Aya Permin: Bryophyte-associated nitrogen fixation in a tropical mountain cloud forest—rates and responses to climate change

In this new post, Aya Permin, a new ecological researcher at the University of Copenhagen, Denmark, discusses her paper—High nitrogen-fixing rates associated with ground-covering mosses in a tropical mountain cloud forest will decrease drastically in a future climate—which has won the 2022 Haldane Prize for Early Career Researchers!

About the paper

Bryophytes (mosses, hornworts, and liverworts) are known to host nitrogen (N2)-fixing bacteria. These bacteria are capable of transforming the atmospheric N2 gas—inaccessible to organisms—into bioavailable N that can be taken up by plants and, in this way, incorporated into the ecosystem.

View on a tropical mountain cloud forest (TMCF), Peru (credit: Aline B. Horwath)

In this study, for the first time, we quantified N2 fixation activity associated with several common bryophytes (epiphytic liverworts and ground covering mosses) collected in the tropical montane cloud forests (TMCF) of Peru. Further, we identified how bryophyte associated N2 fixation activity responds to climate change (changes in temperature and bryophyte moisture level). In particular, we hypothesized that climate change (increased temperature and decreased bryophyte moisture) will decrease bryophyte-associated N2 fixation. Our study showed that N2 fixation rates associated with ground-covering moss species were up to 2 kg N ha-1 yr-1, which is comparable to other N inputs (e.g. N deposition) in the TMCF. This indicates that almost half of new N entering these ecosystems comes from bryophyte-associated N2 fixation. Further, while an increase in temperature showed little effect on N2 fixation, low moisture levels significantly suppressed N2 fixation activity.

View inside a tropical mountain cloud forest (TMCF), Peru (credit Aline B. Horwath)

Our results demonstrate the importance of N2 fixation associated with ground-covering mosses as an N source in TMCFs and suggest that predicted future declines in precipitation in these systems will reduce N inputs from bryophyte-associated cyanobacteria. Thus, our study revealed, for the first time, a potential large source of N that has been ignored so far, and increases our ability to understand and predict the consequences of climate change on TMCFs.

About the research

Bryophytes, and mosses in particular, are a major part of the ground covering vegetation in many high latitude ecosystems like boreal forest and tundra ecosystems. Thus, bryophyte ecology—including moss-associated N2 fixation—has been relatively well studied in these ecosystems.

In boreal forests, for instance, N2-fixing bacteria associated with mosses are responsible for up to 50 % of total ecosystem N input, sustaining plant productivity. Since many of these high latitude ecosystems are N-poor, the contribution of moss-associated N input are of particular interest. Yet, how widespread associations between mosses and N2-fixing bacteria are in other forests, remains unknown. TMCFs harbor a high diversity and abundance of bryophytes, thus, bryophyte-associated N2 fixation is a potentially important N input in these pristine forest ecosystems. In this study, we wanted to expand the ecosystem range where bryophyte-associated N2 fixation is studied and to increase our knowledge on how widespread this association is and how it is affected by climate change. The fact that bryophytes do not have roots and that they are fairly easy to keep in growth chambers makes them a great study organism.

Thuidium peruvianum shoot at ×200 magnification under UV-fluorescence microscope. Nostoc sp. colonies are seen in bright red between moss leaf and stem in green (credit: Aya Permin)

To follow up on this study, we have compared moss-associated N2 fixing bacteria from this study with moss-associated N2 fixing bacteria from boreal forests, including their N2 fixation activity and the bacteria community composition. In this way, we hope to increase the knowledge on the drivers of moss-bacteria association across different ecosystems.

How does it feel to win the 2022 Haldane Prize?

I feel super proud and honoured to win the 2022 Haldane prize. It means a lot that my work is acknowledged in this way. Also, I think it is very cool that a paper on bryophytes has won the prize, since they are often overlook in my opinion! 

About the author

Aya Permin (credit: Matthias Köppe)

I grew up in the countryside of Denmark in a large hippie commune where we had organic farming. Thus, from an early age, I have been exposed to the idea of seeing things as a part of and connected to a broader context. When I started studying biology, this mind-set which was instilled in an early age quickly got me interested in the field of ecology. I am fascinated, both personally and professionally, by interactions in nature and enjoy observing nature. For me, moss ecology, including how moss interacts with its environment, has many fascinating and still undiscovered aspects—I do not think I will ever get tired of wondering about moss ecology. For me, this curiosity about my research is very important and is what keeps me motivated.

I first got interested in mosses during my early biology studies when I designed a project with another student about using mosses as indicators for ecosystem condition. Since then, my interest has evolved and I was lucky to go to northern Sweden during my Master’s and PhD research where my fascination of mosses was highly stimulated by the moss-dominated ecosystem found up there.

I am a parent of two kids, and my devotion to my research has sometimes been at the expense of our family. Luckily, I have had the opportunity to bring my family when going to the field—both in northern Sweden and to Greenland!

Find the winning article: “High nitrogen-fixing rates associated with ground-covering mosses in a tropical mountain cloud forest will decrease drastically in a future climate” as well as the shortlisted papers for the 2022 Haldane Prize in this virtual issue. 

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