The rock, gravel, sand and fine particles that are trapped under glaciers for millennia undergo major changes as glaciers retreat. Once they are exposed to the atmosphere, they are colonized by a variety of organisms and develop soils. They shift from having relatively few species of bacteria to developing more complex ecosystems.
Studying nematodes — or roundworms — communities in these soils can provide insight into the stages of ecosystem development as the worms respond differently to vegetative changes from grasslands to forested areas, a recent study from the Chinese Academy of Sciences found. The types of nematodes found in soil can also give insights about soil health, the authors found.
Though they may not look very impressive, nematodes are complex creatures. More than 25,000 species have been identified and have been known to adapt to a large variety of environments — from terrestrial to watery ecosystems, from salty to fresh habitats, and from northern to southern longitudes.
The Hailuogou Glacier on the southeastern Tibetan Plateau in China has retreated 1.8 kilometers in the 20th century, according to glaciologist Mauri Pelto. Because of the glacier’s rapid retreat, researchers from the Chinese Academy of Sciences were able to observe 120 years of plant regeneration in seven different stages. In phase one–the first 3 years after soil is initially exposed–mosses, small plants and grasses begin to grow. During phases two, three and four, or years 3 through 40, grasses eventually become replaced by shrubs and low trees. In phases five, six and seven, from 40 to 120 years after exposure, mature forests develop. Samples of these phases were taken from seven different sites and analysed for pH balance, phosphorus and nitrogen content. Nematodes were extracted from the samples.
The researchers found that while all these changes were occurring above ground, dynamic changes were also occurring beneath the surface. As the soils first developed, levels of soil phosphorous increased, and fungi-eating nematodes were dominant. In later stages, these nematodes were replaced with bacteria-eating nematodes; this shift is likely a response to the improvement of soil quality.
But by the seventh phase, soil health began to decrease, and the researchers noticed the return of fungi-eating nematodes, species that survive well in poor soil conditions. Nutrient availability at this later phase began decreasing, suggesting that the ecosystem was entering a retrogressive phase.
“Further research should be conducted to determine the most efficient approach to integrate plant succession, nutrient availability, and soil bacterial and invertebrate community dynamics into models of ecosystem development and succession,” the researchers concluded. “These models would be helpful for prediction and management of nutrient limitation during long-term soil development.” It will be interesting to see whether the patterns of changing nematode populations in the glacier forelands in China are similar to those in other areas. It will also be of importance to framing climate change policy, since the expansion of vegetation in areas formerly covered by glaciers has the potential to sequester carbon dioxide.