title: Shedding light onto nutrient responses of arbuscular mycorrhizal plants: nutrient interactions may lead to unpredicted outcomes of the symbiosis.
abstract: The role and importance of arbuscular mycorrhizae (AM) in plant nitrogen (N) nutrition is uncertain. We propose that this be clarified by using more integrative experimental designs, with the use of a gradient of N supply and the quantification of an extensive array of plant nutrient contents. Using such an experimental design, we investigated AM effects on plant N nutrition, whether the mycorrhizal N response (MNR) determines the mycorrhizal growth response (MGR), and how MNR influences plants' C economy. Oryza sativa plants were inoculated with Rhizophagus irregularis or Funneliformis mossae. AM effects were studied along a gradient of N supplies. Biomass, photosynthesis, nutrient and starch contents, mycorrhizal colonization and OsPT11 gene expression were measured. C investment in fungal growth was estimated. Results showed that, in rice, MGR was dependent on AM nutrient uptake effects, namely on the synergy between N and Zn, and not on C expenditure. The supply of C to the fungus was dependent on the plant's nutrient demand, indicated by high shoot C/N or low %N. We conclude that one of the real reasons for the negative MGR of rice, Zn deficiency of AMF plants, would have remained hidden without an experimental design allowing the observation of plants' response to AM along gradients of nutrient concentrations. Adopting more integrative and comprehensive experimental approaches in mycorrhizal studies seems therefore essential if we are to achieve a true understanding of AM function, namely of the mechanisms of C/N exchange regulation in AM.
authors.affiliation: Depto. de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain; Centre for Environmental Biology, Faculty of Sciences, University of Lisbon, Lisbon, Portugal. Electronic address: ambcorrea@gmail.com.
authors.forename: Ana
authors.initials: A
authors.lastname: Corrêa
authors.affiliation: Centre for Environmental Biology, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Cruz
authors.affiliation: Depto. de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain.
authors.forename: Jacob
authors.initials: J
authors.lastname: Pérez-Tienda
authors.affiliation: Depto. de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Ferrol
mesh_terms: D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D055137:Glomeromycota / Q000502:physiology*; D038821:Mycorrhizae / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000382:microbiology* / Q000502:physiology*; D020648:Peptide Elongation Factor 1 / Q000235:genetics / Q000378:metabolism; D028061:Phosphate Transport Proteins / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013045:Species Specificity; D013559:Symbiosis / Q000502:physiology*
chemical_list: D005656:Fungal Proteins; D020648:Peptide Elongation Factor 1; D028061:Phosphate Transport Proteins; D009584:Nitrogen
keywords: Arbuscular mycorrhizae; C; Cost:benefit; Mycorrhizal growth response; N; Zn