Abstract Detail

Watertransport in plants at multiple scales: A physiological, ecological, andevolutionary appraisal

North, Gretchen [1], Phillips, Carly [2], Woodside, Walter [2].

Tank Bromeliads: Leaf Hydraulic Conductance Is All There Is.

Tank bromeliads are intriguing case studies for plant hydraulics because they lack stems and absorptive roots. Essentially, for them, leaf hydraulic conductance is plant hydraulic conductance. Tank bromeliads also provide excellent models in which to investigate external and internal regulators of leaf hydraulic conductance because light exposure and pH, which are known to affect leaf hydraulic conductance at least in part via their effects on aquaporins, can vary widely, even within a single species. For four species of tank bromeliad that occur at La Selva Biological Station in Costa Rica, we measured light availability, the pH of tank water, and several leaf properties associated with hydraulic conductance. Plants were collected from tree falls and from different heights within the canopy, ranging from deep shade to near full exposure, and the pH of tank contents was measured for plants in situ. The first hypothesis tested was that increasing exposure to light would increase leaf hydraulic conductance (k_leaf), as estimated based on tracheid diameters and number and placement of vascular bundles determined from leaf cross-sections and leaf clearings. The second hypothesis was that light would influence the pH of tank water, which would in turn influence water uptake by the leaves, because a pH lower than 4.0 (as frequently occurs for tank bromeliads in the field) has been associated with aquaporin closure in roots and leaves of other species. The first hypothesis was supported in that k_leaf was significantly higher for plants growing higher in the canopy than for plants from lower levels and lower light exposures for the CAM species Aechmea nudicaulis and the CAM intermediate, Guzmania monostachia. Similarly, k_leaf was higher for the C3 species Werauhia gladioflora growing in high light than for W. ringens growing in full shade. With respect to the second hypothesis, the pH of tank water in the field tended to be lower for plants in higher light, and was significantly lower for plants of A. nudicaulis grown in a growth chamber under high light than under low light (pH of 4.5 vs. 5.8 at PAR of 350 vs. 50 µmol m^-2 s^-1,respectively; P = 0.018). Manipulations of tank water pH using a variety of acids indicated no clear relationship between pH and water uptake, perhaps due to buffering activity by epidermal trichomes.Thus, a low tank pH would not necessarily counteract the effect of high light on k_leaf for tank bromeliads.

Broader Impacts:

1 - Occidental College, 1600 CAMPUS RD, LOS ANGELES, CA, 90041, USA
2 - Occidental College, Biology, 1600 Campus Rd, Los Angeles, CA, 90041, USA

Keywords:
epiphyte
tracheid
Neotropics.

Presentation Type: Symposium or Colloquium Presentation
Session: SY03
Location: Delaware C/Hyatt
Date: Monday, July 9th, 2012
Time: 4:30 PM
Number: SY03008
Abstract ID:931