Water Use and Water Tolerance in the Riparian Species American Sycamore (Plantanus occidentalis L.) and How its Physiology Compares to the Coexisting Black Willow (Salix nigra Marshall)

Author

Eric Duncan

Date of Award

Summer 7-25-2014

Degree Type

Thesis

Degree Name

Master of Science in Integrative Biology (MSIB)

Department

Biology

First Advisor

Dr. Paula Jackson

Second Advisor

Dr. Dale Vogelien

Third Advisor

Dr. Brett McDaniel

Fourth Advisor

Dr. Mario Giraldo

Abstract

This study set out to compare aspects of water use and tolerance to inundation and drought of two riparian tree species, Platanus occidentalis L. and Salix nigra Marshall. The main goal of the study was to better understand the two species and assess the suitability of P. occidentalis for use in riparian restoration. To accomplish this, potted individuals were subjected to treatments of drought, inundation, or control, under greenhouse conditions, and separately, in order to estimate water use in trees, season-long diurnal measurements of sap flux (using Granier type thermal dissipation probes) were determined in situ for trees growing in a riparian buffer on the Kennesaw State University campus in north west Georgia. For each species, sap flux responses were examined in relation to light and vapor pressure deficit (VPD).

In order to assess each species’ response to inundation and drought, CO₂ assimilation and free leaf proline concentration were determined from greenhouse treatments, and separately for individuals growing in the field under natural conditions. Measurements of free proline concentration were also collected from greenhouse individuals to assess each species response to a spider mite infestation. Specific leaf area (m²/kg; field and greenhouse) and mean leaf area (determined as leaf area per meter of branch, m²/m; field only) were also compared. In addition, the potential propagation of P. occidentalis by stem cuttings was also explored.

Results indicated a possible difference in species water use in response to vapor pressure deficit, with S. nigra showing a stronger correlation to VPD compared to P. occidentalis. Differences among species in CO₂ assimilation were inconclusive, but species did show differences in free proline concentration in response to drought and spider mite infestation. For both (drought treatment and mite infestation) S. nigra had higher free proline values compared to P. occidentalis. Between species differences were also found for specific leaf area and average leaf area, with P. occidentalis showing higher values for both parameters.

The initial assessment of results, in combination with known morphology and life history traits suggest that P. occidentalis is a suitable, and perhaps even an advantageous addition to restoration of a riparian corridor, and thus, is recommended for use in conjunction with S. nigra in riparian buffer restoration projects.