New publication – Global patterns of biomass allocation in woody species with different tolerance of shade and drought: evidence for multiple strategies

Text by Giacomo Puglielli

Can we solve a long-standing debate in plant ecology?

Plants are known to allocate the greatest proportion of biomass to the organs involved in the acquisition of the most limiting resource for growth. For example, if light is limiting plant growth then plants are expected to allocate more biomass to aboveground parts (i.e. leaves and stems) and less to roots. Conversely, when soil water is the limiting factor, then biomass allocation to roots is expected to be greater compared to that allocated to aboveground parts. Such model is also known as Optimal Partitioning Theory (OPT), and its first formulation dates back to 1960s. OPT has been formulated and it is valid at the intraspecific level, when a single species is exposed to different environmental conditions.

Plant species inherently differ in their habitat affinity, so that there are species that consistently perform the best in shaded or in dry environments. A long-standing debate in plant ecology is if OPT predictions can equally apply when addressing interspecific differences in biomass allocation between species differing in their habitat affinity. Nevertheless, results are scattered and often not consistent across studies. The greatest limitations of previous studies are: i) the sample size (differences among few species from a single ecosystem type are evaluated); ii) the considered range of total plant biomass that strongly influences biomass allocation patterns. Also differences between plant functional types could have further blurred previous results.

We used the most extensive database of biomass allocation available for woody species (Poorter et al., 2015) spanning more than 10 orders of magnitude in plant size, and complemented it with information on species ecological tolerance of shade and drought (i.e. habitat affinity in response to light and water availability), and on plant functional type (deciduous and evergreen broad-leaf and evergreen needle-leaf). The final dataset included 7377 observations of biomass allocation to leaves, stems and roots spanning 604 species worldwide from tropical to boreal ecosystems. We used this dataset to test if OPT predictions are equally valid at the interspecific level independently of developmental stages and plant functional types.

The main and most novel result we obtained is that plant functional type is the major determinant of biomass allocation patterns independently of the considered tolerance. Ifanything, differences between tolerant and intolerant species often run in opposite directions compared to OPT predictions. Also the total plant size at which the comparison was made strongly influenced the observed differences. We conclude that the detection of a given difference between tolerant and intolerant species strongly depends on the size at which the comparison has been made within each plant functional type.

Biomass allocation fractions to: (a-c) leaves (LMF); (d-f) stems (SMF); and (g-i) roots (RMF) at different shade tolerance levels (1 = intolerant; 3 = tolerant) at three fixed values of total plant dry mass at which differences were evaluated (Seedlings = 0.001 Kg; Small trees = 10 kg; Big trees = 1000 kg) for deciduous broad-leaf species.(Figure is from the paper.)

In the paper we also discuss other determinants of biomass allocation patterns between tolerant and intolerant species at the global scale, namely changes in organ morphology together with phenotypic plasticity and the effect of plant architecture on biomass allocation. Altogether, such factors allow tolerant and intolerant woody species to display multiple biomass allocation strategies in response to shade and drought.

While we partly solved a long-standing debate in plant ecology we could not challenge another one, biological patterns are not as easy as theory suggests….luckily for us!

Citation: Puglielli, G., Laanisto, L., Poorter, H., & Niinemets, Ü. (2020). Global patterns of biomass allocation in woody species with different tolerance of shade and drought: evidence for multiple strategies. New Phytologist,


The optimal partitioning theory predicts that plants of a given species acclimate to different environments by allocating a larger proportion of biomass to the organs acquiring the most limiting resource. Are similar patterns found across species adapted to environments with contrasting levels of abiotic stress?

We tested the optimal partitioning theory by analysing how fractional biomass allocation to leaves, stems and roots differed between woody species with different tolerances of shade and drought in plants of different age and size (seedlings to mature trees) using a global dataset including 604 species.

