Kaia defended her PhD!

A general rise in air temperature damages plant photosynthesis. During a hot period, plants also emit an odour which indicates cellular damage, as is evident in a recently defended doctoral thesis by Kaia Kask.

Plants are susceptible to various abiotic factors during their growth, such as low and high temperatures, drought, and excess water and light. According to Kaia Kask, rising temperature is one of the most topical issues at this time, as it threatens the ecosystem as a whole.

Therefore, Kask decided to study plant species separately. She was interested in the effects of heat stress on the photosynthesis and volatile organic compound emissions in black mustard and tobacco.

“Both the black mustard and tobacco experienced strongly reduced stomatal conductance and negative carbon fixation at higher temperatures,” said Kask describing the results. According to her, this indicates extensive damage to the photosynthetic processes and the prevalence of respiration.

In the case of black mustard, heat stress caused the emissions of species-specific glucosinolate breakdown products together with green leaf volatiles. Both volatile groups indicate cellular damage.

Brassica nigra (pic from wiki)

At higher temperatures, tobacco also emitted similar green leaf volatiles. Furthermore, tobacco emitted other characteristic volatile compounds which indicate the increased heat stress it had to endure.

According to Kask, these results improve the understanding of species-specific responses of plant photosynthesis and volatile organic compound emissions. In particular, heat stress severity and type affect volatile organic compound emissions from the leaves.

“Volatile organic compounds play a key role in plant-plant, plant-insect and plant-insect-environment relationships,” added Kask.

The doctoral thesis defended at the Estonian University of Life Sciences can be found here.

The translation of this article from Estonian Public Broadcasting science news portal Novaator was funded by the European Regional Development Fund through Estonian Research Council.

Nicotiana tabacum (pic from wiki)

Articles in the thesis:

Kask K., Kännaste A. & Niinemets Ü. (2013) Emission of volatile organic compounds as a signal of plant stress. Scientific Bulletin of ESCORENA 8, 79–93.

Kask K., Kännaste A., Talts E., Copolovici L., Niinemets Ü. (2016) How specialized volatiles respond to chronic and shortterm physiological and shock heat stress in Brassica nigra. Plant, Cell and Environment 39, 2027–2042.

Turan S., Kask K., Kanagendran A., Li S., Anni R., Talts E., Rasulov B., Kännaste A., Niinemets Ü. (2019) Lethal heat stressdependent volatile emissions from tobacco leaves: what happens beyond the thermal edge? Journal of Experimental Botany, 70, Issue 18, 5017–5030.

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High School student made a research in the University of Life Sciences measuring volatile organic compound emissions in Brassica oleracea var sabellica

Text and pics by Urmas Tokko, Raffael Somelar, Kaia Kask

During the recent school year a student of Tartu Tamme Gymnasium (TTG), Raffael Somelar (11th Grade of nature science class), studied the effects of temperature rise and mechanical wounding on volatile organic compound emissions (VOCs) in kale (Brassica oleracea var. sabellica). The research was made by the supervision of Kaia Kask (PhD), specialist in the Institute of Agricultural and Environmental Sciences, and Urmas Tokko, teacher of biology in TTG. The cooperation between us was very good.

The student and the supervisors found the topic very interesting and promising in regards to better understanding the influence of climate changes in plant communities.

Lab work started in summer 2019, with planning and carrying out the experiments. Experiments were conducted with specialized equipment in the laboratory, which offered many new experiences. The main interest in this study was how the rate of VOCs emissions changes in young kale plants exposed to heat stress and mechanical wounding.

Kale under stress

The results were quite interesting, and in many cases went well together with the theoretical side. Comparisons with previously conducted research with different plants from the Brassicaceae family showed that kale does react slightly differently to heat stress. Moreover, mechanical wounding caused the nice bouquet of green leaf volatiles.

