Renninger, Heidi , Phillips, Nathan .
Hydraulic limitation to increased height growth of tall palms in Amazonia.
As trees grow taller, the cost of moving water to their leaves becomes higher and could begin to limit carbon gain and subsequent growth. Thus, the hydraulic limitation hypothesis states that as trees grow taller, the path length and therefore frictional resistance of water flow increases, leading to stomatal closure, reduced photosynthesis and decreased height growth in tall trees. Although this hypothesis is supported by the physical laws of water movement in trees, its validation has been complicated by the complex structure of most tree species. Their complex branching patterns make determination of whole tree path length, leaf area and stomatal conductance very difficult. Therefore, this study seeks to test the hydraulic limitation hypothesis in palms, a group of organisms that while growing to very tall heights, are still structurally simple enough to provide a model organism to test the hydraulic limitation hypothesis. Sapflux was measured using heat-dissipation sensors in Mauritia flexuosa, a species that typically grows in palm swamps, and Iriartea deltoidea, a species that typically grows on terra firma. Leaf area and bole area were also estimated and stomatal conductance per unit leaf area was calculated. Neither species showed evidence of stomatal closure in tall palms. However, unlike I. deltoidea, tall M. flexuosa palms had lower leaf area/bole area ratios than shorter trees. Likewise, when calculations of stomatal conductance were performed with all M. flexuosa palms having an average leaf area/bole area ratio, the tallest palms exhibited decreased stomatal conductance relative to the shorter individuals. Therefore, tall M. flexuosa palms appear to show signs of hydraulic limitation while I. deltoidea palms do not. This may be the result of structural differences between the two species with tall I. deltoidea palms possibly having deeper roots and a greater water storage capacity relative to shorter trees than M. flexuosa.
Log in to add this item to your schedule
1 - Boston University, Geography and Environment, 675 Commonwealth Ave, Boston, Ma, 02215, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Stevens 1/Hilton
Date: Tuesday, July 10th, 2007
Time: 10:30 AM