DNA captured on air filters and stored since the 1960s acts as an ecological time capsule, according to a recent publication in Nature Communications. The findings show that tiny fragments of genetic material can paint a detailed picture of life across the landscape. They also reveal a distinct decline in biodiversity over three decades.
All organisms shed cell fragments with DNA to the environment. Now, researchers have performed the largest and most detailed analysis to date of airborne DNA using filters originally used to monitor radioactive fallout.
Air monitoring filters are found at hundreds of sites worldwide. These particular filters come from a station outside Kiruna, in northern Sweden, and have been archived in a basement at the Swedish Defence Research Agency, FOI, since the 1960s. When researcher Per Stenberg learned about the archive about a decade ago, he and his colleague Mats Forsman realised what a goldmine it was.
Week after week, the filters collected DNA from all living things: plants, fungi, insects, microbes, birds, fish, and even large mammals like moose and reindeer. By sequencing the DNA, the research team was, on a weekly basis, able to identify the presence of 2,700 organism groups within several miles of the station, and track how their populations increased or decreased over 34 years.
"It was a stroke of luck that the filters had been kept – and that they were made of a material that preserves DNA. The archive turned out to be a time machine, allowing us to revisit the past and watch an ecosystem changing in almost real time," says Per Stenberg, lead author of the study conducted by researchers from Umeå University, the Swedish University of Agricultural Sciences, and the Swedish Defence Research Agency.
When the researchers looked at long-term patterns, they saw a clear decline in biodiversity in the area, from the 1970s to the early 2000s. Examples of declining organisms include birch together with wood-associated lichens and fungi. The overall decline cannot be explained by changes in the climate, but rather seems to be linked to human activities such as forest management.
Analyses of airborne DNA have been done before, but this is an entirely new and far more comprehensive approach that spans several decades. The research team used extensive DNA sequencing, machine-learning-based identification of organisms, and air-flow modelling to track the sources of the DNA. Comparisons with traditional field surveys show that the method is reliable both for identifying organisms and for detecting changes in their abundance.
"This work is the result of nine years of intense research and development. I look forward to applying these data, together with ongoing sequencing of additional filters, to a wide range of questions," says Daniel Svensson, a co-author of the study.
The study shows that existing networks of air-filter stations can be used to monitor biodiversity trends and reconstruct ecosystems in places where baseline data are missing. This is essential for predicting future changes and adapting management and restoration strategies.
"The method can also detect and track genetic variation as well as the presence of invasive species and pathogens," says Per Stenberg.
