The Vernal Dam Hypothesis

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I have already established that spring ephemerals are badasses (http://bit.ly/1CsEtj1) but what I am about to tell you is really going to kick it up a notch...

While offering our native pollinators some much needed food resources along with giving us humans a much needed jolt of life after a long and dreary winter, spring ephemerals like these trout lilies (Erythronium americanum), are important nutrient sinks for forests.

Back in 1978, a guy by the name of Robert Muller put forth a very intriguing idea known as the vernal-dam hypothesis. Basically, he proposed the idea that soil nutrients are heavily leached into waterways during the spring melt and subsequent rains. Where spring ephemerals are present, they act as nutrient sinks, taking up much of the nutrients that would otherwise be lost. The idea was well liked but unfortunately, the important assumptions of this hypothesis were not tested until the last decade or so. Recently, more attention is being paid to this concept and some research is being published that do indeed support his claims!

Though the research does not address whether or not the nutrients really would be lost from the system in the absence of spring ephemerals, it is showing that some species really do serve as nutrient sinks. Trout lily, for instance, is a massive sink for nitrogen and potassium. As they grow they take in more and more. When the warmer summer weather hits and the leaves die back, they then release a lot of nutrients back into soil where vigorously growing plants are ready to take it up. It should be noted that trees will still take in nutrients even before leafing out for the summer. One study even showed that net uptake of nitrogen and potassium by a variety of spring ephemeral species is nearly equal to the net annual losses. I must admit that I did not quite understand what the "losses" are in this particular study but the evidence is tantalizing nonetheless. In one example, nitrogen uptake by ephemerals was 12% of the nitrogen in annual tree litter!

Whether or not it is shown that nutrients taken up by ephemerals would otherwise be loss is, in my opinion, beyond the point. What has been demonstrated in the ability of spring ephemeral species to uptake and store vital forest nutrients suggests major ecosystem benefit! Furthermore, when you consider the fact that mycorrhizal fungi are non-specific in most cases and will bond with many different plant species and then go as far as sharing nutrients among the forest flora, you really start to see a big picture story that has been playing out all over the world for millennia. 

Further Reading:

http://www.jstor.org/discover/10.2307/2937357?uid=3739256&sid=21102213017237

http://iub.edu/~preserve/docs/library/BlankJL_1980.pdf

http://www.jstor.org/discover/10.2307/2425383?uid=3739256&sid=21102213017237

http://link.springer.com/article/10.1007/s00442-002-0958-9#page-1

The Badass Spring Ephemerals

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Spring ephemerals and the word "badass" are probably not frequent associates but I am here to argue that they should be.

Spring ephemeral season is here for some and just around the corner for the rest of us. It's my favorite wildflower season and I often go missing in the woods for those first few weeks of spring. It is easy to look at their diminutive size and their ephemeral nature as signs of delicacy but these plants are anything but. In fact, when one examines the intricacies of their lifestyle, they can see that spring ephemerals make most other plants look like total softies.

Spring ephemerals, the designation of which gets blurred depending on who you ask, have to complete most of their life cycle in the early spring before the trees and understory shrubs leaf out and completely take over most of the available light. This is an incredibly tough time to be a plant. Soil temperatures are low, which makes nutrient and water uptake a difficult task, all but the most robust pollinators are still sound asleep, and there is the ever present danger of a hard frost or freak snow storm. These factors have led to some incredible adaptations in all of the species that emerge around this time. Whereas each species has its own methods, there are some generalities that are common throughout.

For the most part, spring ephemerals have two distinct growth phases; epigeous (above ground) and hypogeous (below ground). The hypogeous phase of growth takes place throughout fall and winter. Yes, winter. This is the phase in which the plants put out more roots and develop next season’s buds. This goes on at the expense of nutrients that were stored the previous spring. Once spring arrives and soils begin to warm, the plants enter the epigeous phase of growth where leaves and flowers are produced and reproduction occurs. This is an incredibly short period of time and spring ephemerals are well suited for the task.

Typical growth cycle of many spring ephemerals  [Source}

Typical growth cycle of many spring ephemerals [Source}

For starters, photosynthetic activity for these species is at its best around 20 °C. Photosynthetic proteins activate very early on so that by the time the leaf is fully expanded, the plant is a powerhouse of carbohydrate production. Photosynthesizing in cool temperatures comes at a cost. Water stress in at this time of year is high. Low soil temperatures make uptake of water difficult and it is strange to note that many species of spring ephemeral have very little root surface area in the form of root hairs. These species, however, have extensive mycorrhizal associations which help assuage this issue.

