The presentation for our noon meeting on November 29 was by Dr. Diana Wall, the head of CSU’s School of Global Environmental Sustainability, who works on soil biodiversity and ecosystem functioning, especially in the dry valleys of Antarctica. She commented that she has spent the last 28 Christmases in Antarctica where she studies the soil of the dry valleys to increase our understanding of how climate change may affect terrestrial ecosystems with its implications for effects in more temperate settings. Specifically, she is interested in the effects of changes in temperature and precipitation on the biota, ecosystem functions, and habitat. The advantages of working with the soils of the dry valleys include that the species diversity is reduced so species relations are easier to determine, there are no non-native species with which she has to contend, and the denizens are sensitive to climate change.
Across the 4800 square kilometers of the dry valleys (with local summertime flowing streams and a lake), she and her team are working to understand which species are there, where they live and why, how they respond to the environment, and what they do in the ecosystem. Amazingly, some 59% of life on earth is estimated to be below ground so understanding the ecosystems of soils has significant implications for soil diversity, biocontrol, food for wildlife above-ground, clean water, carbon storage, erosion control, and human health and well-being. In the dry valleys, nematode roundworms (around the size of a human eyelash) are the dominant multicellular life form; in fact, four of five animal species on earth are nematodes; they are aquatic animals that live in films of water around soil particles and eat a broad range of bacteria, fungi, algae, plant roots, other nematodes, and small animals so they are an important part of a complex food web. The two biggest challenges in the dry valleys involve water: freeze-thaw cycling (including production of antifreeze proteins) and desiccation (anhydrobiosis – they dry out completely and “come back to life” when they get wet again).
Dr. Wall talked briefly about the logistics of doing science in Antarctica. Although numerous countries have interests there and some have claimed parts of the continent in the past (but those claims are inactive due to the Antarctic treaty), the US has a major presence there with two major installations, McMurdo (focusing on research on land) and Palmer (focusing on marine research). Getting there burns a lot of carbon, including an 8-hour flight from New Zealand to the ice. While doing field research, there are never less than two people in a group for safety. In order to maintain the pristine nature of the continent, everything is carried in and then carried out, leaving only footprints (which can last for at least 15 years). During the summer field season, there are 24 hours of daylight. The soils in the dry valleys are carbon-poor and salty and, even with sufficient moisture to support the nematodes, always feel dry since the average annual precipitation is around 4 cm/year water equivalent. The soils may be up to 10,000 years old. The average surface air temperature and the average surface soil temperature are around zero degrees Fahrenheit, although the soil can reach a high of 780 F and a minimum of -600 F.
The understanding of life in the dry valleys began with Scott in 1903 declaring that there was no living thing. Later, more focused studies, found mosses and lichens in the 1960s, bacteria and a few nematode species in the 1970s, and finally nematodes dominating the dry soils in 1990. It is now known that nematodes are the most abundant and widespread land animal of Antarctica, the top of the food chain in the dry valleys, and a major player in nutrient cycling. One nematode, Scottnema sp., is the most widely distributed metazoan in the dry valleys, abundant in dry soils (it is the only invertebrate species in the driest soils), but only low abundance and patchy distribution in wet soils. It is estimated that the global soil nematode biomass equals 82% of the total human biomass on earth and that CO2 respired by nematodes is equivalent to 2.2% of the total carbon emissions from soils. This is significant because, over a 12-year cooling cycle in the dry valleys, there was a 65% decline in Scotnema (the organism at the top of the food web) resulting in a 30% reduction in soil carbon cycling.
The studies that Dr. Wall’s team effect include observation, field and lab manipulation, and geographical gradients. They use “baby greenhouses” where they can control the amount of water. Elevation transects allow mapping of abundance of species across water gradients (wet to dry areas). Recording of temperatures with time showed that average temperature decreased from 1985 to 2000 (coinciding with a decrease in abundance of nematodes) and then increased from 2000 to 2015 (coinciding with an increase in nematodes), the rising temps associated with more frequent “heat waves” and pulses of water availability. From these data along with experimental warming in the lab, they predict that, if the valleys get warmer and wetter, they will begin to look more like Patagonia. Alternatively, if the valleys get warmer and dryer, they will begin to look more like Mars. In detail, they predict that wetter will result in the decline of the dominant species and increase in the current subordinate species.
Questions:
Why did you develop a passion for Antarctic soil worms? She was interested in trying to decipher what a species does. In warm deserts, there was simply too much diversity and abundance whereas in the cold deserts (as in Antarctica), everything was simpler and more amenable to understanding.
How did they determine that a decrease in temperature resulted in the nematodes dying? They could take a sample of the soil back to the lab and, in 24 to 48 hours, extract the nematodes and then see trends in juveniles vs adults, males vs females. They found that with decreasing temperature, there were fewer juveniles indicating a decrease in population with decreased temps.
How can you tell if a nematode is dead or just completely dried out? If they extracted the nematodes from the soil sample with sugar water, the worms would be dry. If they were alive, then wetting them with pure water would bring them back to life if only dry, but not if they were dead.
Was there any connection between nematode abundance/health and the microbiology of the soil? She couldn’t comment on that since she has not been involved in any microbiological studies. However, there are people doing that and there may be results in the future.