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Ecology of Capsella Bursa-Pastoris (L.) Medik. and Senecio Vulgaris L. in Relation to Germination Behaviour

A. I. Popay and E. H. Roberts
Journal of Ecology
Vol. 58, No. 1 (Mar., 1970), pp. 123-139
DOI: 10.2307/2258172
Stable URL: http://www.jstor.org/stable/2258172
Page Count: 17
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Ecology of Capsella Bursa-Pastoris (L.) Medik. and Senecio Vulgaris L. in Relation to Germination Behaviour
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Abstract

(1) An attempt has been made to relate the temporal pattern of seed germination in Senecio and Capsella to environmental conditions. This has been based on an examination of the germination of populations of seeds in the field in relation to records of environmental variables which previous laboratory investigations had shown to influence germination. (2) Most Capsella seeds show a pronounced innate dormancy which is removed by a period of cold treatment on the imbibed seeds (stratification). One winter period fulfils the requirements of most seeds, but others require two winter periods. Seasonal increases in nitrate combined with fluctuating temperatures, which can replace the stratification requirements of many seeds, may also be important in removing innate dormancy. After cold treatment the germination of most seeds will take place only if exposed to light; in other words, only if the seeds are at the soil surface. (3) Senecio seeds do not show a stratification requirement and show less initial innate dormancy than Capsella. The number of seeds showing innate dormancy varies with the season of maturation: few seeds collected in the summer show innate dormancy as compared with samples collected at other times of the year. All innate dormancy disappears after about 6 months' burial in the soil. The majority of Senecio seeds also require light for germination, though the proportion capable of germinating in the dark is greater than for Capsella, and this proportion is increased as the germination temperature is lowered to around 10° C. Consequently, it was found that initially more buried seeds of Senecio were capable of emerging than those of Capsella. (4) When buried in the soil, although innate dormancy may have disappeared, dormancy is enforced on almost the entire population of both species mainly by lack of light, though there is evidence that other factors, probably raised CO2 and lowered O2 levels, may contribute to this effect. The inhibition of germination is removed immediately if the seeds are placed in light in a normal atmosphere. (5) Germination of field populations occurs in flushes; the dates of the flushes vary from year to year but are coincident in the two species at the same sites. The first flush which usually occurs in February or March, appears to be related to the rise in soil temperature to about 10° C. Analysis of the factors causing later flushes is somewhat speculative but the results suggest that warm dry conditions followed by rain are stimulatory. An additional factor, in Capsella at least, may be high soil nitrate levels acting synergistically with large diurnal fluctuations of temperature.

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