title: The presence of nodules on legume root systems can alter phenotypic plasticity in response to internal nitrogen independent of nitrogen fixation.
abstract: All higher plants show developmental plasticity in response to the availability of nitrogen (N) in the soil. In legumes, N starvation causes the formation of root nodules, where symbiotic rhizobacteria fix atmospheric N2 for the host in exchange for fixed carbon (C) from the shoot. Here, we tested whether plastic responses to internal [N] of legumes are altered by their symbionts. Glasshouse experiments compared root phenotypes of three legumes, Medicago truncatula, Medicago sativa and Trifolium subterraneum, inoculated with their compatible symbiont partners and grown under four nitrate levels. In addition, six strains of rhizobia, differing in their ability to fix N2 in M. truncatula, were compared to test if plastic responses to internal [N] were dependent on the rhizobia or N2 -fixing capability of the nodules. We found that the presence of rhizobia affected phenotypic plasticity of the legumes to internal [N], particularly in root length and root mass ratio (RMR), in a plant species-dependent way. While root length responses of M. truncatula to internal [N] were dependent on the ability of rhizobial symbionts to fix N2 , RMR response to internal [N] was dependent only on initiation of nodules, irrespective of N2 -fixing ability of the rhizobia strains.
authors.affiliation: Division of Plant Science, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Chooi-Hua
authors.initials: CH
authors.lastname: Goh
authors.affiliation: Division of Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Adrienne B
authors.initials: AB
authors.lastname: Nicotra
authors.affiliation: Division of Plant Science, Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Mathesius
mesh_terms: D046913:Medicago truncatula / Q000033:anatomy & histology* / Q000187:drug effects / Q000382:microbiology; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000494:pharmacology*; D009586:Nitrogen Fixation / Q000187:drug effects*; D009929:Organ Size / Q000187:drug effects; D010641:Phenotype; D055170:Plant Root Nodulation / Q000187:drug effects; D012231:Rhizobium / Q000187:drug effects / Q000502:physiology; D053204:Root Nodules, Plant / Q000033:anatomy & histology* / Q000187:drug effects / Q000382:microbiology; D013045:Species Specificity; D029921:Trifolium / Q000033:anatomy & histology* / Q000187:drug effects / Q000382:microbiology
chemical_list: D009566:Nitrates; D009584:Nitrogen
keywords: Lateral root; Medicago sativa (L.); Medicago truncatula (Gaertn.); Trifolium subterraneum (L.); nitrogen; nodule; phenotypic plasticity; rhizobia; root architecture