title: Increased photosynthetic acclimation in alfalfa associated with arbuscular mycorrhizal fungi (AMF) and cultivated in greenhouse under elevated CO2.
abstract: Medicago sativa L. (alfalfa) can exhibit photosynthetic down-regulation when grown in greenhouse conditions under elevated atmospheric CO2. This forage legume can establish a double symbiosis with nitrogen fixing bacteria and arbuscular mycorrhizal fungi (AMF), which may increase the carbon sink effect of roots. Our aim was to assess whether the association of alfalfa with AMF can avoid, diminish or delay the photosynthetic acclimation observed in previous studies performed with nodulated plants. The results, however, showed that mycorrhizal (M) alfalfa at the end of their vegetative period had lower carbon (C) discrimination than non-mycorrhizal (NM) controls, indicating photosynthetic acclimation under ECO2 in plants associated with AMF. Decreased C discrimination was due to the acclimation of conductance, since the amount of Rubisco and the expression of genes codifying both large and small subunits of Rubisco were similar or slightly higher in M than in NM plants. Moreover, M alfalfa accumulated a greater amount of soluble sugars in leaves than NM plants, thus favoring a down-regulation effect on photosynthetic rates. The enhanced contents of sugars in leaves coincided with a reduced percentage of arbuscules in roots, suggesting decreased sink of carbohydrates from shoots to roots in M plants. The shorter life cycle of alfalfa associated with AMF in comparison with the NM controls may also be related to the accelerated photosynthetic acclimation in M plants. Further research is needed to clarify to what extent this behavior could be extrapolated to alfalfa cultivated in the field and subjected to periodic cutting of shoots under climatic change scenarios.
authors.affiliation: Grupo de Fisiología del Estrés en Plantas (Unidad Asociada al CSIC, EEAD, Zaragoza e ICVV, Logroño), Departamento de Biología Ambiental, Facultades de Ciencias y Farmacia, Universidad de Navarra, C/ Irunlarrea, 1, 31008 Pamplona, Spain. Electronic address: niegoi@unav.es.
authors.forename: Nieves
authors.initials: N
authors.lastname: Goicoechea
authors.affiliation: Grupo de Fisiología del Estrés en Plantas (Unidad Asociada al CSIC, EEAD, Zaragoza e ICVV, Logroño), Departamento de Biología Ambiental, Facultades de Ciencias y Farmacia, Universidad de Navarra, C/ Irunlarrea, 1, 31008 Pamplona, Spain.
authors.forename: Marouane
authors.initials: M
authors.lastname: Baslam
authors.affiliation: Institute for Genomic Biology, University of Illinois at Urbana-Champaign, 1206W. Gregory Drive, Urbana, IL 61801, USA.
authors.forename: Gorka
authors.initials: G
authors.lastname: Erice
authors.affiliation: Grupo de Fisiología del Estrés en Plantas (Unidad Asociada al CSIC, EEAD, Zaragoza e ICVV, Logroño), Departamento de Biología Ambiental, Facultades de Ciencias y Farmacia, Universidad de Navarra, C/ Irunlarrea, 1, 31008 Pamplona, Spain.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Irigoyen
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D000455:Medicago sativa / Q000382:microbiology / Q000502:physiology*; D038821:Mycorrhizae / Q000378:metabolism*; D010788:Photosynthesis
chemical_list: D002245:Carbon Dioxide
keywords: Arbuscular mycorrhizal fungi (AMF); CO(2) enrichment; Medicago sativa; Photosynthesis; Rubisco