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A Comparative Study of Germination Characteristics in a Local Flora

J. P. Grime, G. Mason, A. V. Curtis, J. Rodman and S. R. Band
Journal of Ecology
Vol. 69, No. 3 (Nov., 1981), pp. 1017-1059
DOI: 10.2307/2259651
Stable URL: http://www.jstor.org/stable/2259651
Page Count: 43
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A Comparative Study of Germination Characteristics in a Local Flora
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Abstract

(1) Using a standardized procedure, a laboratory study was made of the germination characteristics of seeds collected from a wide range of habitats in the Sheffield region. Measurements were conducted on freshly-collected seeds and on samples subjected to dry storage, chilling and scarification. Responses to temperature and light flux were also examined. (2) The data have been used to compare the germination biology of groups of species classified with respect to various criteria including life-form, family, geographical distribution, ecology, and seed shape, weight and colour. (3) Marked differences were observed in the capacity of freshly-collected seeds for immediate germination. Of the 403 species examined, 158 failed to exceed 10% germination but 128 attained values greater than 80%. Germination was high in the majority of grasses and low in many annual forbs and woody species. With respect to initial germinability, major families could be arranged in the series Gramineae > Compositae > Leguminosae = Cyperaceae > Umbelliferae. Many small-seeded species were able to germinate immediately after collection and seeds of these species were often elongated or conical and had antrorse hairs or teeth on the dispersule. High initial germinability was conspicuous among the species of greatest abundance in the Sheffield flora. (4) In the majority of species, germination percentage increased during dry storage; this effect was most marked in small-seeded species. Among the seventy-five species which responded to chilling, some germinated at low temperature in darkness whilst others were dependent upon subsequent exposure to light or to higher temperature or to both. Responses to chilling were characteristic of the Umbelliferae. In all of the legumes examined, rapid germination to a high percentage was brought about by scarification. (5) Under the experimental conditions, all of the annual grasses showed the potential for rapid germination. High rates were also observed in many of the annual forbs and perennial grasses. Low rates of germination occurred in the majority of sedges, shrubs and trees, and were particularly common in species of northern distribution in Britain. Rapid germination was characteristic of the species of greatest abundance in the Sheffield flora. Rate of germination showed a progressive decline with increasing seed weight, and, with some exceptions, there was a positive correlation between rate of germination and the relative growth rate of the seedling. (6) In sixteen species, germination in the light was found to be dependent upon exposure to diurnal fluctuations in temperature. Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles. A requirement for relatively high temperature was apparent in sedges, in plants of northern distribution and in a majority of the marsh plants. The range of constant temperatures conducive to germination tended to be wider in grassland plants than in woodland species. Rapid germination over a wide range of temperature occurred in many of the species which attain greatest abundance in the Sheffield flora. (7) Although germination in most species was promoted by light, some were inhibited under relatively high light flux. In 104 species a marked reduction in germination occurred if seeds were kept in the dark, and in many species this inhibitory effect could be intensified by either or both excluding temperature fluctuations and abandoning the use of a green `safety' light. The capacity for germination in darkness was observed in all of the legumes and many of the grasses. Dark germination did not occur in the Cyperaceae and was uncommon in the Compositae. The inhibitory effect of darkness was characteristic of many of the species known to form reserves of buried seeds, but it occurred also in certain species with more transient seed banks. (8) There were recurrent associations between features of seed morphology and of germination, several of which coincided with particular ecological characteristics. (9) The functional significance of some of the germination characteristics observed in this study leads us to the conclusion that certain regenerative mechanisms in the field may be predicted from the laboratory characteristics of the seed.

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