The defence of given research will take place at 25th of May 2020 in Tartu Tamme Gymnasium. The theme (plant stress, VOCs, etc) itself was very interesting to learn about for the participating student. Both the student and the school are very glad about the possibility to conduct an interesting scientific research with the help of its infrastructure and under the supervision of a good specialist, Kaia Kask. We would also like to thank Ü. Niinemets for providing this hands-on opportunity.

Raffael and Kaia
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New publication – The fate of carbon in a mature forest under carbon dioxide enrichment

Originally published in emu.ee site (link).

Nature: Don’t hope mature forests to soak up carbon dioxide emissions

Foto: Western Sydney University

Globally, forests act as a large carbon sink, absorbing a substantial portion of the anthropogenic CO2 emissions. Whether mature forests will remain carbon sinks into the future is of critical importance for aspirations to limit climate warming to no more than 1.5 °C above pre-industrial levels? Researchers at Western Sydney University’s EucFACE (Eucalyptus Free Air CO2 Enrichment, see the photo) experiment have found new evidence of limitations in the capacity of mature forests to translate rising atmospheric CO2 concentrations into additional plant growth and carbon storage. The unique experiment was carried out in collaboration with many scientist over the world. The Head of the Centre of Excellence EcolChange Professor Ülo Niinemets and senior researcher Astrid Kännaste from the Estonian University of Life Sciences have contributed to data collection and data analysis of this study.

Carbon dioxide (CO2) is sometimes described as “food for plants” as it is the key ingredient in plant photosynthesis. Experiments in which single trees and young, rapidly growing forests have been exposed to elevated CO2 concentrations have shown that plants use the extra carbon acquired through photosynthesis to grow faster.

However, scientists have long wondered whether mature native forests would be able to take advantage of the extra photosynthesis, given that the trees also need nutrients from the soil to grow. This question is particularly relevant for Australia. In the first experiment of its kind applied to a mature native forest, Western Sydney University researchers exposed a 90-year old eucalypt woodland to elevated CO2-levels. “Just as we expected, the trees took in about 12% more carbon under the enriched CO2 conditions,” said Distinguished Professor Belinda Medlyn. “However, the trees did not grow any faster, prompting the question ‘where did the carbon go?’”.

The researchers combined their measurements into a carbon budget that accounts for all the pathways of carbon into and out of the EucFACE forest ecosystem, through the trees, grasses, insects, soils and leaf litter. This carbon-tracking analysis showed that the extra carbon absorbed by the trees was quickly cycled through the soil and returned to the atmosphere, with around half the carbon being returned by the trees themselves, and half by fungi and bacteria in the soil. “The trees convert the absorbed carbon into sugars, but they can’t use those sugars to grow more, because they don’t have access to additional nutrients from the soil. Instead, they send the sugars below-ground where they ‘feed’ soil microbes”, explained Professor Medlyn.

These findings have global implications: models used to project future climate change, and impacts of climate change on plants and ecosystems, currently assume that mature forests will continue to absorb carbon over and above their current levels, acting as carbon sinks. Professor Niinemets said: “What did we find? Increased uptake by the forest in elevated CO2, but not increased retention of this extra C. Instead, the extra C that was taken up was released back to the atmosphere. The future emissions could mean worse outcomes than we thought in terms of future climate, given this lack of response by nutrient-limited mature forests.”

Reference: Jiang, M., Medlyn, B. E., Drake, J. E., Duursma, R. A., Anderson, I. C., Barton, C. V., … Kännaste, A.,Niinemets, Ü., … & Crous, K. Y. (2020). The fate of carbon in a mature forest under carbon dioxide enrichment. Nature, 580(7802), 227-231. (link to full text)


Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.