No overarching biomass allocation patterns at different tolerance values across species were found. Biomass allocation varied among functional types as a result of phenological (deciduous vs evergreen broad‐leaved species) and broad phylogenetical (angiosperms vs gymnosperms) differences. Furthermore, the direction of biomass allocation responses between tolerant and intolerant species was often opposite to that predicted by the optimal partitioning theory.

We conclude that plant functional type is the major determinant of biomass allocation in woody species. We propose that interactions between plant functional type, ontogeny and species‐specific stress tolerance adaptations allow woody species with different shade and drought tolerances to display multiple biomass partitioning strategies.

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EcolChange seminar – Siim-Kaarel Sepp about soil biota and land use

Seminars of Department of Botany and Centre of Excellence EcolChange

Speaker: Siim-Kaarel Sepp is a PhD student at the Plant Ecology workgroup of our Department of Botany. His research focuses on mycorrhizal fungi, in particular the impact of land use on arbuscular mycorrhizal fungi. Siim-Kaarel Sepp will defend his PhD thesis in December.

Title of the talk: Responses of soil eukaryotic communities to land use and host identity

Time: Thursday, 22. October 2020 at 14.15

Place: Tartu, Lai 40-218 (Vaga auditorium), or virtual link in the MS Teams group.

Summary: Knowledge pertaining to diversity patterns of belowground organisms is piecemeal. On the one hand, we lack understanding of the behaviour of particular groups of organisms and the characteristics of the interactions they form. On the other hand, seldom are the effects of land use change studied on several groups in parallel. The presentation will shed light on correlated responses of belowground organisms and report the effects of human influence on a particularly important group of soil-dwelling microorganisms, the arbuscular mycorrhizal (AM) fungi. Further, we look at the properties of an AM interaction network and the implications of the revealed structure.

For everyone to stay as healthy as possible, please be reminded that wearing a face mask is mandatory. Please bring your own mask. Most importantly, don’t attend when you feel sick.

An early theoretical model of the density of soil biotic interactions. Every line represents one interaction. By Kazimir Malevich (pic from Wiki)
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EcolChange seminar – Marina Semchenko about plant-soil feedbacks

Seminars of Department of Botany and Centre of Excellence EcolChange

Speaker: Marina Semchenko is a senior researcher at our Department of Botany, in the Plant Ecology work group. Her main research focus is on biotic interactions between plants, including the role of root exudates and soil microbes in mediating plant-plant interactions, especially from an evolutionary point of view.

Title of the talk: Plant-soil feedbacks: current trends and known unknowns

Time: Thursday, 15. October 2020 at 14.15

Place: Tartu, Lai 40-218 (Vaga auditorium), or virtual link in the MS Teams group.

Summary: Environmental gradients and plant functional traits have been key to explaining local and global patterns of plant diversity and primary production. It is increasingly recognised that soil microorganisms also play a critical role in promoting plant species co-existence and regulating ecosystem functioning. Studies ranging from temperate grasslands to tropical forests suggest that these effects are driven by the accumulation of host-specific pathogenic fungi in soil and associated suppression of locally abundant plant species, a phenomenon known as negative plant-soil feedback. However, the identity and characteristics of pathogenic fungi involved in negative plant-soil feedback remain largely unknown, as do the links between plant-fungal interactions, plant traits and soil abiotic context.

For everyone to stay as healthy as possible, please be reminded that wearing a face mask is mandatory. Please bring your own mask. Most importantly, don’t attend when you feel sick.

Mugshot of the study object (pic from here)
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EcolChange seminar – Triin Reitalu about historical plant diversity analysis based on pollen data

Seminars of Department of Botany and Centre of Excellence EcolChange


Dr. Triin Reitalu is senior researcher at the Institute of Geology at Tallinn University of Technology. She works on the functional and phylogenetic diversity in sedimentary pollen and plant macrofossil data. Triin Reitalu was once a member of our Department during her bachelor and master studies as well as a research fellow and is still collaborating with colleagues from the Department.

