Nematodes uncovered: soil organisms and carbon cycling
IntroductionThe importance of soil organisms
Of these soil animals, nematodes are by far the most abundant. In fact, nematodes account for nearly 4/5 of all animals on Earth! Just one handful of soil can contain 50,000 or more of these tiny worms.
Given their importance in soils, understanding global distribution patterns of nematodes is crucial for climate modelling and, ultimately, environmental decision making. However, to date, we have had no quantitative information of the active belowground community on a large scale. To address this, we created the first global map of soil nematode distribution patterns. This map adds a crucial layer of information to the holistic view of ecosystem functioning and its response to climate change – knowledge that is essential for environmental decision making and effective restoration projects
Our researchA global collaboration
This collaboration resulted in a comprehensive dataset of 6,759 samples, taken across the world. Next, we paired this dataset with global information on soil, vegetation and climate characteristics. We then used sophisticated geospatial modelling approaches, including machine learning algorithms, to generate the first global map soil nematode abundance. This map not only shows spatial distribution patterns of soil nematodes, it also provides valuable insights into the driving forces of specific environmental variables, such as soil physiochemical and climatic conditions. As these variables can shift due to a changing climate, our map highlights the regions that are most vulnerable to climate change.
ResultsGlobal abundance of soil nematodes
Another surprising result of our research was the geospatial distribution pattern of soil nematodes. Where aboveground organisms are typically most abundant in warm, tropical areas, our maps reveal that soil nematodes are present in highest numbers in cold regions. These include the tundra and boreal forests in Alaska, Siberia and Scandinavia. In contrast, their numbers are much lower in tropical regions.
ResultsSoil characteristics drive soil nematode abundance
In contrast to aboveground animals, where climatic conditions are strong drivers for their distribution, soil characteristics are key in regulating soil nematode abundance. By far the most important driving variable of soil nematode abundance is soil carbon. The high soil organic carbon stocks found in tundra and boreal forest soils are the prime reason for the high nematode abundances in these regions. However, nematodes are abundant in warm regions too, particularly in tropical peatlands, for example in the Peruvian Amazon. Just as sub-arctic regions, these soils are characterized by high carbon stocks.
ResultsNematode abundance and the climate
To date, the low temperatures in sub-arctic regions has restricted activity of soil organisms, including nematodes. With climate models unanimously predicting elevated temperatures in these regions, this might change. Higher temperatures can lead to increased decomposition rates, due to in raised activity and respiration rates of soil organisms. As a result, soils might lose carbon even faster than previously anticipated.
Our maps show, for the first time, the active belowground community on a global scale. This knowledge provides the first steps towards representing soil ecological processes into global biogeochemical models to predict elemental cycling under current and future climate scenarios.