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Seed dormancy and germination in an ecological context: comparative studies of annual weeds
Linköping University, Department of Physics, Chemistry and Biology, Ecology. Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [da]

Germination ecology studies, i.e. studies of interactions between characteristics of the seeds and environmental circumstances, provide understanding of spatial and temporal patterns of emergence of wild species, as weeds in the field. A large number of species have seed dormancy, i.e. seeds respond to circumstances not directly evoking germination. Thus, germination may occur only if specific environmental events have occurred in the seeds' past life story, and/or if a suitable time period has passed since ripening on mother plants. In this thesis, three characteristics, i.e. dormancy pattern, germination preferences and dormancy strength, hypothesised as mutually independent seed characteristics, are used to describe dormancy and germination in an ecological context. This conceptual model may be used for descriptions of differences between species, to understand emergence patterns in the field from controlled germination tests, and probably for increasing the understanding of evolution of ecological important properties of seed dormancy and germination.

Fifteen annual weedy taxa were investigated: two groups of temperate climate weeds, Lamium and Papaver, and one group of tropical weeds, co-occurring Asteraceae species of different genera. Intra-species variations in germination occurred for all species, but species-specific germination responses within all groups were revealed in analyses. All species showed some kind of species-specific dormancy pattern that was expressed as increased germination in response to one or more environmental factor not required for the actual germination.

For Lamium and Papaver, the general dormancy pattern was genus-specific. Germination preferences varied slightly within genus. Dormancy strength was to some extent species-specific, but highly variable. The species belonging to Asteraceae showed differences in dormancy pattern. It is shown how such differences can be visualized and compared by plotting response time and achieved germination in two-dimensional graphs, giving species-specific pictures.

Dormancy pattern and germination preferences explained how Papaver can perform as winter annuals in warmer climates, but substantially as summer annuals in colder climates, without local adaptations. For Lamium, the results indicate a local adaptation of increasing dormancy strength: in relatively cold climate in Sweden, a strong dormancy restricted a part of each cohort from germinating during autumn, thus preventing from winter mortality. For the Asteraceae, five of six species clearly responded to cold pretreatment, which is noteworthy considering the small seasonal temperature differences in the study area and in the areas of origin for the species. The six Asteraceae achieved similar emergence timing in the field by responding to different environmental factors.

Together, the results from these fifteen species indicate that dormancy pattern is an evolutionary conservative characteristic, dormancy strength is relatively easily changed, and germination preference is intermediate.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2007. , 56 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1088
Keyword [en]
Asteraceae, Bidens, Compositae, deadnettle, Galinsoga, germination timing, Guizotia, evolution, Labiatae, Lamiaceae, Lamium, morphophysiological dormancy, Papaveraceae, Papaver, Parthenium, physiological dormancy, poppy, summer annual, Tagetes, Verbesina, winter annual
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:liu:diva-11444ISBN: 978-91-85715-29-9 (print)OAI: oai:DiVA.org:liu-11444DiVA: diva2:17871
Public defence
2007-04-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:30 (English)
Opponent
Supervisors
Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2014-10-08
List of papers
1. A Comparative Study of Germination Ecology of Four Papaver Taxa
Open this publication in new window or tab >>A Comparative Study of Germination Ecology of Four Papaver Taxa
2007 (English)In: Annals of Botany, ISSN 0305-7364, E-ISSN 1095-8290, Vol. 99, no 5, 935-946 p.Article in journal (Refereed) Published
Abstract [en]

Background and Aims: Comparative studies of closely related taxa can increase understanding of adaptations and changes in seed dormancy and germination preferences in an evolutionary perspective. For such studies, a method to describe and compare the performance of taxa in a general way is needed. The germination ecology of four Papaver taxa was studied with the aim of describing and comparing their responses to different seasonal temperature regimes.

Methods: Germination of Papaver argemone, P. rhoeas, P. dubium ssp. dubium and P. dubium ssp. lecoqii was investigated in three different artificial climates over 2.5 years. Seeds were collected in southern Sweden, and samples from different populations were used as replicates of taxa.

