Twenty years ago, a green object with a mountain-like shape similar to that of an anthill was found in a pond close to the Syowa Station. Termed "moss pillars" by the discoverer, Professor Satoshi Imura (the National Institute of Polar Research), these objects were later found to be mainly aggregates of moss that also include algae, bacteria, and tardigrades and that reach a height of up to 60 cm over 1000 years. The reason for the global attention to moss pillars is that they are model organisms equipped with ideal characteristics for life in the extreme environments of the polar regions. Currently, as a pillar project of the "Earth/ Environment System" Project, together with ice core research, "data-centric" research including genetic analyses is being conducted to reveal the mechanisms of moss pillars.

Organisms found only in three locations on Earth

The mosses that comprise moss pillars are officially reported to have been found in only three locations around the world: the pond near the Syowa Station, volcanic vents in the Antarctic Peninsula, and in South America. With a size twice that of Australia, Antarctica has numerous ponds and is also home to bases operated by over 30 countries engaged in studies on and in lakes and swamps. However, there has been no report of a new moss pillar discovery in Antarctic ponds over the past 20 years. The Antarctic ponds provide more moderate conditions than the terrestrial environment, and the water temperature is between 3 and 8 °C throughout the year. Photosynthesis is possible with the light transmitted through the surface ice, and the absence of natural grazers such as fish and insects makes the environment ideal for mosses to grow freely. Why, despite this, are moss pillars so uncommon? If the moss pillars originated from spores that happened to arrive due to some type of atmospheric disturbance, it is essential to consider a condition involving an atmospheric flow that connects the peninsula and Syowa Station. On the other hand, there has been active research on the reconstruction of the ancient environment by collecting sediment cores at the bottom of the Antarctic ponds. The sediment analysis data have revealed that the mosses in the ponds arrived merely 2000 to 3000 years ago. Because the climate at that time was not much different from that of today, we are also investigating methods to elucidate the arrival of the moss spores by reproducing the atmospheric flow using scientific modeling.

Moss and mites: two survival strategies in the polar region

As explained by Professor Motoyama, our planet experiences a 100,000-year cycle of cold and warm climates. We are now near the end of the warm period, during which the mosses invaded from somewhere. However, there are said to be organisms that have survived ice ages in Antarctica. For example, lichens and mites are thought to be such species. During ice ages, both lands and oceans are covered with glaciers. Therefore, it is impossible to live on the surface of the ground near the coasts, where mosses are found today. Combining the research on the extent of Antarctica that was covered with glaciers, it is probable that those species evacuated to high mountains. A particularly interesting aspect is volcanoes with high geothermal energies. Antarctica also contains several volcanoes, and many species of lichens and mites are found in the surrounding areas. In other words, Antarctica has two types of organisms; "temporary visitors", such as mosses that arrive during warm periods but are ultimately washed away by the glaciers, and "permanent residents", such as mites that survive the ice ages. By revealing the biodiversity and patterns of such species in detail, we aim to identify the origin of moss pillars.

No need for sexual reproduction in extreme environments

Ultimately, the topic of my research focuses on the way in which organisms live in extreme environments. In such a harsh environment, it is interesting to consider how those spores arrived and persisted through generations. They are probably living on the edge in such harsh environments. For example, tardigrades are species thought to undergo sexual reproduction only when surviving harsh periods. To multiply, they use clonal reproduction only among females because sexual reproduction is inefficient. Other examples of organisms in such harsh environments might teach us basic principles of survival. In this sense, Antarctica is a truly unique place for experiments. Moreover, it is possible to consider moss pillars as an ecosystem similar to a forest or society in such environments. The integrated research program with the National Institute of Genetics and Hiroshima University has been conducting analyses of the types of organisms that live in moss pillars and the networks that they form by reading the DNA of all kinds of organisms, even unknown ones. For example, we have discovered a cycle in which certain bacteria fix nitrogen into ammonia, other bacteria convert it into nitrous acid and then into nitric acid, and after mosses absorb and use these acids, bacteria again break them down and convert them back to nitrogen.

Threads of proof spun by data and simulations

Now, why do moss pillars have such a distinctive shape? Moreover, why are they structured into surface and inner layers? It is mysterious if you think about it, is it not? Today, collaborative studies led by the Graduate University of Advanced Studies are being conducted to understand, for example, how optimization of lighting affects the growth of the shape using computer simulations. Mosses create a surface layer with pigments to block the strong UV light and conduct photosynthesis inside that layer. We are also confirming how the balance of the two layers leads to the growth of thick moss mats through calculations. For the monotonic environment of Antarctica, it is not necessary to take into account additional parameters. Therefore, we can expect high accuracy of such models and compare the calculation results to the actual outcomes. We are aiming for results that make us realize, "Ah, I did not know moss pillars have such a system!"

(Text in Japanese: Satoshi Imura, Rue Ikeya. Photographs: Mitsuru Mizutani. Published: October 10, 2014)