title: Arbuscular mycorrhiza maintains nodule function during external NH4+ supply in Phaseolus vulgaris (L.).
abstract: The synergistic benefits of the dual inoculation of legumes with nodule bacteria and arbuscular mycorrhizae (AM) are well established, but the effect of an external NH(4)(+) supply on this tripartite relationship is less clear. This effect of NH(4)(+) supply was investigated with regards to the growth and function of the legume host and both symbionts. Nodulated Phaseolus vulgaris seedlings with and without AM, were grown in a sand medium with either 0 N, 1 mM or 3 mM NH(4)(+). Plants were harvested at 30 days after emergence and measurements were taken for biomass, N(2) fixation, photosynthesis, asparagine concentration, construction costs and N nutrition. The addition of NH(4)(+) led to a decline in the percentage AM colonization and nodule dry weights, although AM colonization was affected to a lesser extent. NH(4)(+) supply also resulted in a decrease in the reliance on biological nitrogen fixation (BNF); however, the AM roots maintained higher levels of NH(4)(+) uptake than their non-AM counterparts. Furthermore, the non-AM plants had a higher production of asparagine than the AM plants. The inhibitory effects of NH(4)(+) on nodule function can be reduced by the presence of AM at moderate levels of NH(4)(+) (1 mM), via improving nodule growth or relieving the asparagine-induced inhibition of BNF.
authors.affiliation: Center for Mountain Ecosystem Studies (CMES), Kunming Institute of Botany, Kunming, Yunnan 650204, China.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Mortimer
authors.forename: Maria A
authors.initials: MA
authors.lastname: Pérez-Fernández
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Valentine
mesh_terms: D005658:Fungi / Q000254:growth & development*; D038821:Mycorrhizae / Q000254:growth & development*; D027805:Phaseolus / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D010788:Photosynthesis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D053204:Root Nodules, Plant / Q000254:growth & development* / Q000378:metabolism / Q000382:microbiology
chemical_list: D000644:Quaternary Ammonium Compounds