In Insights we discover the story behind a recent publication in Functional Ecology. This week, Ji Suonan of Peking University and the University of Copenhagen sheds light on the differences of symmetric and asymmetric winter warming on alpine plant phenology
What is your field of expertise, and why it is important?
I am particularly interested in the phenology of alpine meadow plants. Given the cold temperatures and a short growing season on the Tibetan Plateau, plant phenology has been reported to be very sensitive to global warming. I studied plant phenology under simulated warming to elucidate the responses of alpine meadow ecosystem to projected warming on the Tibetan Plateau.
Can you give a brief summary of the paper?
As one of the most climate-sensitive and vulnerable regions of the world, the Tibetan Plateau is experiencing a rapid warming. Importantly, warming patterns will not be equal across seasons, winters are predicted to warm more than summers. While climate warming generally advances plant phenology, i.e. the leaf-out or flowering time, some studies report that winter warming has the opposite effect on plant growth. A certain amount of chilling is required to break a plants’ winter dormancy, so if winters are too warm plant development will be delayed. Our study, however, reveals that winter warming will not delay, but advance plant phenology on the Tibetan Plateau. More importantly, the impact of winter warming is more serious than the same increase in warming in other seasons. These changes are impacting plant growth, plant-animal interactions, and ecosystem feedbacks on the Tibetan Plateau.
Can you briefly explain how symmetric and asymmetric warming are manifested?
For the experimental warming treatments, infrared heating structures were established above all plots. Two medium-wave infrared heaters (1200W, 220V, 1m long, and 0.22 m wide) or their light-free control boxes, were fixed 1.5 m above the ground within each of the plots with stainless steel posts. The set-point difference in soil temperature (5 cm) between the control, regular warming, and winter warming plots were achieved by adjusting the electronic current in each plot. In the regular warming plots, electronic current was maintained at 27-28 A year-round, while in the winter warming plots it was maintained at 37 A during the non-growing season and at 17.5 A during the growing season.
How did your ideas for this research evolve during the project? Did you run into difficulties, and if so, how did you overcome them?
We have already known that symmetric year-round warming advances plant phenology, however, it was reported that winters will be warmer than summers on the Tibetan Plateau. Therefore, we started the project to study the effects of asymmetric winter warming on alpine meadow ecosystem. The process went very smoothly, the results are quite clear, we didn’t run into much difficulties.
What knowledge gaps did your research expose?
Phenological studies on the Tibetan Plateau have long relied on remote sensing. Few have reported the impact of asymmetric winter warming on phenology through experimental studies. Our study revealed that, contrary to some plant species whose phenology is delayed by an unfulfilled chilling requirement, all our targeted species advanced their phenology with winter warming. Since winter mean daily temperatures on the Tibetan Plateau are below zero, the warming amplitude in our study may not have warmed the soil enough to overcome the winter chilling threshold for phenology, or the chilling requirement might be flexible so that plants could meet their chilling requirements over shorter periods of low temperature.
Your research touches on the different effects of symmetric and asymmetric warming on plant phenology. In real world ecosystems, climate change does not manifest itself that black and whitely and will perhaps be a complex combination of the two. How could your results give insight on more complex patterns in winter warming?
Our study is the first step in exploring the effects of asymmetric warming between seasons, and so gave preliminarily findings. However, climate change could indeed be more complex in real world. Further investigations are needed to explore the effects of real climate change.
Reading between the lines, at the end of your paper you call for studies that go beyond plant ecology. Could you develop a bit further on that? How would you like to see such research evolve?
Previous studies found that phenological shifts due to experimental warming markedly altered trophic relationships between plants and insect herbivores, causing a dramatic decline of reproductive capacity on the Tibetan Plateau. Similar phenomenon could happen to the phenology of plants and pollinators, and may result in a mismatch between them. More studies should be carried on to explore the phenology of different trophic levels.
How do your findings translate to other ecological research disciplines?
Our findings could verify the results from satellite and long-term observation based studies to better understand alpine meadow ecosystems under climate change. Additionally, phenology determines the length of growing season, thus probably impacting productivity and the carbon cycle. Phenological changes could also result in shifts in species composition. Therefore, we could combine phenological studies with community studies to learn about the mechanisms of biodiversity and community assembly.
Do you have any advice for conservationists or policy makers based on your results?
Our results showed a clear pattern that asymmetric winter warming will advance plant phenology of alpine meadow a greater extent than climate warming with equal temperature amplitude between seasons. It indicates that climate change may further advance leaf out day and alleviate forage deficiency in early spring to some extent, which may benefit the livestock husbandry on the Tibetan Plateau.
One final question- when you’re not at work, what do you like to do in your free time?
If I am not at work, I like to go out of the city and spend some time in natural environment, like mountains, especially places on the Tibetan Plateau.
Read the full article on asymmetric winter warming advanced plant phenology to a greater extent than symmetric warming in an alpine meadow or the free plain language summary here.