The first objective of this study was to investigate the role of an invasive grass
species, Arundo donax (L.), on the hydrologic cycle. At a site on the Rio Grande in
South Texas, we measured the gas exchange of carbon dioxide and water vapor at the
leaf scale and structural characteristics, such as leaf area and shoot density, at the stand
scale. In order to assess the effect of water availability, this study was conducted along
transects perpendicular to the edge of the river along a potential moisture gradient. The
second objective was to quantify the effect of two herbivores, an armored scale,
Rhizaspidiotus donacis (Leonardi), and a stem-galling wasp, Tetramesa romana
(Walker),on the photosynthetic and transpiration rates of A. donax. Leaf gas exchange
measurements were made to determine the direction and magnitude of the effect on
physiological processes and by what mechanisms any effects arose.
Stands of A. donax used approximately 9.1 � 1.1 mm of water per day. This rate
of water use was at the high end of the spectrum for plants. The major controls on stand
scale transpiration were evaporative demand, leaf area index, and water availability.
During two summer seasons, stand scale transpiration varied greatly, following the pattern of variability in precipitation, suggesting that recent rainfall constituted a
significant proportion of the water taken up by this species.
Herbivory by a stem-galling wasp and a sap-feeding scale, both separately and
together, reduced the rates of leaf scale physiological processes in A. donax. The
efficacy of the wasp was density dependent, and this herbivore reduced the
carboxylation rate of Rubisco. The effect of the scale took approximately five months to
manifest, which coincided with generation time. Scale reduced photosynthesis by
decreasing the maximum rate of electron transport. When the two insects were both
present, the effect of their herbivory seemed to be additive. These results will assist the
responsible management agencies in evaluating the propriety of using one or both of the
insect herbivores as biological control agents.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-593 |
| Date | 2009 May 1900 |
| Creators | Watts, David A. |
| Contributors | Moore, Georgianne |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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