Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Yajun Wu


abscisic acid, alfalfa, stomata, WUE


Alfalfa is an important forage crop worldwide. Being deep-rooted, N2-fixing and high yielding, alfalfa has great economic, ecological and nutritional benefits. While alfalfa is a high yielding crop, its high productivity depends on irrigation water in many areas and consumes the greatest amount of water among all the major crops. With a growing demand for water resources due to an increase in human population and industrial water use, plus frequent drought due to climate change, irrigation water has become increasingly scarce and expensive. To sustain high production of alfalfa with limited water resource, alfalfa cultivars with improved water use efficiency (WUE) is urgently needed. As a first step, we started screening alfalfa germplasms for difference in WUE and identified an alfalfa collection, River side (RS), with a greater WUE under drought compared to other ten alfalfa collections. RS is a naturalized alfalfa collected from the Grand River National Grassland in South Dakota. The objective of this study was to identify physiological and morphological traits that may contribute toward higher WUE in RS. Plants were subjected to two water regimes, by supplying either 100% (well-watered) or 50% (water-stressed) of their transpirational water needs. RS showed the smallest stomatal conductance and used the least amount of water under drought compared to other two alfalfa collections, suggesting that a greater WUE in RS is associated with a reduced transcriptional water loss. We found that RS developed smaller but more numerous stomata under drought that might facilitate a more rapid stomatal closure when water is limited but enhance water and nutrient uptake when water is sufficient. RS has also exhibited different changes on two sides of the leaf that may contribute to the regulation of water loss. The abaxial surface developed a greater number of leaf hairs that can potentially increase the boundary layer resistance for transpiration. The adaxial surface developed the stomata with a greater sensitivity to ABA. By examining the leaf epidermal cell size, it is clear that RS showed the greatest reduction in cell size, resulting in a great increase in cell density. The change in cell density may explain an increased stomatal and leaf hair density observed. Our study provided a great insight into the factors that may contribute to a high WUE in alfalfa. We hope that the knowledge developed in this study and in the future study will build a foundation for developing alfalfa with improved WUE.

Library of Congress Subject Headings

Alfalfa -- Water requirements.
Alfalfa -- Irrigation.
Alfalfa -- Drought tolerance.
Plants -- Transpiration.
Plant physiology.


Includes bibliographical references (pages 49-57)



Number of Pages



South Dakota State University



Rights Statement

In Copyright