China’s giant sinkhole is protecting an endangered magnolia tree, but may also trap its future
China’s huge sinkhole, known as king of heaven (“tiankeng” in English)while simultaneously helping and harming one of the region’s most endangered plants. They protect rare aromatic magnolia trees from the effects of climate change, but also isolate their populations, reducing their ability to adapt in the future.A new study by researchers at the South China Botanical Garden of the Chinese Academy of Sciences and the Guangxi Institute of Botany has found that these forested pits protect trees from rising temperatures and drought. However, sinkholes also prevent trees from exchanging genes with other populations, making them more susceptible to losing genetic diversity.The findings, published in the journal Current Biology, suggest that this isolation is slowly reducing the species’ ability to evolve and threatening its long-term survival.To study the genetic effects of living in these giant sinkholes, the scientists created a high-quality reference genome of aromatic magnolias and analyzed the DNA of 112 trees from 26 populations in southwestern China, including trees growing in and around the sinkholes.
Genetic Paradox in the Deep Karst
Magnolia is a rare evergreen tree that grows in the limestone landscapes of Guangxi, Guizhou and Yunnan provinces. Genetic studies have identified four distinct evolutionary lineages across its range, two of which are primarily found in the Leye Tiankeng landscape.The results revealed surprising inheritance patterns. The overall genetic diversity of the population within the tiankeng was moderate compared with the population outside the tiankeng. However, trees growing deep in sinkholes have lower genetic diversity and a much higher number of harmful mutations than trees growing nearby on the surface. This is mainly because isolated populations have very little gene flow and are strongly affected by genetic drift.“Sinkholes are more than just safe havens,” said co-author Kang Ming from the South China Botanical Garden. “They provide a stable environment that helps endangered plants survive, but their closed geography can also isolate populations and slowly reduce the genetic diversity needed for future adaptation.”
Thrive in deep shade
Despite their isolation, sinkholes remain vital to the trees’ survival due to their unique climate. The bottom of the sinkhole is cool, moist and shaded by steep cliffs.Researchers found that the tree has adapted to these low-light conditions. Genes under natural selection in the sinkhole population are related to photosynthesis and carbon fixation.
China’s giant sinkhole houses ‘paradise’ forest with plants adapted to harsh life underground
Blackout experiments supported these findings. Magnolia seedlings die quickly in strong sunlight, but survive and grow well in 50% to 90% shade, growing best in the deepest shade.“This helps explain why Magnolia officinalis is able to thrive in the cool, moist forests at the bottom of the sinkhole,” said lead author Zhu Xianliang. “The species appears to be strongly dependent on shaded conditions, especially during the early stages of growth.”
Connecting shelters to save species
Researchers say the tree’s long-term future remains uncertain. By combining species distribution models, genomic data and mutation predictions, they studied how climate change affects species.Their models suggest that future climate change will make some habitats less suitable, leaving some populations unable to adapt. Even more worrying, deleterious mutations are expected to increase over time. The gradual loss of genetic fitness may exacerbate the direct effects of climate change and further threaten species survival.Research shows that protecting isolated refugia alone is not enough to save endangered species facing rapid environmental change. To prevent aromatic magnolias from hitting an evolutionary dead end, conservation efforts must go beyond protecting the sinkholes themselves.While sinkholes should continue to be protected as safe habitats, scientists say conservation efforts must also protect nearby outside populations and natural corridors that allow plants to exchange genes. Preserving the surrounding karst landscape is important to maintain the genetic diversity needed for species to adapt.“Our results suggest that conservation efforts should protect refugia and their surrounding connections,” Kang said. “For endangered karst plants, maintaining gene flow between populations may be as important as protecting the specialized habitats on which they depend.”
Chinese researchers discover tiankeng evolutionary trap
China’s huge “hidden world”
There are more than 300 known tiankeng in China, more than any other country in the world. Most are found in the southwestern part of the country, where water slowly shaped the limestone over millions of years. Some sinkholes are so large that they have their own forests, streams and unique ecosystems deep underground.Scientists have discovered many rare plants and animals in these giant sinkholes, including species rarely seen elsewhere. In 2022, explorers discovered an ancient forest in a giant sinkhole in Guangxi. The trees in the forest are about forty meters high and the vegetation is dense. The discovery suggests that some sinkholes may still be home to plants and animals that scientists have yet to study or even discover.Scientists say these hidden ecosystems are valuable because they can help us understand how plants and animals survive in remote places. They also provide clues about how species are responding to climate change and help researchers develop better ways to protect nature in the future.
Nutrient-rich environment in a sinkhole?
Another reason plants can survive in sinkholes is the nutrient-rich environment. Early research has found that the soil at the bottom of these giant sinkholes contains higher levels of important nutrients such as nitrogen, phosphorus, calcium, magnesium and potassium than the surrounding landscape. As a result, plants absorb these nutrients more easily, allowing them to grow faster and taller despite receiving less sunlight. Scientists also found that plants in sinkholes contain less carbon than plants growing on the surface because the cool, moist environment reduces water loss, meaning they don’t need as much carbon-rich tissue to survive. These nutrient-rich conditions help create some of the healthiest and most productive plant communities in China’s karst landscapes.
