title: A trade-off between nitrogen uptake and use increases responsiveness to elevated CO2 in infrequently cut mixed C3 grasses.
abstract: The aim of this study was to evaluate whether the responsiveness of mixed C3 grass species to elevated CO2 is related more to nitrogen uptake or to N-use efficiency. Nitrogen uptake and whole-plant N-use efficiency were investigated with two binary mixtures: Lolium perenne was mixed either with Festuca arundinacea or with Holcus lanatus. The swards were grown on sand with or without CO2 doubling, and subjected to two cutting frequencies. A C20 alcohol was used as a marker to determine species proportion in the total root mass of the mixtures. The mean residence time of N was calculated from that of 15N-labelled fertilizer. Lolium perenne took up significantly more N per unit root mass than its grass competitors, but its N-use efficiency was lower. Elevated CO2 significantly reduced the N uptake of the three grass species. A trade-off between N capture and use was found, as N-use efficiency and N-uptake rate were negatively correlated. A high N-use efficiency, and conversely low N uptake appeared to favour the responsiveness to elevated CO2 of the infrequently cut grasses.
authors.affiliation: INRA, Grassland Ecosystem Research, FGEP, 234 Avenue du Brézet, F-63039 Clermont-Ferrand, France. soussana@clermont.inra.fr
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Soussana
authors.forename: Florence
authors.initials: F
authors.lastname: Teyssonneyre
authors.forename: Catherine
authors.initials: C
authors.lastname: Picon-Cochard
authors.forename: Lorna
authors.initials: L
authors.lastname: Dawson
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000502:physiology*; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen