title: Intrinsic and extrinsic hydraulic factors in varying sizes of two Amazonian palm species (Iriartea deltoidea and Mauritia flexuosa) differing in development and growing environment.
abstract: OBJECTIVE
  This study seeks to determine how hydraulic factors vary with ontogeny and whether they begin to limit further height growth in palms. Palms are an attractive group for physiological research because their columnar trunks and simple leaf habit allow key intrinsic and extrinsic hydraulic variables to be estimated more easily than in complex arborescent dicotyledons. •
  
  
  METHODS
  We measured various biometric and physiological factors including sap flux, leaf areas, turnover rates, and internode lengths in two Amazonian rainforest species: terra firme Iriartea deltoidea and swamp-adapted Mauritia flexuosa. These two palm species differ markedly in edaphic conditions, leaf type (pinnately compound vs. palmate), and bole development, making physiological comparisons between them important as well. •
  
  
  RESULTS
  The species exhibited differing patterns in height growth rate along boles, which appear to relate to their differences in bole development. Growth rates ultimately slowed at the tops of tall palms in both species. We also found a high degree of convergence in total leaf area with height in both species even though they exhibited contrasting patterns in both live frond number and leaf area per frond with height. Sap flux density from leaves was constant with height but four times greater in M. flexuosa than in I. deltoidea. •
  
  
  CONCLUSIONS
  Although height growth rates slow considerably in tall palms, neither species shows evidence that hydraulic factors become limiting because they are able to support much greater leaf areas with similar sap flux densities as shorter palms.
authors: Department of Geography and Environment, Boston University, 675 Commonwealth Ave., Boston, Massachusetts 02215 USA.
authors: Heidi J
authors: HJ
authors: Renninger
authors: Nathan
authors: N
authors: Phillips