Contrasting arbuscular mycorrhizal responses ofvascular and non-vascular plants to a simulatedPalaeozoic CO_2 decline

摘要

The arbuscular mycorrhizal (Am) fungal symbiosis is widely hypothesized to have promotedthe evolution of land plants from rootless gametophytes to rooted sporophytes during themid-Palaeozoic (480–360 myr, ago), at a time coincident with a 90% fall in the atmosphericCO_2 concentration ([CO_2]a). Here we show using standardized dual isotopic tracers (14C and 33P) 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 (fernsandangiosperms), at 440p.p.m. compared with 1,500p.p.m. [CO_2]a. These contrasting responses are associated with larger Am hyphal networks, and structural advances in vascular plant waterconducting systems, promoting P transport that enhances Am efficiency at 440p.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 andtotal capture of P as [CO_2]a fell.