title: Symbiotic nitrogen fixation in a tropical rainforest: 15N natural abundance measurements supported by experimental isotopic enrichment.
abstract: * Leguminous trees are very common in the tropical rainforests of Guyana. Here, species-specific differences in N(2) fixation capability among nodulating legumes growing on different soils and a possible limitation of N(2) fixation by a relatively high nitrogen (N) and low phosphorus (P) availability in the forest were investigated. * Leaves of 17 nodulating species and 17 non-nodulating reference trees were sampled and their delta(15)N values measured. Estimates of N(2) fixation rates were calculated using the (15)N natural abundance method. Pot experiments were conducted on the effect of N and P availability on N(2) fixation using the (15)N-enriched isotope dilution method. * Nine species showed estimates of > 33% leaf N derived from N(2) fixation, while the others had low or undetectable N(2) fixation rates. High N and low P availability reduced N(2) fixation substantially. * The results suggest that a high N and low P availability in the forest limit N(2) fixation. At the forest ecosystem level, N(2) fixation was estimated at c. 6% of total N uptake by the tree community. We conclude that symbiotic N(2) fixation plays an important role in maintaining high amounts of soil available N in undisturbed forest.
authors.affiliation: Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, PO Box 800.84, 3508 TB Utrecht, the Netherlands. T.L.Pons@bio.uu.nl
authors.forename: Thijs L
authors.initials: TL
authors.lastname: Pons
authors.forename: Kristel
authors.initials: K
authors.lastname: Perreijn
authors.forename: Chris
authors.initials: C
authors.lastname: van Kessel
authors.forename: Marinus J A
authors.initials: MJ
authors.lastname: Werger
mesh_terms: D017753:Ecosystem; D006172:Guyana; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D053204:Root Nodules, Plant / Q000502:physiology; D012987:Soil; D013045:Species Specificity; D013559:Symbiosis / Q000502:physiology*; D014197:Trees / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D010758:Phosphorus