I am born and raised in the suburbs of Copenhagen, Denmark. At the age of 6, I joined the scouts, and I think this is where my first familiarization with nature comes from. Later in high school, I elected ‘Biology’ as one of my primary courses and for my first home assignment I got my first failing grade! I just did not get it. For the next two years I tried to figure it out and by the end of it I got it and did great for my finals. After my graduation, this experience made me apply to become a student in Biology at the University of Copenhagen. Ecology was always my favorite branch because I could “see” what was happening and because it was the subject most puzzling to me.

I was a bachelor student when I almost fell into a “real” research project. The project was about nitrogen fixation in bryophytes, and I got to spend 6 weeks in the mountains close to Abisko Scientific Research Station in northern Sweden. Long hikes to the field site, long days in the field performing incubations, staring at the view, getting sunburned and soaked in the rain and back again to the gas chromatograph to process my samples. I am a Danish city girl, and I was sold!

My primary interest in bryophytes is to discover their functions in the ecosystem. I am an ecologist and I try to understand how bryophytes respond to environmental changes and how they affect the ecosystems they are a part of. Bryophytes are spectacular plants in their own right, while they are also substrate for other plants and animals.

I did my Phd at Umeå University with Ellen Dorrepaal as my principal supervisor. David Wardle and Marie Charlotte were my co-supervisors from the Swedish Agricultural University in Umeå. Ellen and I were lucky to be based out of the Abisko Scientific Research Station right at the edge of the Abisko Nationalpark, surrounded by mountains. I investigated if bryophytes influence vascular plants responses to climate changes. I mainly relied on experimental approaches in the field and using greenhouse experiments. I lived in Abisko for 5 years during my work. Here I became familiar with the Subarctic climate year around and got a sharpened understanding for the “off” season. Bryophytes are active before and after many vascular plants have leaves.

I am a dedicated data scientist and ecologist with a passion for understanding bryophytes’ ecosystem functions. Although identifying bryophyte species is not my forte, I am committed to improving the resolution of bryophytes in plant ecology studies. Do bryophytes that appear similar have comparable functions? If so, can we group them to form functional units? With my work, I hope to encourage ecologists to include bryophytes with increased resolution in their studies and thereby enrich our understanding of ecosystems where these plants play crucial roles.

My research continuously diverges, but somehow, I am never far from where it all started, in the mountains around Abisko, with bryophytes and finding out what they do and how they differ.

På dansk:

Mit navn er Signe Lett og jeg er født og opvokset i Københavns forstæder. Siden jeg var 6 år, har jeg været spejder, og jeg tror, ??at det er her, mit første kendskab til naturen kommer fra. Senere i gymnasiet valgte jeg ‘Biologi’ som et af mine højniveaufag, og i min første hjemmeopgave fik jeg min første dumpekarakter! Der var noget jeg ikke forstod. De næste to år prøvede jeg at knække koden, og til sidst blev det tydeligere og klarede mig virkeligt godt til min eksamen. Jeg blev student, var oplevelsen af at lykkes med det mystiske fag, fik mig til at søge ind på Københavns Universitet for at læse biologi. Økologi var altid min yndlingsgren af biologi, fordi jeg kunne “se”, hvad der skete, og fordi det var det der stillede mig mest undrende.

Jeg var en bachelorstuderende, da jeg næsten faldt ind i et “rigtigt” forskningsprojekt. Projektet handlede om nitrogenfiksering i mosser, og jeg kom til at tilbringe 6 uger i bjergene tæt på Abisko Videnskabelige Forskningsstation i det nordlige Sverige. Lange vandreture til vores feltstudie, lange dage i felten, lave inkubationer, stirre på udsigten, blive solbrændt og gennemblødt i regnen og tilbage igen til gaskromatografen for at behandle prøver. Jeg er en dansk bypige, og jeg var solgt!

Min primære interesse for mosser er at undersøge deres funktioner i økosystemet. Jeg er økolog, og jeg forsøger at forstå, hvordan mosser reagerer på miljøændringer, og hvordan de selv påvirker de økosystemer, de er en del af. Mosser er spektakulære planter i sig selv, samtidigt med de også er substrat for andre planter og dyr.

Jeg fik min Ph.d. fra Umeå Universitet med Ellen Dorrepaal som hovedvejleder. David Wardle og Marie Charlotte Nilsson var min medvejledere på Sveriges Landbrugsuniveristet i Umeå. Ellen og jeg var heldige at være stationeret på Abisko Scientific Research Station lige ved kanten af ??Abisko Nationalpark, omgivet af bjerge. Jeg undersøgte, hvordan mosser påvirker karplanters respons på klimaændringer. Jeg var primært afhængig af eksperimentelle metoder i felten og brug af drivhusforsøg. Jeg boede i Abisko i 5 år under mit arbejde. Her blev jeg bekendt med det subarktiske klima året rundt og fik en skærpet forståelse for perioden der ligger uden for det vi kalder vækstsæsonen. Mosser er aktive før og efter mange karplanter har blade.