Key Results: Despite substantial intra-taxa variation, there were clear taxon-specific responses. Most germination occurred in the warmest climate. In general, the warmer the climate the more germination occurred in autumn instead of spring. Papaver argemone, phylogenetically most distant from the others, was, in contrast to the other taxa, restricted to germinating only at lower temperatures.

Conclusions: Seed dormancy and germination may be described by dormancy pattern, germination preferences and dormancy strength. The general dormancy pattern was a common feature for these taxa and therefore probably an evolutionary conservative character. Germination preferences varied between taxa, resulting in different temperature optima and intervals for germination, and dormancy strength was to some extent taxon-specific, but highly variable. The dormancy pattern explained how the taxa can perform as winter annuals in warmer climates, but mainly as summer annuals in colder climates. Hence, there is no need to interpret the within-taxon temporal differences in seedling emergence as local adaptations. In the field, an entire seed cohort will not germinate during a single season. Instead, emergence will be distributed over several seasons, regardless of local climate, weather and soil cultivation methods.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2007
Keyword
Annual weed, germination ecology, morphophysiological dormancy, Papaver argemone, Papaver dubium, Papaver rhoeas, Papaveraceae, poppy, seed dormancy, Sweden, summer annual, winter annual
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-11884 (URN)10.1093/aob/mcm045 (DOI)
Note
The original article is: Laila M. Karlsson and Per Milberg, A Comparative Study of Germination Ecology of Four Papaver Taxa, 2007, Annals of Botany, (99), 935-946. http://dx.doi.org/10.1093/aob/mcm045.Available from: 2008-05-22 Created: 2008-05-22 Last updated: 2017-12-13
2. Seed dormancy pattern and germination preferences of the South African annual Papaver aculeatum
Open this publication in new window or tab >>Seed dormancy pattern and germination preferences of the South African annual Papaver aculeatum
2007 (English)In: South African Journal of Botany, ISSN 0254-6299, E-ISSN 1727-9321, Vol. 73, no 3, 422-428 p.Article in journal (Refereed) Published
Abstract [en]

Seeds from two populations of Papaver aculeatum, collected in South Africa, were subjected to a series of experiments to investigate their dormancy and germination. Dormancy was weak: fresh seeds germinated to nearly 100% at 20/10 and 25/15°C day/night if provided with light, up to 50% at 15/5, but not at all at 30/20°C. Warm stratification increased germination, both in darkness and at 15/5°C, but did not lead to germination at 30/20°C. Cold stratification reduced germination and limited germination to the cooler temperatures. Alternating cold and warm stratifications showed that the species undergoes dormancy cycles. When subjected to three different artificial annual changing climates, with onset both in summer and autumn, most seed germinated in the first autumn. However, in cooler climates, some germination occurred during spring and the second autumn. The general dormancy pattern; reduction during a warm period and induction during a cold, was similar to that of P. rhoeas, a European species and a wide-spread weed. However, germination temperature preferences differed by P. aculeatum avoiding germination at high temperatures, having substantially weaker dormancy when fresh and having more easily reduced dormancy, compared with P. rhoeas. These differences most likely result in differing temporal pattern of germination in the field.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2007
Keyword
Annual weed, bristle poppy, dormancy cycle, morphophysiological dormancy, Papaveraceae, thorny poppy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-11885 (URN)10.1016/j.sajb.2007.03.007 (DOI)
Note
Original publication: Laila M. Karlsson and Per Milberg, Seed dormancy pattern and germination preferences of the South African annual Papaver aculeatum, 2007, South African Journal of Botany, (73), 422-428. http://dx.doi.org/10.1016/j.sajb.2007.03.007. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2008-05-22 Created: 2008-05-22 Last updated: 2017-12-13
3. Variation within species and inter-species comparison of seed dormancy and germination of four annual Lamium species
Open this publication in new window or tab >>Variation within species and inter-species comparison of seed dormancy and germination of four annual Lamium species
2008 (English)In: Flora: Morphologie, Geobotanik, Oekophysiologie, ISSN 0367-2530, E-ISSN 1618-0585, Vol. 203, no 5, 409-420 p.Article in journal (Refereed) Published
Abstract [en]

