title: Responses of legume versus nonlegume tropical tree seedlings to elevated CO2 concentration.
abstract: We investigated responses of growth, leaf gas exchange, carbon-isotope discrimination, and whole-plant water-use efficiency (W(P)) to elevated CO(2) concentration ([CO(2)]) in seedlings of five leguminous and five nonleguminous tropical tree species. Plants were grown at CO(2) partial pressures of 40 and 70 Pa. As a group, legumes did not differ from nonlegumes in growth response to elevated [CO(2)]. The mean ratio of final plant dry mass at elevated to ambient [CO(2)] (M(E)/M(A)) was 1.32 and 1.24 for legumes and nonlegumes, respectively. However, there was large variation in M(E)/M(A) among legume species (0.92-2.35), whereas nonlegumes varied much less (1.21-1.29). Variation among legume species in M(E)/M(A) was closely correlated with their capacity for nodule formation, as expressed by nodule mass ratio, the dry mass of nodules for a given plant dry mass. W(P) increased markedly in response to elevated [CO(2)] in all species. The ratio of intercellular to ambient CO(2) partial pressures during photosynthesis remained approximately constant at ambient and elevated [CO(2)], as did carbon isotope discrimination, suggesting that W(P) should increase proportionally for a given increase in atmospheric [CO(2)]. These results suggest that tree legumes with a strong capacity for nodule formation could have a competitive advantage in tropical forests as atmospheric [CO(2)] rises and that the water-use efficiency of tropical tree species will increase under elevated [CO(2)].
authors.affiliation: Research School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia. lucas.cernusak@anu.edu.au
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Cernusak
authors.forename: Klaus
authors.initials: K
authors.lastname: Winter
authors.forename: Carlos
authors.initials: C
authors.lastname: Martínez
authors.forename: Edwin
authors.initials: E
authors.lastname: Correa
authors.forename: Jorge
authors.initials: J
authors.lastname: Aranda
authors.forename: Milton
authors.initials: M
authors.lastname: Garcia
authors.forename: Carlos
authors.initials: C
authors.lastname: Jaramillo
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Turner
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D007887:Fabaceae / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D014197:Trees / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen