Seed dormancy-germination variability (seed heteroblasty) Seed dormancy-germination variability (seed heteroblasty)
Common Lambsquarters (Chenopodium album) Seed Heteroblasy:
Morphology, Environment and Germination
Two publications provide insight into the germination structure of common lambsquarters seed rain arising from seed morphology and environment, with implications for the patterns of seedling recruitment.
• Seed polymorphism and germination (Williams and Harper, 1965)
•
The effects of light, temperature, after-ripening, nitrate and water on Chenopodium
album seed germination (Altenhofen, 2009)
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Seed polymorphism and germination
(Williams and Harper, 1965)
“… in C. album, not only do the dormancy breaking requirements of different seeds from one plant differ but the seed of different populations of the same species may have different requirements.”
Seed morphology
“Achenes of Chenopodium album are polymorphic; four categories can be recognized visually, brown-smooth, brown-reticulate, black-smooth and black-reticulate. All four types are borne by one plant.” “The majority of seeds borne by C. album are black and shiny but larger, light brown seeds with a mat surface are present in low proportions. Baar (1912) found that these two seed types differed in their microscopic anatomy. The testa of the black seeds is about 60 µ thick and of the brown about 16 µ. The brown are larger than the black … [brown-smooth, 1.55 mg per seed; brown-reticulate, 1.59 mg; black-smooth, 1.13 mg; black-reticulate, 1.33 mg]” “The percentage of brown seeds is fairly constant, both within and between [English] localities. In contrast, the proportion of reticulate and smooth seeds varies greatly, both between plants and between [English] populations.” “Seeds were collected from plants of C. album and the first ten seeds shed usually contained about five brown seeds, but subsequent brown seeds were shed irregularly amongst the black.”
Population morphological heterogeneity
“The testas of some seeds are smooth to striate and others bear raised lines which form reticulum [small, net-like] outlining more or less quadrate areas. Aellen (1928) used this character of the seed to define a species distinct from Chenopodium album which he named C. reticulatum. Smooth seed was regarded as diagnostic for C. album. Cole (1957), however, showed that forms bearing reticulate and smooth seeds interbreed and plants are found with both types of testa markings amongst their progeny.”
Morphology and germination
“The polymorphic seeds differ in germination requirements, responding differently to chilling and nitrate application.” “Brown seeds germinate extremely rapidly at 20° C when supplied with water … the majority of the black seeds are dormant.” “Brown seeds germinate quickly as soon as they are provided water, even at temperatures as low as 0° C. Black-reticulate seeds exhibit dormancy which is broken by nitrate but not by chilling. Black-smooth seeds show dormancy which is broken by nitrate which is partially replaceable by chilling.”
“… germination requirements:
black-reticulate: 60% do not require nitrate;
30% require nitrate
black-smooth: 30% do not require nitrate or chilling;
30% require nitrate and chilling;
30% require nitrate but not chilling …”
Ecology of common lambsquarters seed heteroblasty
“The ecological significance of seed polymorphism and the relevance of polymorphism to the interpretation of germination tests are briefly discussed.” “The three categories of seed which may be obtained from one parent differ as much in requirements for germination as many species differ from one another. In so far as germination requirements may be crucial in determining the ecology of a species, C. album produces seed with at least three different potential ecologies.” “It is doubtful whether all the variation in germination requirements of C. album has been detected by separating the four polymorphic categories. These are the only groups which can be recognized by eye, but within each category there are further behavioural differences.” “Indeed in C. album, not only do the dormancy breaking requirements of different seeds from one plant differ but the seed of different populations of the same species may have different requirements.”
“The existence of extensive variation in the seed characters between plants in the same habitat makes sampling of seed for germination tests a difficult problem – for the act of bulking the progeny from different parents is likely to mask the ecologically most interesting aspect of germination behaviour.” “… [this study] raises the interesting question of how widespread is the phenomenon of seed polymorphism in weed (and other) species.”
Conclusion
The complexity of C. album seed germination structure may provide
some insight into the complexity of recruitment patterns revealed in the research
conducted by the European Weed Research Society, Working group on germination and early
growth, on this species.
References
Aellen, P. 1928. Neue adventives Chenopodien aus Schweden. Bot. Notiser 3:203-210.
Baar, H. 1912. Zur anatomie und Keimumgsphysiologie heteromorpher Samen von Chenopodium album und Atriplex nitens. Sitzber. kais. Akad. Wiss. Wien. Math.-Naturw. 72(1):21-40.
Cole, M.J. 1957. Variation and interspecific relationships of Chenopodium album L. in Britain. Ph.D. thesis, University of Southhampton, UK.
Williams, J.T. and J.L. Harper. 1965. Seed polymorphism and germination; I. The influence of nitrates and low temperatures on the germination of Chenopodium album. Weed Research 5:141-150.