Nutrient availability is also very limited by low soil temperatures. Chemical reactions that would unlock such nutrients are not efficient at low temperatures. Again, spring ephemerals get around this via their increased mycorrhizal associations. It should be noted that some species such as those belonging to the genus Dicentra, do not have these associations. In this situation, these species do in fact develop extensive root hairs as a coping mechanism. Despite specific adaptations for nutrient uptake, you will rarely find spring ephemerals not growing in deep, nutrient-rich soils.

Again, we must keep in mind that all of this is happening so that the plant can quickly complete what it needs to do in the few weeks before the canopy closes and things heat up. It has been observed that high temperatures are associated with slowed growth in most of these species. As temperatures increase, the plants begin to die back. Another adaptation to this ephemeral lifestyle is an increased ability to recycle nutrients in the leaves. As spring temperatures rise, the plants begin to pull in nutrients and store them in their perennial organs. They also show specific compartmentalization of energy stores. In many species, seed production is fueled solely by energy reserves in the stem. Some underground storage structures then receive nutrients to fuel autumn and winter growth while others receive nutrients to fuel leaf and stem growth in the early spring.

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Despite all of these amazing adaptations, life is still no cake walk and growth is painstakingly slow. Many species, like trout lilies (Erythronium spp.), can take upwards of 8 years to flower! 8 years!! Think about that next time you are thinking of harvesting or picking some. Even worse in some areas are white tailed deer. East of the Mississippi their populations have grown to a point in which their foraging threatens the long term survival of many different plant species. Especially hard hit are spring ephemerals as they are the first plants to emerge after a long winter of near starvation. 

I hope this post wakes people up to how truly badass these species really are. As our climate warms, we can only speculate how things are going to change for many of them. Some research suggests that things may get easier whereas others suggest that conditions are going to get harsher. It's anyone's guess at this point. As populations are wiped out due to development or invasive species, we are losing much needed genetic diversity and corridors for gene transfer. This is yet another reason why land conservation efforts are so vital to resilient ecosystems. Support your local land conservancy today!

Spring is here and things are getting underway. Get out there and enjoy the heck out of the spring ephemerals! In a few short weeks they will be back underground, awaiting the next cold, damp spring.

Further Reading: [1] [2]

The First Forests

Have you ever wondered when the first forests appeared on Earth? What were these first forests like? What kinds of trees made up these forests? A recent fossil discovery is helping to answer some of these questions.

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The story begins back in 1870's in a quarry located in the town of Gilboa, NY. Quarry workers dug up a literal "forest" of fossilized stumps. These stumps were in still-life position and they astounded the paleontological community. The rocks they were found in were of the middle Devonian era, which would make these stumps a relic of the oldest evidence of forests on the planet. The only problem was that the upper parts of these "trees" remained elusive. For over 130 years the true identity of these ancient trees remained a complete mystery. What were they? How did they live?

Fast forward to 2004. Linda VanAller Hernick and Frank Mannolini were searching another Gilboa quarry not too far from where the stumps were first discovered. There they uncovered the fossilized crown of a fern-like tree. The following year they extracted the trunk of a large tree from the same quarry. When they looked at what they had found they soon realized they had discovered the missing pieces to the Gilboa stumps! Putting the pieces together, the researchers realized that the crown, trunk, and stumps were all pieces of the same species. 

Coined "Wattieza," the trees are not trees as we know them today. These were relatives of the ferns. They reproduced with spores, not seeds. Forests of Wattieza grew during the Devonian, some 415 to 360 million years ago. This is a major milestone in the understanding of how plants and ecosystems evolved over time. The presence of forests most likely paved the way for more diversification because forests tend to create their own microclimates as well as foster new niches. 

Photo Credit: Frank Mannolini/New York State Museum and www.nature.com

Further Reading:
http://www.nature.com/nature/journal/v446/n7138/abs/nature05705.html

Cooksonia: A Step Into the Canopy

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For plants, the journey onto land did not happen over night. It began some 485.4–443.4 million years ago during the Ordovician. The best evidence we have for this comes in the form of fossilized spores. These spores resemble those of modern day liverworts. Under high powered microscopes, one can easily see that they were indeed adapted for life on land. These early plants were a lot like the hornworts, liverworts, and mosses we see today in having no vascular tissues for transporting water, an adaptation that would not come along for another few million years. 

Without vascular tissues, plants like liverworts and mosses cannot transport water very far. They instead rely on osmosis and diffusion to get water and nutrients to where they need to be, which severely limits the size of these types of plants to only a few centimeters. This growth pattern carried on well into the Silurian. Until then, the greening of our planet happened in miniature. 

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Around 415 million years ago, however, plants became vascularized. This changed everything. It set the stage for the botanical world we know and love today. Paleobotanists place the fossil remains of these newly evolved vascular plants in the genus Cooksonia. Based on what we would call a plant today, Cooksonia probably pushes the limits. However, in some species the branching structure is full of dark stripes, which have been interpreted as vascular tissues. It still wasn't a very tall plant with the tallest specimen standing only a few centimeters but it was a major step towards a much taller green world. 

