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The effects of increasing water stress on seedlings of Sporobolus airoides (Torr.) Torr. were investigated in the laboratory under controlled growth conditions. Three groups of seedlings were germinated and grown in soil with soil moisture above field capacity for 15, 20 and 25 days. At this time watering ceased and at the end of drought periods of 5, 10, 15 and 20 days some of the seedlings were examined for total carbohydrate content, respiratory activity, and relative shoot water deficits. Other plants were rewatered after each drought period and 20 days later survival was determined visually. The dry weights of the above ground portions of these survival test plants were determined. It was found that the 20 and 25 day-old plants survived the earlier stages of drought better than the 15 day-old seedlings but this was probably due to more rapid water loss from the soil in the pots containing the 15 day-old seedlings. After extended periods of drought survival of all seedlings decreased to 10% or less. The shoots of the 25 day-old seedlings were found to retain a significantly greater amount of their tissue water. Respiratory activity increased in the 15 and 20 day-old seedlings when water was first withheld and then decreased sharply after 15 days of drought. The 25 day-old seedlings maintained a relatively constant respiratory activity at all drought periods. The carbohydrate content of the 15 and 20 day-old seedlings remained relatively constant from the initiation to the end of the drought periods with the exception of a highly significant increase for the 20 day-old seedlings at 10 days drought. The 25 day-old seedlings accumulated carbohydrates after the 5th day of drought up to the end of the drought periods. Dry weights of the shoots generally increased up through the 15th day of drought followed by significant decreases between the 15th and 20th days of drought. Results from multiple regression analysis indicate that the most reliable and most expedient criteria to use in estimating percent survival is relative shoot water deficits. It is suggested that the 25 day-old seedlings are approaching a point of physiological maturity which would enable them to survive extended periods of drought.

Project Sponsors

I would first of all like to thank Earl Aldon of the U.S. Department of Agriculture Forest and Range Experiment Station, Albuquerque, New Mexico for suggesting the problem and also for supplying the financial support which enabled me to conduct the research. I wish to thank Dr. Gordon Johnson for serving as my thesis advisor and for directing me throughout the course of study, Dr. William Martin and Dr. James Gosz for serving on my thesis committee and finally Dr. William Johnson and Dr. Jerry Traut for the moral support and an occasional helping hand. Finally I would like to dedicate this thesis in memorium to Mr. T. H. Elton Kaat for the many hours of advice he so willingly gave.



Document Type


Degree Name


Department Name

UNM Biology Department

First Committee Member (Chair)

Gordon Verle Johnson

Second Committee Member

William Clarence Martin

Third Committee Member

James Roman Gosz

Fourth Committee Member

Earl F. Aldon

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