In recognition of her outstanding research during her PhD at the Iowa State University, Lin Meng, now a postdoctoral scholar with the NGEE-Tropics project in Berkeley Lab’s Climate and Ecosystem Sciences Division, has been awarded this year’s Science and SciLifeLab Prize for Young Scientists by the American Association for the Advancement of Science.
For her PhD, which she completed in 2020, Meng used remote sensing tools to show advancing timing of spring tree greening with climate warming and light pollution mainly in cities. The research, referred to as plant phenology, adds to a growing body of scientific work that assesses plants’ responses to future warming. Meng explains the nuanced plant phenology patterns she observed in temperate ecosystems in the U.S. and Europe. You can learn more about Meng’s PhD work in her prize-winning essay published in Science.
What got you interested in plant phenology?
In the spring of 2015, my friend and I had planned to go see the cherry blossoms in a park in Beijing, China. A freezing event occurrent the day before and all we could see the next day was flowers frozen in ice and a lot of dead flowers. That experience made me think about what fluctuating temperatures and climate change might do to plant phenology.
Why is it important to study plant phenology?
To decide when to leaf up or produce flowers, plants use cues from their environment like temperature and day length. This phenology is very sensitive to climate change. Any shifts in plant phenology can affect ecosystem functions and the services they provide. Trees that turn green earlier will maximize photosynthesis season and absorb more carbon dioxide from the atmosphere, for example. But there are consequences to this phenological change. If trees grow earlier, they’ll also produce pollen earlier in the year and cause pollen season to be more severe. So, people who are allergic to pollen will suffer symptoms earlier and longer. Also, if trees start to grow earlier, their pollinators may not be ready or arrive at a time matching this early flowering. Such mismatches will affect pollination and trees could produce less fruits and affect animals that depend on those fruits.
What about plant phenology did you specifically study and find?
I looked at the impact of warming and artificial light in U.S. cities on when deciduous trees start to grow leaves in the spring and shed them in autumn. Specifically, in my first project, I used satellite images to track when plants start putting on leaves and how that phenology differed between urban centers and rural areas in 85 large cities between 2001 and 2014. I found that on average, trees turned green six days earlier in the cities compared to rural areas in the U.S, because cities were 1-3 degrees Celsius warmer.
That made me wonder how artificial light—another feature of cities—might affect this outcome. But to answer this question, I first needed to understand the impact of natural day-night lengths on plant phenology. Hence, in my second project, I turned to the Alps in Europe where it was possible to disentangle the individual effects of temperature and day length, which is otherwise very hard to do. Winters are cold and also have short days, and summer days are warm and long. I wanted to find a way to study the effect of photoperiod alone on phenology.
In the northern Alps, with increase in latitude, you have a decrease in elevation. So, the elevation and latitude effect on temperature cancel each other out and you have a very homogenous temperature across the whole region but the day lengths do change. I found that shorter days, characteristic of higher latitudes, slowed the early leafing due to warming.
This led me to ask how the timing of such spring green up and autumn leaf coloring might vary in places with similar temperatures, with or without artificial lighting, in the U.S. In this third project I found that in cities, where light pollution that artificially extended day length, trees put on leaves earlier in the spring and changed colors later in autumn.
What’s the biggest takeaway from your work?
We expect longer growing seasons in cities going forward. That means plants will absorb more carbon dioxide and improve air quality. That’s the good news. But on the other hand, leafing early could subject plants to risks from frosts. An advanced spring green-up could also result in a mismatch in timing for pollinators. Whether this shift in urban phenology will be beneficial or creates a loss for ecosystem services and human health is a question that remains to be studied.
What are you working on now at Berkeley Lab?
As a postdoc in the NGEE-Tropics project, I’m building on my previous work on large-scale ecological dynamics and expanding my research from deciduous to tropical forests. I am now looking at how rainforests in the Amazon respond to changing environments such as climate warming, increasing drought and fires. This work is particular exciting because it will inform and improve model predictions of Amazon forests under the ongoing climate change.