Researchers have created a model that utilizes gene activity to forecast when the buds of Somei Yoshino cherry trees will emerge from dormancy. This discovery can enhance the precision of blooming predictions and reveal how climate change may pose a risk to flowering in the southern parts of Japan.
Every spring, Japan is renowned for its cherry blossoms, known as sakura, which bloom starting in the southern region of Kyushu and travel northward all the way to the remote Hokkaido. The Somei Yoshino cherry tree, being the most widely cultivated variety, epitomizes spring when these cloned trees bloom simultaneously at various locations, resulting in a stunning and short-lived display of white-pink flowers that captivates both locals and tourists. In anticipation of the blooming period, forecasts for Somei Yoshino are closely monitored for months, as travelers plan their visits, and locals organize various celebrations and events. However, climate change has started to alter the timing of these blooms, making them increasingly challenging to predict.
Researchers from Kyushu University and the Forestry and Forest Products Research Institute have developed a model using gene activity to anticipate when the buds of Somei Yoshino cherry trees leave dormancy. Their research, which was published on September 19 in the journal Plants, People, Planet, suggests that this model can not only refine blooming predictions but also shed light on the possible effects of climate change on flowering patterns in southern Japan.
Before the cherry trees can bloom, the buds must go through two dormancy stages: endodormancy and ecodormancy. A chilly winter is essential to exit endodormancy, while the buds need warmth in spring to transition from ecodormancy.
“The requirement for both chilling and warming creates significant unpredictability in flowering times,” says Atsuko Miyawaki-Kuwakado, the lead author and a JSPS Research Fellow (PD) at Kyushu University’s Faculty of Science. “Given the variability in autumn, winter, and spring temperatures, the blooming may occur early, be postponed, or be completely stifled.”
Once the ecodormancy phase ends, the buds rapidly begin to grow and open. However, determining when the endodormancy phase is broken can be more difficult, as the buds do not visibly change. Miyawaki-Kuwakado and Professor Akiko Satake, a senior author from Kyushu University’s Faculty of Science, believed that by examining the internal processes of the bud, they could pinpoint this crucial moment.
Starting in October, the researchers collected leaf and bud samples monthly from Somei Yoshino cherry trees across three locations in Japan: Fukuoka in the south, Tsukuba in the center, and Hokkaido in the north, documenting the most active genes at various times. They discovered that the buds generally displayed five key patterns of gene activity across the seasons—early summer, summer, autumn, winter, and spring—with each pattern closely linked to temperature variations.
Next, the researchers concentrated on the expression levels of specific genes classified as DAM, which are known to be related to bud dormancy. They identified that among the six DAM genes, the activity of DAM4 was crucial in maintaining the endodormancy phase.
“We observed that at the beginning of winter, DAM4 was highly active, but as the days progressed with temperatures below 10.1°C, the activity of DAM4 diminished. Once the temperature dropped below a certain level, the buds emerged from dormancy and began to flower when experimentally exposed to warmth,” explains Satake.
Utilizing a model based on DAM4 activity, the researchers concluded that Yoshino cherry trees need approximately 61 days of temperatures under 10.1°C for endodormancy to be broken. Analyzing historical temperature data from the Japan Meteorological Agency, they found that from 1990 to 2020, the breaking of endodormancy occurred later by about 2.3 days each decade.
In the future, weather forecasters can utilize the estimated awakening times to create more accurate predictions for when the Yoshino cherry buds will bloom. The team also aims to further refine the model to assess the potential impact of climate change on flowering times.
“Without enough cool days during winter, endodormancy cannot be broken, preventing the Yoshino buds from flowering,” warns Miyawaki-Kuwakado. “Therefore, it’s crucial to predict the effects of global warming, particularly in southern Japan, to devise strategies for mitigating these impacts.”
