Master's Theses

Department

Biology

Degree Name

Master of Science (MS)

Abstract

The introduced shrub Tamarix ramosissima Lebed. invades riparian zones, but loses competitiveness under flooding. This was tested in Tamarix ramosissima by examining responses to flooding by soil type in a greenhouse setting. A field study examined responses of Tamarix ramosissima and other species to natural flooding. Leaf level photosynthesis rates, stomatal conductance, transpiration, and root alcohol dehydrogenase (ADH) activity were measured weekly to assess oxygen stress. In the field, stomatal conductance, leaf water potential, transpiration, canopy cover, and δ13C were measured as responses to soil water potential, soil moisture, Julian date, relative humidity, and water depth. In the greenhouse study, flooding affected Tamarix ramosissima initially. Photosynthesis rates within flooded plants ranged from 7.5 to 14 μmol CO2 m-2 s-1 during the first two weeks, but increased to 26.9 to 27 μmol CO2 m-2 s-1 by the fourth week. As flooding progressed, photosynthesis rates increased as plants became acclimated. Lower photosynthesis rates at the onset of flooding could account for the susceptibility of Tamarix ramosissima to flooding. Soil type had no effect on photosynthesis rates or on root ADH activity. Root ADH activity was higher in flooded plants compared to drained plants, indicating oxygen stress in flooded plants. The ability of Tamarix ramosissima to acclimate to flooding within four weeks indicated metabolic acclimation. In the field study, Tamarix ramosissima had lower stomatal conductance and leaf water potential compared to Populus deltoides Bartr. and Phragmites australis (Cav.) Trin. ex Steud at -1.4 MPa and 1.5 mol H2O m-2 s-1. Lower leaf water potential and stomatal conductance in the field can also account for loss of competitiveness of Tamarix ramosissima under flooding. Typha angustifolia L. had the highest canopy cover compared to Tamarix ramosissima, Melilotus officinalis (L.) Lam., Baccharis salicina Torr. & A. Gray, and Saccharum ravennae (L.) L. Differences in canopy cover indicated Typha angustifolia was more tolerant of flooding compared to Tamarix ramosissima. Nonetheless, T. ramosissima is more flooding tolerant than previously realized. Differences in physiological responses for Tamarix ramosissima could become important for ecological or management concerns with this species.

Keywords

Tamarix ramosissima Lebed., flooding, root alcohol dehydrogenase, photosynthesis, δ13C, plant water potential, canopy cover

Advisor

Dr. Brian Maricle

Date of Award

Fall 2010

Document Type

Thesis

Rights

© The Author(s)

Comments

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