title: Atmospheric CO2 enrichment alters energy assimilation, investment and allocation in Xanthium strumarium.
abstract: Energy-use efficiency and energy assimilation, investment and allocation patterns are likely to influence plant growth responses to increasing atmospheric CO2 concentration ([CO2]). Here, we describe the influence of elevated [CO2] on energetic properties as a mechanism of growth responses in Xanthium strumarium. Individuals of X. strumarium were grown at ambient or elevated [CO2] and harvested. Total biomass and energetic construction costs (CC) of leaves, stems, roots and fruits and percentage of total biomass and energy allocated to these components were determined. Photosynthetic energy-use efficiency (PEUE) was calculated as the ratio of total energy gained via photosynthetic activity (Atotal) to leaf CC. Elevated [CO2] increased leaf Atotal, but decreased CC per unit mass of leaves and roots. Consequently, X. strumarium individuals produced more leaf and root biomass at elevated [CO2] without increasing total energy investment in these structures (CCtotal). Whole-plant biomass was associated positively with PEUE. Whole-plant construction required 16.1% less energy than modeled whole-plant energy investment had CC not responded to increased [CO2]. As a physiological mechanism affecting growth, altered energetic properties could positively influence productivity of X. strumarium, and potentially other species, at elevated [CO2].
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Tennessee, 1416 Circle Drive, Knoxville, TN 37996, USA. jnagel@utk.edu
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Nagel
authors.forename: Xianzhong
authors.initials: X
authors.lastname: Wang
authors.forename: James D
authors.initials: JD
authors.lastname: Lewis
authors.forename: Howard A
authors.initials: HA
authors.lastname: Fung
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Griffin
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D018533:Biomass; D002245:Carbon Dioxide / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D005638:Fruit / Q000502:physiology; D018515:Plant Leaves / Q000502:physiology; D018517:Plant Roots / Q000502:physiology; D018547:Plant Stems / Q000502:physiology; D031210:Xanthium / Q000378:metabolism / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide