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Open Access Thesis

Keywords

Desert plants--Mexico--Chihuahua (Chihuahua); Cruciferae; Desert plants; Germination; Mexico--Chihuahua (Chihuahua);

Abstract

Seeds of Lepidium lasiocarpum Nutt., Lepidium medium Greene var. medium, and Descurainea pinnata (Walt.) Britton ssp. ochroleuca (Woot.) Detling, native to the Chihuahuan Desert, were tested for their germination responses under conditions of constant and fluctuating temperatures, light and dark sensitivity, and different seed depths in soil. The effects of a three day drying period alternating with one day of moisture at field capacity was also investigated. All three species germinated optimally under fluctuating temperatures with low temperatures near 5-10°c and high temperatures near 20-25°C. L. lasiocarpum seeds responded better to fluctuating temperatures of 15°c magnitude than to fluctuations of 5, 10, or 20°c . L. medium and D. pinnata responded best to fluctuating temperatures of 10 or 15°c magnitude. Time of germination responses after the seeds were moistened differed between the constant and fluctuating temperature tests. Seeds under constant temperatures and light germinated after 1-2 days of exposure whereas seeds under constant temperatures and dark took 4-5 days to respond. Germination occurred after 3-4 days in both light and dark tests under fluctuating temperatures. Fluctuating temperatures negate the effect of light; therefore, fluctuating temperatures are more important in the regulation of germination of these species than is light. Germination tests at 5 soil depths under favorable temperatures indicated that germination of the three species of this study takes place at depths less than 6 mm. The depth of optimal emergence for L. medium and L. lasiocarpum was 4 mm. D. pinnata seeds which germinated at 2 mm or deeper did not emerge. Measurements of light penetration into the soil suggested a correlation between depth of germination and light penetration. Germination tests using alternating moisture levels under optimal temperatures demonstrated that soil moisture at or near field capacity is a primary control of germination. No germination occurred for seeds of L. medium and D. pinnata. Whereas L. lasiocarpum seeds germinated (18 percent) only at 2 mm with 6 percent emergence. Within the study site, the species of this study were noted to occur in zones distinct from one another. The physical factors investigated did not appear to be directly responsible for this zonation. However, it is suggested that the physical factors of this study could be indirectly responsible as the result of different soil types corresponding with the different zones of plants. In this study the results have suggested that soil moisture at or near field capacity in combination with favorable fluctuating temperatures and appropriate soil depths are the primary determining factors of germination of the three crucifers studied. These requirements are specific and limit mass germination to cool, rainy seasons when seedling survival is high.

Year of Submission

1975

Degree Name

Master of Arts

Department

Department of Biology

First Advisor

Daryl D. Smith

Second Advisor

Erwin Richter

Third Advisor

Robert J. Simpson

Comments

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Date Original

1975

Object Description

1 PDF file (54 leaves)

Language

en

File Format

application/pdf

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