Fia Bengtsson, Lund University and Norwegian Institute of Nature Research, discusses her article: Rapid shifts in bryophyte phenology revealed by airborne eDNA
Most of us walk past mosses and liverworts without really noticing them. But these small plants, known as bryophytes, are vital to ecosystems, including in Arctic and sub-Arctic regions. They retain water, regulate nutrients, constitute important biodiversity, and are the ecosystem engineers that have formed massive carbon stores in the northern boreal peatlands.
Because of their physiology, bryophytes react in a very direct way to their environment, making them potential indicators of climate change. For example, because they have no roots or vascular system, they take up water and lose it depending on the surrounding moisture. But many species are elusive and hard to monitor; they may be hard to find and identify correctly. And in particular, their sporulation is hard to monitor.
Why bryophyte spores matter
Bryophytes have spores that they spread by releasing them into the wind (mostly) from capsules that are formed during a limited time of the year. Phenological shifts – changes in the timing of biological events, such as spore release – are important to monitor as they may indicate changes in diversity or biomass of species. The phenology of said sporulation is very hard to monitor because you cannot see many differences between spores from different taxa in a microscope. This means that you must monitor sporophyte (capsule) maturation in situ. This has been done for some species, but the data is limited.
DNA in the air: A hidden archive
A team of researchers at Umeå University created a time-series of environmental DNA (eDNA) from the air above Kiruna, Northern Sweden, from glass fibre air filters that had been collected and stored every week since the 1970s’ (Karlsson et al. 2020; Sullivan et al. 2023). Originally, the filters were collected to monitor radioactive downfall, but the Umeå team could extract and sequence DNA caught in the filters. By matching DNA sequences to known taxa, they found out that a large proportion were from bryophytes.
Then us bryologists got involved. The Kiruna data set meant that we could recreate the timing of spore release between 1974 and 2008, as we can assume that most of the present bryophyte DNA fragments in the air are of spore origin. The limitations of available genomic reference data meant we had to limit the investigation to specific genera. We chose 16 taxa that we knew are present in the region, have only one or a few common species there, and have enough genomic references to make identification possible.
When spring comes early
Our results shocked us a bit. On average, the start of the spore release season has advanced by four weeks since the 1970s, and the mid-season has shifted by six weeks. In some species, this means peak spore dispersal now happens nearly two months earlier than it did in the 1970s. The end of the season was more variable – some species delayed spore release – but overall, the dispersal season has become significantly longer for most species.
Why the change? Global temperatures have been rising, especially in the north. Using temperature data from the region for the period of the time-series, we could see that especially the third and fourth quarters of the previous year were correlated with the timing of increased spore release. We think it is likely that warmer conditions in autumn allow bryophytes to reach later developmental stages before entering dormancy, which could in turn lead to earlier sporophyte maturation when spring returns.
What this means for the future
Our study is the first to show phenological shifts in spore dispersal of multiple bryophyte taxa over time, consistent with climate change. In contrast to data based on field observations and herbarium specimens, we were able to quantify the annual patterns of spore dispersal and to detect phenological changes over decades. When comparing our northern data to older studies from further south, we see that the phenology of bryophytes in the far north is approaching the timing in southern Europe.
In our study, we highlight a powerful new tool: the use of airborne eDNA for biodiversity and phenology monitoring. With increased availability of genomic resources, eDNA can offer a low-cost, non-invasive, and scalable way to monitor changes in biodiversity, especially for organisms that are hard to observe directly.
As the climate continues to warm, having detailed records of how various organisms respond will be key to predicting future ecosystem changes and to planning conservation efforts. Thanks to this unique 35-year time-series that we got to work with, we uncovered how the timing of spore release in 16 different bryophyte genera has shifted dramatically – offering both a glimpse into bryophyte phenology and a powerful new way to track climate-driven changes in ecosystems.
