular plants to a simulated Palaeozoic CO₂ decline.
abstract: The arbuscular mycorrhizal (AM) fungal symbiosis is widely hypothesized to have                 promoted the evolution of land plants from rootless gametophytes to rooted                 sporophytes during the mid-Palaeozoic (480-360 Myr, ago), at a time                 coincident with a 90% fall in the atmospheric CO(2) concentration                     ([CO(2)](a)). Here we show using standardized dual isotopic                 tracers ((14)C and (33)P) that AM symbiosis efficiency                 (defined as plant P gain per unit of C invested into fungi) of liverwort                 gametophytes declines, but increases in the sporophytes of vascular plants (ferns                 and angiosperms), at 440 p.p.m. compared with 1,500 p.p.m.                     [CO(2)](a). These contrasting responses are associated with                 larger AM hyphal networks, and structural advances in vascular plant                 water-conducting systems, promoting P transport that enhances AM efficiency at 440                 p.p.m. [CO(2)](a). Our results suggest that non-vascular land                 plants not only faced intense competition for light, as vascular land floras grew                 taller in the Palaeozoic, but also markedly reduced efficiency and total capture of                 P as [CO(2)](a) fell.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, S10 2TN, UK. k.field@sheffield.ac.uk
authors.forename: Katie J
authors.initials: KJ
authors.lastname: Field
authors.forename: Duncan D
authors.initials: DD
authors.lastname: Cameron
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Leake
authors.forename: Stefanie
authors.initials: S
authors.lastname: Tille
authors.forename: Martin I
authors.initials: MI
authors.lastname: Bidartondo
authors.forename: David J
authors.initials: DJ
authors.lastname: Beerling
mesh_terms: D005075:Biological Evolution; D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism; D029624:Ferns / Q000145:classification / Q000382:microbiology* / Q000502:physiology; D005658:Fungi / Q000502:physiology*; D035926:Hepatophyta / Q000145:classification / Q000382:microbiology* / Q000502:physiology; D019684:Magnoliopsida / Q000145:classification / Q000382:microbiology* / Q000502:physiology; D038821:Mycorrhizae / Q000502:physiology*; D010163:Paleontology; D010710:Phosphates / Q000032:analysis / Q000378:metabolism; D018517:Plant Roots / Q000382:microbiology / Q000502:physiology; D012987:Soil / Q000032:analysis; D013559:Symbiosis
chemical_list: D010710:Phosphates; D012987:Soil; D002245:Carbon Dioxide