title: Phosphorus availability and elevated CO2 affect biological nitrogen fixation and nutrient fluxes in a clover-dominated sward.
abstract: The response of biological nitrogen fixation (BNF) to elevated CO(2) was examined in white clover (Trifolium repens)-dominated swards under both high and low phosphorus availability. Mixed swards of clover and buffalo grass (Stenotaphrum secundatum) were grown for 15 months in 0.2 m2 sand-filled mesocosms under two CO2 treatments (ambient and twice ambient) and three nutrient treatments [no N, and either low or high P (5 or 134 kg P ha(-1)); the third nutrient treatment was supplied with high P and N (240 kg N ha(-1))]. Under ambient CO2, high P increased BNF from 410 to 900 kg ha(-1). Elevated CO2 further increased BNF to 1180 kg ha(-1) with high P, but there was no effect of CO2 on BNF with low P. Allocation of N belowground increased by approx. 50% under elevated CO2 irrespective of supplied P. The results suggest that where soil P availability is low, elevated CO2 will not increase BNF, and pasture quality could decrease because of a reduction in aboveground N.
authors.affiliation: Cooperative Research Centre for Greenhouse Accounting & Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra ACT 2601, Australia. everard.edwards@anu.edu.au
authors.forename: Everard J
authors.initials: EJ
authors.lastname: Edwards
authors.forename: Stephanie
authors.initials: S
authors.lastname: McCaffery
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
mesh_terms: D001315:Australia; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D009586:Nitrogen Fixation / Q000502:physiology*; D010758:Phosphorus / Q000378:metabolism / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism; D012987:Soil; D029921:Trifolium / Q000187:drug effects / Q000378:metabolism*
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D010758:Phosphorus