Lecture 3: Ecology of Seed Germination Flashcards
Highbush cranberry
Viburnum opulus
- attracts Cedar Waxwings
Seed Disperal: Fruits
- attracts organisms to move seeds for them
- often attract frugivores
- asynchronous fruiting - plants tend to do this in the wild, all fruits don’t ripen at the same time, and dispersed seeds will be different age groups and success increases -> this enhances overall survival
- toxic fruits
Fruit
ripened ovary
What type of fruiting don’t humans want?
Humans don’t want asynchronous fruiting so they can collect fruits all at one time
Other dispersal mechanisms
- wind - surface area of seed to help seed dispersal
- animals: frugivores (those specializing in fruit) & granivores (those specializing in seeds)
- water
water
- ethanobotany ( how humans use plants) - when trying to discover where they come from, seeds dispersed via water, can be hard to track
Elaiosomes on Sanguinaria canadensis
- sticky/sweet coating
- nutrient rich reward for seed dispersal animal
- favored by ants
- Blood root (Sanguinaria canadensis)
Frequency distribution of seeds dispersed over given distance classes - seed dispersal kernel
- what these graphs show
- overall there are fewer seeds dispersed far away from the parents
- mammals are the most important for carrying the seeds long distances from parent
Seed Bank: Temporal dispersal
- pool of buried seeds (definition of seed bank) - stored underground
- ‘Memory’ of the site - things will grow that were not known to be there
- long-lived seeds in seed bank, but short-lived plants - do well in disturbed environment
Prunus pennsylvanica
Pin cherry
- Pin cherry seeds were dormant in the seed bank, and grew when forest was clear-cut - it wasn’t present in this area until it was clear-cut
- it resided in the seed bank and has some longevity in there
William J. Beale’s jar experiments
- He wanted to know how long seeds lasted
- 20 jars
- 50 seeds of 19 species
- examined viability every 5-10 years -> grew a portion of the seeds out - if grew then seed was viable; if not then death in seed bank
- 120 yr. old (Malva pusilla) and (Verbascum spp.) seeds remained viable
- bet hedging - purpose for the seed - if seed can last long in seed bank, then it can wait until favorable conditions -> ensures seeds will be successful when plants disperse them -> basically so the seed can pick the best time to germinate
bet hedging
- purpose for the seed
- if seed can last long in seed bank then it can wait until favorable conditions to germinate
- ensures seeds will be successful when plants disperse them
Seed dormancy (I think in relation to Beale’s experiment?)
- buried seed of “Verbascum thapsiforme” survived 850 yrs. of dormancy
- dormant seeds produced in large numbers by populations subject to periodical local extinction
- sometimes local extinctions of a gene pool of seeds but they may also exist somewhere else because of dispersal
Why do habitats with frequent disturbance also promote genetic variability?
- frequent recruitment from gene pool - seed bank
- disturbance reduces plant-plant competition
- genetic variability of seed bank if seeds are long-lived
- areas with frequent disturbance pull from the seed bank periodically, which increases genetic diversity
Seed bank and genetic diversity:
Linanthus parryae of Mojave Desert
- seed banks of mixed genetic origins
- emerging cohorts draw from seeds originating at different times
- ratio of purple to white flowers determined by spatially variable natural selection
- used color as a substitute for genomes to see the forms of natural selection
- seed pool buffers genetic changes in plant populations
Germination timing:
see graph handout!
- seedlings that emerge earlier (correlate with earlier germination) tend to have higher survival rates
- research question: order of emergence more important than date of emergence
- research question: deteriorating environmental condition OR older plants capture more resources
Seed size tradeoffs:
Why don’t they all have big seeds?
- graph on left shows that bigger seeds have lower death rates - have better chance of producing a seedling that survives
- graph on right shows the energy allocated between growth and reproduction - trade-offs in creating seeds with growth
- energy costs - trade offs -> large seeds might be produced in late-successional situations, whereas several smaller seeds might be more cost effective in situations with high disturbance, shorter plant life, etc.
- dispersal ability
- ability to produce more seeds
Microtopographical Variation
- variation in soil conditions/topographical features
Safe sites
- the lab is not the field
- seed germination responsive to fine-scale differences in physical environment
- nurse logs
- flat seeds of Achillea millefolium germinate best on even surface
- Prunella vulgaris prefers 20 mm grooves
nurse log
- important sites for germination especially in forested situations, mature forests, late-succesional forests, temperate, and tropical forests
- some smaller seeds will grow on logs because there is not litter accumulation there- this occurs a lot in places with a lot of leaf litter
- i.e. small seeds like birch and hemlock can get buried sometimes in leaf litter
- i.e. a trees root system growing over a large log
- i.e. tree roots growing over large log
seed “sinks”
- seeds that don’t remain in seed bank
Why do only a tiny fraction of seeds reach the seedling phase?
- predation; digested to the point where seed is no longer viable
Summary - factors affecting germination
- species composition of seed bank
- seed looses in the field
- physical characteristics of seed bed
- physical characteristics of seeds
- Physiological Cues:
- light intensity, photoperiod, light quality, temperature, temperature fluctuations, nitrates, O2, CO2, pH, moisture, physical abrasion
Epigeous germination
cotyledons pulled out of ground -> where cotyledons are when germination occurs
Hypogeous germination
cotyledons remain in soil
common monocots
- 1 cotyledon
- onions and corn
Hypocotyl hook
hook breaks the ground open and pulls the seed behind it, protects the embryo in the seed, and pulls it out cotyledons out of the ground
Next after seed has germinated?
leaves, nodes, internodes, apical meristems -> overall morphology and how photosynthesis fits in
Epicotyl
the young shoot that is developing
