title: Nitrogen to phosphorus ratio of plant biomass versus soil solution in a tropical pioneer tree, Ficus insipida.
abstract: It is commonly assumed that the nitrogen to phosphorus (N:P) ratio of a terrestrial plant reflects the relative availability of N and P in the soil in which the plant grows. Here, this was assessed for a tropical pioneer tree, Ficus insipida. Seedlings were grown in sand and irrigated with nutrient solutions containing N:P ratios ranging from <1 to >100. The experimental design further allowed investigation of physiological responses to N and P availability. Homeostatic control over N:P ratios was stronger in leaves than in stems or roots, suggesting that N:P ratios of stems and roots are more sensitive indicators of the relative availability of N and P at a site than N:P ratios of leaves. The leaf N:P ratio at which the largest plant dry mass and highest photosynthetic rates were achieved was approximately 11, whereas the corresponding whole-plant N:P ratio was approximately 6. Plant P concentration varied as a function of transpiration rate at constant nutrient solution P concentration, possibly due to transpiration-induced variation in the mass flow of P to root surfaces. The transpiration rate varied in response to nutrient solution N concentration, but not to nutrient solution P concentration, demonstrating nutritional control over transpiration by N but not P. Water-use efficiency varied as a function of N availability, but not as a function of P availability.
authors.affiliation: Department of Geography, McGill University, Montréal, Québec H3A-1B1, Canada.
authors.forename: Valerie
authors.initials: V
authors.lastname: Garrish
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Cernusak
authors.forename: Klaus
authors.initials: K
authors.lastname: Winter
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Turner
mesh_terms: D018533:Biomass; D030681:Ficus / Q000378:metabolism*; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots; D018547:Plant Stems / Q000378:metabolism; D012987:Soil / Q000032:analysis; D014329:Tropical Climate
chemical_list: D012987:Soil; D010758:Phosphorus; D009584:Nitrogen