In an ecological context, knowledge of intra-species variation in dormancy and germination is necessary both for practical and theoretical reasons. We used four or five seed batches (replicates) of four closely related annuals co-occurring in arable fields in Sweden: Lamium amplexicaule, L. confertum, L. hybridum and L. purpureum. Seeds used for experiments stemmed from plants cultivated on two sites, each site harbouring one population of each species, thereby ensuring similar environmental history of seeds. Seeds were tested for germination when fresh and after three different pre-treatments (cold or warm stratification, or dry storage) for up to 24 weeks. Seeds were also sown outdoors. Despite substantial intra-species variation, there were clear differences between species. The general seed dormancy pattern, i.e. which environmental circumstances that affect dormancy, was similar for all species; dormancy reduction occurred during warm stratification or dry storage. Even though the response to warm stratification indicate a winter annual pattern, successful plants in Sweden were mostly spring emerged. Germination in autumn occurred, but plants survived winters poorly. Consequently, as cold stratification did not reduce dormancy, strong dormancy in combination with dormancy reduction during dry periods might explain spring germination. It is hypothesized that local adaptations occur through changes mainly in dormancy strength, i.e. how much effort that is needed to reduce dormancy; strong dormancy restrict the part of each seed batch that germinate during autumn, and thus risk winter mortality, in Sweden.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2008
Keyword
Deadnettle, Lamiaceae, phenology, physiological dormancy, summer annual, winter annual
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-11806 (URN)10.1016/j.flora.2007.08.001 (DOI)
Note
Original publication: Laila M. Karlsson and Per Milberg, Variation within species and inter-species comparison of seed dormancy and germination of four annual Lamium species, 2008, Flora, (203), 5, 409-420. http://dx.doi.org/10.1016/j.flora.2007.08.001. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2008-05-22 Created: 2008-05-22 Last updated: 2017-12-13
4. Inter-species comparison of seed dormancy and germination of six annual Asteraceae weeds in an ecological context
Open this publication in new window or tab >>Inter-species comparison of seed dormancy and germination of six annual Asteraceae weeds in an ecological context
2008 (English)In: Seed Science Research, ISSN 0960-2585, E-ISSN 1475-2735, Vol. 18, 35-45 p.Article in journal (Refereed) Published
Abstract [en]

To understand germination timing in an ecological context, the response to environmental events that affect seed dormancy is central, and has to be combined with knowledge of germination responses to different circumstances. In this study, seed dormancy, germination, and emergence phenology of six annual co-occurring weedy Asteraceae species were investigated. Three pre-treatments (warm and cold stratification, and dry storage) were tested as possible dormancy affecting environmental events. Seeds were also sown outdoors. Species-specific differences were revealed in analyses. To facilitate general descriptions of dormancy patterns and germination preferences separately, condensed responses to the different possible dormancy affecting treatments and relative germination in different environments were plotted, giving species-specific patterns. Most species exhibited decreased dormancy to two or three pre-treatments. Dormancy was most effectively reduced by cold stratification for three species (Guizotia scabra, Parthenium hysterophorus, Verbesina encelioides), by warm stratification for two (Bidens pilosa, Galinsoga parviflora) and by dry storage for one (Tagetes minuta). All species germinated more when provided with light than in continuous darkness. Temperature levels most suitable for germination varied from low (15/5-20/10°C) for Verbesina encelioides to high (25/15-30/20°C) for Bidens pilosa. It is concluded that, even though the species have different dormancy patterns and germination preferences that suggest different possible distribution ranges, the species achieve similar emergence timing in the field in environments with a pronounced dry period after dispersal and small annual temperature fluctuations.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2008
Keyword
Bidens pilosa, Galinsoga parviflora, Guizotia scabra ssp. schimperi, Parthenium hysterophorus, Tagetes minuta, tropical weeds, Verbesina encelioides
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-11879 (URN)10.1017/S0960258508888496 (DOI)
Note
Original publication: Laila M. Karlsson, T. Tamado and Per Milberg, Inter-species comparison of seed dormancy and germination of six annual Asteraceae weeds in an ecological context, 2008, Seed Science Research, (18), 35-45. http://dx.doi.org/10.1017/S0960258508888496. Copyright: Cambridge University Press, http://journals.cambridge.org/Available from: 2008-05-22 Created: 2008-05-22 Last updated: 2017-12-13

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