Date of Award


Document Type


Degree Name

Master of Science (MS)


College of Science and Mathematics



Thesis Sponsor/Dissertation Chair/Project Chair

Dirk Vanderklein

Committee Member

Joshua Galster

Committee Member

Meiyin Wu


Japanese knotweed, Fallopia japónica, is an herbaceous perennial that is invasive on many continents, including North America. Stands of Japanese knotweed are often located in riparian regions, disturbed sites, and along roadways. Recent studies have evaluated the impact of Japanese knotweed on the hydrologic cycle. Japanese knotweed may have the ability to markedly decrease stream discharge, potentially because of its high LAI. In the summer of 2010, a two-part study was conducted to determine the impact of water availability on the physiology and morphology of Japanese knotweed. A greenhouse study of Japanese knotweed measured transpiration and other factors that may impact water-use, including photosynthesis, stomatal conductance, vapor pressure deficit, leaf water potential, leaf specific conductance, and instantaneous water use efficiency. Leaf and root biomass allocation was examined as well. Via a field study of Japanese knotweed growing under contrasting moisture regimes, designated dry, intermediate, and wet, LMA, node length and diameter, and stem based hydraulic conductance were compared for each moisture regime.

The greenhouse study results demonstrated that Japanese knotweed adjusted parameters to optimize use of water when available. Leaf specific hydraulic conductivity was significantly lower for drought-treated plants, at 0.20±0.01 mmol/s/m2/MPa, compared to 0.34±0.01 mmol/s/m2/MPa for watered plants (P=0.0001). Instantaneous water use efficiency increased significantly following drought treatment, with a mean of 24.22±2.05 pmol/mmol for drought-treated plants, and a mean of 17.92±1.4 pmol/mmol for the watered plants (P=0.0109). Such findings were supported by field study results. Hydraulic conductivity on a stem area basis increased significantly between wet site plants, at L16xl06±0.126xl06 mmol/s/MPa/m2, compared to 6.69x105±1.0x105 mmol/s/MPa/m2 for the intermediate site (P=0.0047) and 4.94x105±0.556xl05 mmol/s/MPa/m2 for the dry site (P=0.0001). Significant differences in LMA and internode length were also found between sites, indicating that variations in morphology may promote successful water use and transport in varied environmental conditions. Taken together, the results of these studies show that Japanese knotweed could impact water supply in invaded areas, whether dry or wet, through alterations in physiological responses and biomass allocation that allow for optimal water use under short-term and long-term moisture conditions.

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