Always fascinated by microbes, Tinkara Bizjak-Johansson investigated bacterial and fungal communities in boreal forests during her PhD in Annika Nordin's research group (photo: Anne Honsel).
Microbes like bacteria and fungi are all around us, yet we rarely notice them. Tinkara Bizjak-Johansson studied microbial communities in boreal forests and showed that fertilisation shifts fungal community composition in the soil but does not affect nitrogen-fixing bacteria in conifer needles.
- You studied fungal and bacterial microbiomes in boreal forests during your PhD in Annika Nordin’s research group. What aroused your interest in this topic?
I have always thought that bacteria were fascinating because they are present everywhere, but we are not really aware of them. And even though we cannot see them as they are so tiny, they can cause big problems through certain diseases. The same counts for fungi. We do notice the ones in the forests that one can pick but those are just a few. There are so many more. Once I met Annika, we both got intrigued by the idea that there could be nitrogen-fixing bacteria present in the conifer needles. It is such an interesting place for nitrogen-fixing bacteria and not a lot was known about those communities at all. So, it kind of started with that question and then it developed further. The more research I did, the more questions arose.
- What are microbiomes and why are they important for forest ecosystems?
Microbiomes are communities of bacteria, fungi, Archaea, algae and small protists but I only focused on the bacteria and fungi. Those are the two groups that are mostly researched even though I think also the other groups are very interesting. Fungi and bacteria are important for forest ecosystems because they influence for example nitrogen and carbon cycling, plant nutrient availability and they are also, of course, affecting plant health in both negative and positive ways - even though we mostly notice the negative ways.
- When summarising your thesis, what do you consider as the major outcome?
I think that we can now better describe the boreal forest microbiome compositions and better understand the tree species effect on their composition. My thesis, additionally, focused quite a lot on how inorganic nitrogen addition can change these microbiomes. If nitrogen has been added to the forest over several years, the relative abundance of fungal species changed significantly compared to a non-fertilised control. Consequently, also the activity of their extracellular enzymes changed with the change in the fungal community. These enzymes are connected to nitrogen, carbon or phosphorus acquisition and facilitate for example litter decomposition in the boreal forests.
- Were there any results that you did not expect or that were astonishing you?
When looking at the nitrogen-fixing bacteria in conifer needles with and without nitrogen addition, we did not see any changes. They were still the same in both their abundance and their nitrogen fixation enzyme activity even though the forest has been fertilised for a very long time with added nitrogen. This was a quite surprising result! We expected that the nitrogen fixation enzyme activity would decrease because you see that for example for the mosses growing at the same field site. Their nitrogen fixation in association with cyanobacteria severely decreased with nitrogen addition. So, we were quite astounded that it was not the same for the ones sitting in the needles.
- Doing a PhD is often very challenging. Would you like to share some of the challenges that you had to overcome?
One of the laboratory challenges was that I was more interested in the endophytic microorganisms, meaning those that are sitting inside the plant tissues without causing disease symptoms. It was incredibly challenging to try to sterilise the material without killing all the microbes that were inside the needles as all the sterilisation solutions also go through the plant material. I spent a lot of time just figuring out how exactly I could do the sterilisation so that I really made sure that I was only looking at the endophytic microorganisms, but that I was not killing all of them. That was a lot of work before even starting the experiments that were part of my thesis.
- What are your plans now after finishing your PhD?
Even though I really enjoyed the research and working in academia, I plan to transition to the industry. I will start my new job in the industry soon after my defence, and work as a laboratory engineer. I think the seminar series “Outside of Academia” that Laura Tünnermann and I were organising was a nice way to discover what possibilities are out there in the industry. We got a good overview of potential career options, and it was inspiring to try to find an interesting position. I do like to work in the lab, and I missed that a bit in the last year when I have been mostly writing. So, I am excited to try out how it is to work in the industry.
About the PhD thesis:
Tinkara Bizjak-Johansson, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences (SLU), will defend her PhD thesis with the title “Some aspects on boreal forest microbiotas and nitrogen” at SLU on June 5, 2025. Faculty opponent will be A. Carolin Frank, Environmental Sciences group, University of California, Merced, USA. The thesis was supervised by Annika Nordin.
Link to Tinkara Bizjak-Johansson’s PhD thesis
For more information, please contact:
Tinkara Bizjak-Johansson, Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences
Email: