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The Role of Fluctuating Temperatures in Germination and Establishment of Sorghum halepense. Regulation of Germination at Increasing Depths

C. M. Ghersa, R. L. Benech Arnold and M. A. Martinez-Ghersa
Functional Ecology
Vol. 6, No. 4 (1992), pp. 460-468
DOI: 10.2307/2389284
Stable URL: http://www.jstor.org/stable/2389284
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Role of Fluctuating Temperatures in Germination and Establishment of Sorghum halepense. Regulation of Germination at Increasing Depths
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Abstract

1. Field and laboratory tests explored the response of Sorghum halepense seeds to fluctuations in soil temperature, and whether that response serves as a mechanism for sensing depth and regulating seed germination. 2. Seedling production in the field was severely curtailed when seeds were planted at increasing soil depths. Soil-temperature fluctuations were strongly dependent on depth. When soil columns containing seeds were incubated at alternating temperatures of 20 and 30C, however, seed germination did not diminish with increasing depth, and an evaluation of how soil-surface shading affects the perception of depth by the seeds indicated that soil cover reduced germination of only those seeds in the upper strata of the profile. 3. These results demonstrate that sensitivity to amplitudes of temperature fluctuations in soil is a major component of the mechanism that enables S. halepense seeds to detect soil depth, but that mechanism may also include other environmental factors associated with depth. 4. In cases where after-ripening had apparently aged the seed population, the depth-detection mechanism failed, and the rate of germination was similar for seeds at different layers within the first 15 cm of the profile. This failure to regulate germination by detecting depth was related to a lower sensitivity to fluctuations in soil temperature. The existence and loss of this mechanism has possible ecological implications.

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