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Workgroup and EcolChange seminar – Collins about the intraspecific variability of potato disease in Russia

Seminar of Chair of Crop Science and Plant Biology and Centre of Excellence EcolChange, Estonian Univ of Life Sciences

Presenter: Collins Agho is a PhD-student in the Estonian University of Life Sciences

Title of talk: High genotypic and phenotypic diversity of Phytophthora infestans in Pskov region, North-West Russia

Time: Monday, 2. March 2020 at 12.00

Place: Tartu, Kreutzwaldi 5 – D267 (Metsamaja)

pic from here
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Workgroup and EcolChange seminar – Rajendra and Linda-Liisa about boreal tree VOCs and gymnosperm mesophyll

Seminar of Chair of Crop Science and Plant Biology and Centre of Excellence EcolChange, Estonian Univ of Life Sciences

This week we have a double featured seminar.

First presenter: Rajendra Prasad Ghimire is a postdoc in University of Eastern Finland, who is visiting scientist in our lab during this semester

Title of his talk: Biogenic VOC emissions from boreal trees – effects of biotic and abiotic stress factors

Second presenter: Linda-Liisa Veromann-Jürgenson is a PhD student in EMÜ.

Title of her talk: The anatomical basis of mesophyll conductance in gymnosperms

Time: Monday, 17. February 2020 at 12.00

Place: Tartu, Kreutzwaldi 5 – D143 (Metsamaja; “Aquarium room”)

Boreal forest in Verkhoyansk, Russia, where the winter temperatures are the coldest in the northern hemisphere (average January temperature -45 oC), and it holds the Guiness record for the greatest temperature range in the world – 105 oC (pic from wiki)
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New visiting researcher – welcome Rajendra

Profile created by Rajendra Ghimire

Rajendra Prasad Ghimire, PhD (a visiting researcher)

Workplace: University of Eastern Finland, Department of Environmental and Biological Sciences, Kuopio, Finland

Position: Post-doctoral researcher

Research area: Environmental ecology, plant ecology, phytochemistry and global change

Research works: studying chemical defence of conifer tree species in response to biotic and abiotic stress factors, understanding stress-induced volatile plant secondary compounds (PSCs) with the focus on biogenic volatile organic compounds (BVOCs) in conifer tree species, and evaluating PSC-mediated ecosystem feedbacks to climate change


  • Studied how insect herbivory (pine sawflies Neodiprion sertifer Geoffroy, Diprion pini L., and Acantholyda posticalis Matsumura and European spruce bark beetles Ips typographus L.) and climate change factors (warming, ozone and soil nitrogen availability) affect BVOC emissions from boreal conifers (Scots pine and Norway spruce).

Postdoc project

  • Studying the effects of fungal pathogen (Dothistroma septosporum) infection on BVOC profiles of Scots pine in Riistavesi forest site in Kuopio, Finland
  • Assessing the effects of warming and insect herbivory on BVOC emissions from a birch-dominated subarctic heath ecosystem in an open-field exposure site at Kevo Subarctic Research Station in Utsjoki, Finland

Current workplace (01.01.2020-30.06.2020):

Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Chair of Crop Science and Plant Biology (Head of the Chair: Prof. Ülo Niinemets), Tartu, Estonia

Current project aims:

  • To assess the effects of long-term warming on BVOC emissions and photosynthesis/CO2 uptake in young seedlings of two dominant conifer tree species (i.e. Norway spruce and Scots pine) in boreal forests.
  • To use the data collected in the modelling of BVOC emissions in the boreal forest region.
  • To publish a joint paper using data of this project in a collaboration with Prof. Niinemets’s lab (modelling collaborator: Dr. Steffen M. Noe)
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Workgroup and EcolChange seminar – Tana about the comparison of VOCs of living fossils and modern plants

Seminar of Chair of Crop Science and Plant Biology and Centre of Excellence EcolChange, Estonian Univ of Life Sciences

Presenter: Wuyuntana is a PhD-student in the Estonian University of Life Sciences.

Title of the talk: Comparison of the kinetics and magnitude of biogenic volatiles emission between “living fossil” Selaginella and “modern plant” Nicotiana

Time: Monday, 3. February 2020 at 12.00

Place: Tartu, Kreutzwaldi 5 – D143 (Metsamaja; “Aquarium room”)

Diversity of Selaginellas (pic from here)
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