Jeg er en dedikeret kvantitativ økolog med en og ønsker at forstå mossernes økosystemfunktioner. Selvom det ikke er min styrke at identificere mosarter, er jeg optaget af at forbedre ’opløsningen’ af ??mosser i planteøkologiske undersøgelser fra bare ’mosser’ til et højere detaljeringsniveau. Har mosser, der ligner hinanden, sammenlignelige funktioner? Hvis ja, kan vi gruppere dem til at danne funktionelle enheder? Med mit arbejde håber jeg at lette muligheden for økologer for at inkludere mosser med øget opløsning i deres studier og derved berige vores forståelse af økosystemer, hvor mosser spiller afgørende roller.

Min forskning divergerer hele tiden, men på en eller anden måde er jeg aldrig langt fra, hvor det hele startede, i bjergene omkring Abisko, med mosser og i gang med at finde ud af, hvad de laver, og hvordan de adskiller sig fra hinanden.

Website: signelett.weebly.com

Publication list: https://signelett.weebly.com/publications.html

Selected publications:

Lett S, Christiansen CT, Dorrepaal E, Michelsen A (2024) Moss species and precipitation mediate experimental warming stimulation of growing season N2 fixation in subarctic tundra. Global Change Biology. DOI: https://doi.org/10.1111/gcb.17401

Van Zuijlen K, Kassel M, Dorrepaal E, Lett S (2024) Climate change effects on frost damage in subarctic bryophytes. Journal of Ecology. DOI: 10.1111/1365-2745.14236

Jessen M-T, Krab EJ, Lett S, Nilsson MC, Teuber LM, Wardle DA , Dorrepaal E (2023) Understory functional groups and fire history but not experimental warming drive tree seedling performance in unmanaged boreal forests. Front. For. Glob. Change, Sec. Temperate and Boreal Forests, Vol 6. doi.org/10.3389/ffgc.2023.1130532  

Wang Y, Lett S, Rousk K. (2022) Too much of a good thing? Inorganic nitrogen (N) inhibits moss-associated N2 fixation but organic N can promote it. Biogeochemisty. DOI:10.21203/rs.3.rs-1022519/v1

Rzepczynska AM, Michelsen A, Olsen MAN, Lett S (2022) Bryophyte species differ widely in their growth and N2-fixation responses to temperature. Arctic Science. https://doi.org/10.1139/as-2021-0053

Lett S, Jónsdóttir IS, Becker-Scarpitta A, Christiansen CT, During H, Ekelund F, Henry GHR, Lang SI, Michelsen A, Rousk K, Alatalo JM, Betway KR, Busca S, Callaghan T, Carbognani M, Cooper EJ, Cornelissen JHC, Dorrepaal E, Egelkraut D, Elumeeva TG, Haugum SV, Hollister RD, Jägerbrand AK, Keuper F, Klanderud K, Lévesque E, Liu X, May J, Michel P, Mörsdorf M, Petraglia A, Rixen C, Robroek BJM, Rzepczynska AM, Soudzilovskaia NA, Tolvanen A, Vandvik V, Volkov I, Volkova I, van Zuijlen K (2021) Can bryophyte groups increase functional resolution in tundra ecosystems? Arctic Science. doi.org/10.1139/AS-2020-0057

Lett S, Teuber L M, Krab E J, Michelsen A, Olofsson J, Nilsson, M-C, Wardle D, Dorrepaal E (2020) Mosses modify effects of warmer and wetter conditions on tree seedlings at the alpine treeline. Global Change Biology. 26(10), 5754-5766. DOI 10.1111/gcb15256

Lett S, Wardle D, Nilsson M-C, Teuber L, Dorrepaal E. (2018) The role of bryophytes for tree seedling responses to winter climate change: implications for the stress gradient hypothesis. Journal of Ecology. 106 (3), 1142-1155. DOI: 10.1111/1365-2745.12898

Lett S, Nilsson M-C, Wardle D, Dorrepaal E. (2017) Bryophyte traits explain climate-warming effects on tree seedling establishment. Journal of Ecology. 105 (2), 496-506. DOI: 10.1111/1365-2745.12688

Rousk K, Sorensen PL, Lett S, Michelsen A. (2014) Across-Habitat Comparison of Diazotroph Activity in the Subarctic. Microbial Ecology. 69 (4), 778-787. DOI: 10.1007/s00248-014-0534-y

Lett S, Michelsen A. (2014) Seasonal variation in nitrogen fixation and effects of climate change in a subarctic heath. Plant and Soil. 379 (1-2), 193-204.DOI: 10.1007/s11104-014-2031-y

Sorensen PL, Lett S, Michelsen A. (2012). Moss-specific changes in nitrogen fixation following two decades of warming, shading, and fertilizer addition. Plant Ecology. 213 (4) 695–706. DOI: 10.1007/s11258-012-0034-4