Thesis Christ: With Water in the Air, Can the Trees Still Drink?

Biology major Shannon Wells-Moran shares his research

Droughts are, unsurprisingly, very bad for trees, especially for their roots. Shannon Wells-Moran ‘21 explains, “how trees take up water from their roots is that they rely on the evaporation out of their leaves to create this pressure potential that essentially sucks the water up the stem like a straw. And if air pockets form [due to a drought], water can't cohere to itself, and it'll stop being sucked up. So enough of these little embolisms will kill a tree.” However, some studies have found that marine fog helps Coast Redwoods relieve this type of drought stress. Wells-Moran is studying the mechanism for this phenomenon in his Biology thesis this year.

Picture this: You’re walking in a forest, and suddenly you come upon a giant tree with leaves as big as your hand, and every inch of it covered in moss. This image is what inspired Shannon Wells-Moran to research for his thesis. As a biology major, Wells-Moran has always been interested in the plant life of the West Coast. While studying the trees in the area, he noticed that Big-Leaf Maples had an inordinate amount of moss on them compared to the other nearby trees. This reminded Wells-Moran of the thesis his friend, Purna Post-Leon ‘20, did the previous year. Post-Leon based her thesis off of a previous study about the absorption of water through the bark of trees. She felt this study had a problematic research setup and did not come to a satisfying conclusion regarding the question. She tested the methods of the previous study that concluded that water enters Redwoods through the bark but found that the method used for the branches to absorb water was faulty and prone to leaks, which calls their conclusion into question. 

Wells-Moran hopes to change this. When Wells-Moran looked at all the moss on the Big-Leaf Maple, he remembered Post-Leon’s study and wondered if there was a symbiotic relationship between the moss and the trees through the transfer of water. Wells-Moran and Post-Leon designed a better method over the summer to answer this question. “I am essentially serving as the third copy editor on this, and I'm going in with a new method that I think will work to try and replicate these findings,” says Wells-Moran.

Wells-Moran decided to study three different species of trees in his experiment: Coast Redwood, Douglas Fir, and Big-Leaf Maple. The Coast Redwood was the tree studied in the original research, Post-Leon added the Douglas Fir, and Wells-Moran noticed the potential connection between the existing research and the moss on Big-Leaf Maples. He is using deuterium oxide, a water molecule made with stable hydrogen isotopes, to test if water can get into the branch. 

“I’ve taken branches off of several trees, and I'm keeping them in the lab. And over the course of 48 hours, I apply this special tagged water to the bark, and then I let them take that up. They're still photosynthesizing. They're still respirating over the course of the next 48 hours. And then I see if any of that water has made it into the branch.” says Wells-Moran. He does so by stripping the bark off of the branches and heating the branches up in bags to draw out and collect the water. This way he is able to track if the irradiated water entered the branch. In order to do so, he needs an isotope ratio mass spectrometer, which unfortunately means he needs to send his samples to UC Davis to use theirs, as Reed does not have the expensive machine.

While sending his samples away isn’t a huge issue in the grand scheme of things — as well as a much preferable solution to buying the machine — some issues were not so easily resolved. “It has been very tricky doing a lab thesis during COVID. There are a lot of regulations in place in the department about how many people you can have in lab at any given time,” says Wells-Moran. This means he only has so much access to the lab in the best-case scenario, which he hasn’t found himself in recently. Almost immediately into the school year, he had to quarantine for two weeks due to an exposure risk. He’s fine, but it did take a lot of lab time away. Not only that, but just after he was released from quarantine, the snowstorm hit, which meant he couldn’t go out and collect samples. Despite these issues, Wells-Moran’s research continues to progress.

Wells-Morans’s research could be instrumental to understanding how trees intake water, but it still would not explain why Big-Leaf Maples would have so much more moss compared with other trees, or if the two situations are related at all. Even if he finds this symbiosis, the rate of water intake would need to be studied in order to have more practical applications outside of a lab. As climate change causes droughts to occur more frequently, perhaps a future Reedie can take up the torch and continue expanding our knowledge of how we can protect trees from ourselves and the destruction we’ve caused.