title: An evolutionary attractor model for sapwood cross section in relation to leaf area.
abstract: Sapwood cross-sectional area per unit leaf area (SA:LA) is an influential trait that plants coordinate with physical environment and with other traits. We develop theory for SA:LA and also for root surface area per leaf area (RA:LA) on the premise that plants maximizing the surplus of revenue over costs should have competitive advantage. SA:LA is predicted to increase in water-relations environments that reduce photosynthetic revenue, including low soil water potential, high water vapor pressure deficit (VPD), and low atmospheric CO(2). Because sapwood has costs, SA:LA adjustment does not completely offset difficult water relations. Where sapwood costs are large, as in tall plants, optimal SA:LA may actually decline with (say) high VPD. Large soil-to-root resistance caps the benefits that can be obtained from increasing SA:LA. Where a plant can adjust water-absorbing surface area of root per leaf area (RA:LA) as well as SA:LA, optimal RA:SA is not affected by VPD, CO(2) or plant height. If selection favours increased height more so than increased revenue-minus-cost, then height is predicted to rise substantially under improved water-relations environments such as high-CO(2) atmospheres. Evolutionary-attractor theory for SA:LA and RA:LA complements models that take whole-plant conductivity per leaf area as a parameter.
authors: Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia. mark.westoby@mq.edu.au
authors: Mark
authors: M
authors: Westoby
authors: William K
authors: WK
authors: Cornwell
authors: Daniel S
authors: DS
authors: Falster
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D004777:Environment; D019143:Evolution, Molecular; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000502:physiology; D018517:Plant Roots / Q000033:anatomy & histology / Q000378:metabolism; D018547:Plant Stems / Q000033:anatomy & histology* / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002245:Carbon Dioxide