Plants growing at the bottom of China’s “Tiankeng” sinkholes have significantly higher nutrient levels compared to those growing outside the sinkholes, thanks to the unique conditions of moisture and soil within these depressions.
According to a study published in the journal Plant Ecology, reported by Live Science on July 30, various plant species thriving at the bottom of the enormous sinkholes in China absorb nutrients to such an extent that they grow much faster than plants on the surface. These sinkholes, known as “Tiankeng”, are among the last remaining natural habitats of ancient forests and may harbor some scientifically unknown species. However, researchers are still unclear about how these plants grow in such deep holes.
Ancient plants thriving inside the Tiankeng sinkhole. (Photo: Earth)
Laurel, nettle, and ferns flourish due to the vast reserves of nitrogen, phosphorus, potassium, calcium, and magnesium present in these sinkholes. With these nutrients abundant in the Tiankeng, plants absorb them to grow tall and take advantage of the limited light that reaches them. According to the research team led by Thomas R. Sharp from Wildlife SOS in Utah, USA, plants can adapt to adverse environments by adjusting their nutrient composition.
Tiankeng are deep sinkholes, about 100 meters deep, located in the limestone mountains of southwestern China. They host many moisture- and shade-loving plant species, including endemic species from the region. Due to the towering cliffs and steep terrain of the Tiankeng, these areas are less disturbed by human activity. The Tiankeng are home to modern limestone forest plants, including Nepalese chebulic myrobalan (Choerospondias axillaris) and indigo plant (Strobilanthes cusia).
In the study, the authors collected samples from 64 plant species both inside and outside the Tiankeng in Leye County, Guangxi Province, China. Leye County is home to the Dashiwei Tiankeng cluster, a geological wonder comprising 30 sinkholes over an area of 20 km2. To determine whether nutrient absorption and growth strategies differed depending on the environment, the research team measured carbon and nutrient levels in each sample. Plants growing inside the Tiankeng had lower carbon levels than those outside, but other elements, such as calcium and potassium, were at higher levels.
Carbon is essential for plants, forming a major part of their structure and enhancing their water retention capabilities. However, the moist conditions inside the Tiankeng mean that plants can still grow with lower carbon levels in their tissues, as they do not need to store as much water. Plants growing on the surface need to collect more carbon, likely due to the high light intensity, rapid evaporation, nutrient-poor soil, greater human interference, and higher susceptibility to soil loss outside the sinkhole.
Compared to surface plants, plants growing in the Tiankeng exhibit higher levels of nitrogen and phosphorus, both of which they extract from the soil. The soil at the bottom of the Tiankeng contains more of these elements than surface soil, revealing that plants can more easily absorb nutrients. Limestone soil is also rich in calcium and magnesium. Plants in the sinkhole have a higher ratio of these elements compared to those outside and also possess higher potassium levels, even though potassium is relatively scarce in limestone soil.
“The nutrient status of the soil in the Tiankeng is excellent, and plants have evolved to make the most of the available resources to grow rapidly and capture more light,” the research team concluded.
