Serotiny
Serotiny in botany simply means 'following' or 'later'.
In the case of serotinous flowers, it means flowers which grow following the growth of leaves,[1] or even more simply, flowering later in the season than is customary with allied species. Having serotinous leaves is also possible, these follow the flowering.
Serotiny is contrasted with coetany. Coetaneous flowers or leaves appear together with each other.[1]
In the case of serotinous fruit, the term is used in the more general sense of plants that release their seed over a long period of time, irrespective of whether release is spontaneous; in this sense the term is synonymous with bradyspory.
In the case of certain Australian, North American, South African or Californian plants which grow in areas subjected to regular
Possible triggers include:[2]
- Death of the parent plant or branch (necriscence)
- Wetting (hygriscence)
- Warming by the sun (soliscence)
- Drying atmospheric conditions (xyriscence)
- Fire (pyriscence) — this is the most common and best studied case, and the term serotiny is often used where pyriscence is intended.
- Fire followed by wetting (pyrohydriscence)
Some plants may respond to more than one of these triggers. For example, Pinus halepensis exhibits primarily fire-mediated serotiny,[3] but responds weakly to drying atmospheric conditions.[4] Similarly, Sierras sequoias and some Banksia species are strongly serotinous with respect to fire, but also release some seed in response to plant or branch death.
Serotiny can occur in various degrees. Plants that retain all of their seed indefinitely in the absence of a trigger event are strongly serotinous. Plants that eventually release some of their seed spontaneously in the absence of a trigger are weakly serotinous. Finally, some plants release all of their seed spontaneously after a period of seed storage, but the occurrence of a trigger event curtails the seed storage period, causing all seed to be released immediately; such plants are essentially non-serotinous, but may be termed facultatively serotinous.
Fire-mediated serotiny
In the
Since even non-serotinous
The relative importance of serotiny can vary among populations of the same plant species. For example, North American populations of lodgepole pine (Pinus contorta) can vary from being highly serotinous to having no serotiny at all, opening annually to release seed.[12] Different levels of cone serotiny have been linked to variations in the local fire regime: areas that experience more frequent crown-fire tend to have high rates of serotiny, while areas with infrequent crown-fire have low levels of serotiny.[3][13] Additionally, herbivory of lodgepole pines can make fire-mediated serotiny less advantageous in a population. Red squirrels (Sciurus vulgaris) and red crossbills (Loxia curvirostra) will eat seeds, and so serotinous cones, which last in the canopy longer, are more likely to be chosen.[14][15] Serotiny occurs less frequently in areas where this seed predation is common.
Pyriscence can be understood as an adaptation to an environment in which fires are regular and in which post-fire environments offer the best germination and seedling survival rates. In Australia, for example, fire-mediated serotiny occurs in areas that not only are prone to regular fires but also possess
Evolution
Serotinous adaptations occur in at least 530 species in 40 genera, in multiple (paraphyletic) lineages. Serotiny likely evolved separately in these species, but may in some cases have been lost by the related non-serotinous species.
In the genus Pinus, serotiny likely evolved because of the atmospheric conditions during the Cretaceous period.[5] The atmosphere during the Cretaceous had higher oxygen and carbon dioxide levels than our atmosphere. Fire occurred more frequently than it does currently, and plant growth was high enough to create an abundance of flammable material. Many Pinus species adapted to this fire-prone environment with serotinous pine cones.
A set of conditions must be met in order for long-term seed storage to be evolutionarily viable for a plant:
- The plant must be phylogenetically able (pre-adapted) to develop the necessary reproductive structures
- The seeds must remain viable until cued to release
- Seed release must be cued by a trigger that indicates environmental conditions that are favorable to germination,
- The cue must occur on an average timescale that is within the reproductive lifespan of the plant
- The plant must have the capacity and opportunity to produce enough seeds prior to release to ensure population replacement[2]
- Serotiny must be heritable[17]
References
- ^ a b Goodrich, Sherel (31 October 1983). "Utah flora: Salicacea". Great Basin Naturalist. 43 (4): 536. Retrieved 1 December 2020.
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- ^ Beaufait, WR (1960). "Some Effects of High Temperatures on the Cones and Seeds of Jack Pine". Forest Science. 6: 194–199.
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