Closed on Account of Weather

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]

 

Arctic Bone Nurseries

Life and death are two sides of the same coin. In death, an organisms body is broken down into its constituent parts and redistributed throughout the environment. As such, decomposition is a major player in the global cycling of nutrients. Nowhere does this become more apparent than in nutrient limited habitats like the Arctic Tundra.

The Arctic is known for being quite harsh. A combination of low temperatures, low water availability, and short summers make for tough conditions for any plant. What's more, low temperatures and water availability also mean nutrients are hard to get at. It stands to reason then that any potential uptick in nutrient availability would be a boon for Arctic plant life.

This is where dead animals come in. When a large animal like a muskox dies, its body can take many years to break down. Each summer, as temperatures rise above freezing, decomposition slowly eats away at the tissues. Research has found that nutrient levels, specifically nitrogen, are much higher within a meter radius around the carcass. Plants in this region were found to have higher nitrogen levels in their tissues and achieved the most luscious growth.

Nutrients aren't the only benefit carcasses provide, they also offer a favorable microclimate. Many herbivores instinctually avoid feeding around dead animals as a way of limiting exposure to disease. Researchers found that grazing levels were lower around most of the carcasses they studied. Another benefit is shelter. Wind is an ever present force to reckon with on the tundra. Carcasses provide a sheltered area that serves as an oasis for seeds to germinate and grow. The carcass also acts like a filter, collecting debris and allowing soils to build over time. Other animals may find this a favorable place to hide or hunt and thus the importance of these carcass islands becomes all the more apparent.

Photo Credits: Neil Shubin and Brian Whitlock

Further Reading:
http://pubs.aina.ucalgary.ca/arctic/arctic55-4-389.pdf