Cooksonia did not have any leaves that we are aware of but some species certainly had stomata (another major innovation for water regulation in plants). Each branched tip ended in a sporangium or spore-bearing capsule. It has been suggested that Cooksonia may not represent an individual photosynthetic plant but rather a highly adapted sporophyte that may have relied on a gametophyte for photosynthesis. This hypothesis is supported by the diminutive size of many Cooksonia fossils. They simply do not have enough room within their tissues to support photosynthetic machinery. Because of this, some botanists believe that vascularization sprang from a dependent sporophyte that gradually became more and more independent from its gametophyte over time. Until an associated gametophyte fossil is found, we simply don't know. 

Photo Credits: Steel Wool (http://bit.ly/1AjLYh8) and Sabrina Setaro (http://bit.ly/16mdyxw)

Further Reading: [1] [2] [3]

Flowers of the Underworld

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New Zealand has some weird nature. It is amazing to see what an island free of any major terrestrial predators can produce. Unfortunately, ever since humans found their way to New Zealand, the unique ecology has suffered. One of the most unique plant and animal interactions in the world can be found on this archipelago, but for how much longer is the question.

The story will start with a species of bat. In fact, this bat is New Zealand's only native terrestrial mammal. That's right, I said terrestrial. The New Zealand lesser short-tailed bat spends roughly 40% of its time foraging for insects on the ground. It has lots of specialized adaptations that I won't go into here but the cool part is these bats forage in packs, stirring up insects from the leaf litter until they reach a level of feeding frenzy that I thought was reserved only for sharks or piranhas. Along with using echo location, they also have a highly developed sense of smell. This is important for our second player in this forest drama. 

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Enter Dactylanthus taylorii, the wood rose. This plant is not a rose at all but rather a member of the tropical family Balanophoraceae. More importantly, it is parasitic. It produces no chlorophyll and lives most of it's life underground, wrapped around the roots of its host tree. Every once in a while a small patch of flowers breaks through the dirt and just barely rises above the leaf litter. This gives this species its Māori name of pua o te reinga or pua reinga, which translates to "flower of the underworld." The flowers emit a musky, sweet smell that attracts the ground foraging bats.

The bats are one of the only pollinators left for the wood rose. They sniff out the flowers and dine on the nectar, all the while being dusted with pollen. Recently, it has been found that New Zealand's giant ground parrot, the kakapo, is also believed to have been a pollinator of this plant. Sadly, the kakapo only exists on some of the smaller islands of the archipelago.

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Both the wood rose and the New Zealand lesser short-tailed bat are considered at risk of extinction. When modern man came to these islands they brought with them the general suite of mammalian invasives like rats, mongoose, cats, and pigs, all of which are exacting a major toll on the native ecology. The plants and animals of New Zealand have not shared an evolutionary history with such aggressive mammalian invaders and thus have no adaptations for coping with their sudden presence. The future of the wood rose, the New Zealand lesser short-tailed bat, and the kakapo, along with many other uniquely New Zealand species are for now uncertain.

Photo Credits: Joseph Dalton Hooker (1859), Wikimedia Commons, and Nga Manu Nature Reserve (http://www.ngamanu.co.nz/)

Further Reading:

http://phys.org/news/2012-10-flightless-parrots-burrowing-parasitic-hades.html

http://www.doc.govt.nz/documents/science-and-technical/Sfc019.pdf

http://www.edgeofexistence.org/mammals/species_info.php?id=56

Nature's Radar

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Are you sitting down? You may want to before you read this. The relationship I am about to tell you about is pretty amazing. Coevolution is never a dull topic and the following example may be one of the coolest in the living world. 

Meet Marcgravia evenia. This vining plant species is native to Cuba and, like other members of its genus, relies on bats for pollination. This is nothing new. Many plant species utilize bats as pollen vectors. Bat pollinated flowers are often quite fragrant, using powerful odors to tap into the bats keen sense of smell. Marcgravia evenia is different though. This tropical vine taps into another batty sense, echolocation. 

Right above the flowers is a dish-shaped leaf. This leaf functions as a reflector for the bats sonar! Indeed, when tested, bats were twice as likely to find plants with these dish-shaped leaves than they were if the leaves were removed. This is an incredible coevolutionary adaptation! Because the vines are rare in the wild, anything that would increase the likelihood of a bat visitation would incur a considerable selective advantage. The dish-shaped leaves do just that. According to the authors of the paper, "the leaf's echoes fulfilled requirements for an effective beacon, that is, they were strong, multidirectional, and had a recognizable invariant echo signature." Nature never fails to amaze!

Photo Credit: Ralph Simon

Further Reading:

http://www.sciencemag.org/content/333/6042/631