title: Leaf evolution: gases, genes and geochemistry.
abstract: OBJECTIVE
  This Botanical Briefing reviews how the integration of palaeontology, geochemistry and developmental biology is providing a new mechanistic framework for interpreting the 40- to 50-million-year gap between the origination of vascular land plants and the advent of large (megaphyll) leaves, a long-standing puzzle in evolutionary biology.
  
  
  METHODS
  Molecular genetics indicates that the developmental mechanisms required for leaf production in vascular plants were recruited long before the advent of large megaphylls. According to theory, this morphogenetic potential was only realized as the concentration of atmospheric CO2 declined during the late Palaeozoic. Surprisingly, plants effectively policed their own evolution since the decrease in CO2 was brought about as terrestrial floras evolved accelerating the rate of silicate rock weathering and enhancing sedimentary organic carbon burial, both of which are long-term sinks for CO2.
  
  
  CONCLUSIONS
  The recognition that plant evolution responds to and influences CO(2) over millions of years reveals the existence of an intricate web of vegetation feedbacks regulating the long-term carbon cycle. Several of these feedbacks destabilized CO2 and climate during the late Palaeozoic but appear to have quickened the pace of terrestrial plant and animal evolution at that time.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK. d.j.beerling@sheffield.ac.uk
authors.forename: David J
authors.initials: DJ
authors.lastname: Beerling
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D044822:Biodiversity; D005075:Biological Evolution; D018515:Plant Leaves / Q000235:genetics*; D010944:Plants / Q000235:genetics* / Q000378:metabolism; D012987:Soil
chemical_list: D012987:Soil