Title of the talk: Reconstructing past plant diversity with the help of pollen data

Time: Thursday, 8. October 2020 at 14.15

Place: Tartu, Lai 40-218 (Vaga auditorium), or virtual link in the MS Teams group.

Summary: Pollen that is preserved in lake and mire sediments provides information about millennial-scale vegetation changes. Associations between pollen and plant data in current landscapes can be used to better understand the problems and possibilities in sediment pollen interpretation. Exploring different biodiversity indicators such as functional and phylogenetic diversity with the help of pollen data offers new perspectives on palaeoecological diversity reconstructions.

For everyone to stay as healthy as possible, please be reminded that wearing a face mask is mandatory. Please bring your own mask. Most importantly, don’t attend when you feel sick.

Pic from here
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New publication – Landscape context and plant population size affect morph frequencies in heterostylous Primula veris ‐ results of a nationwide citizen‐science campaign

Text and photos by Tsipe Aavik

Citizen scientists bring surprising insights into cowslip mating system

About half of the individuals of cowslip (Primula veris) have flowers with a short style, while the other half of individuals produce flowers with a long style. Recent discoveries have suggested that the loss and fragmentation of habitats may shake this optimal balance of morphologically different plants. This, in turn, decreases the reproductive success of plants and jeopardizes their future viability.

As the primary habitat, cowslips prefer semi-natural grasslands, which have experienced a dramatic area loss over the last hundred years throughout Europe. The study coordinated by the ecologists of the University of Tartu and the Estonian Fund for Nature aimed to examine whether this drastic landscape change has led to deviations in morph balance. To collect data across Estonia, they decided to implement a citizen science approach. A specifically designed web platform facilitated an easy upload of data. “In addition, the task and importance of the cowslip observation campaign were explained in detailed guidelines, numerous videos, social media, and other communication platforms,” commented Tsipe Aavik, the lead researcher of the heterostyly project.

Cowslip is a distylous species with two morphologically different types of flowers. Plants with short-styled or S-morphs (photo A; sometimes referred to as thrum plants) carry flowers with a short style and long anthers, while long-styled L-morphs (or pin plants; photo B) have a long style and short anthers. Generally, successful fertilization takes place only in case of reciprocal pollen flow between different morphs, while within-morph crosses lead to no progenies.

Novel insight into fundamental research

Nearly 1,700 observations obtained during the campaign led to unexpected discoveries, is now published in the Journal of Ecology. First, data revealed a systematic dominance of short-styled morphs over long-styled morphs. Second, morph frequencies were more likely to deviate in smaller populations and deviations increased in landscapes with higher human population density.

“We are very thankful to all participants who helped to collect heterostyly data at such an unprecedented scale,” commented Tsipe Aavik. “Although the first discoveries on heterostyly were made already by Darwin more than 150 years ago, data obtained in the citizen science campaign has helped us to add novel aspects into this fascinating topic with a long history of research.”

The findings brought novel insights into fundamental research: the systematic dominance of the short-styled morphs is an intriguing but previously undescribed aspect in this otherwise well-studied plant mating system. However, perhaps even more important are the implications of these findings for conservation because deviating morph frequencies are likely to jeopardize the viability of heterostylous plants. The findings thus describe another threat in the list of negative consequences of habitat loss.

Perhaps Europe could be looking for cowslips one day

The surprising findings of the study have seeded an idea to widen the geographic scope of the study to examine whether the observed patterns are confirmed in other European countries. Furthermore, the discovery about the role of human population density altering morph balance encourages to look at the patterns of heterostyly in landscapes with more intense human impact than Estonia with its relatively low human population density. “In the spring of 2020, when we repeated the campaign, Latvian citizen scientists warmly welcomed the opportunity to contribute to heterostyly observations. But perhaps one day we all can participate in a project ‘Europe is looking for cowslips’,” adds Aavik with a hope that there still are places in Europe where one can find this beautiful and intriguing plant, cowslip.

Citation: Aavik, T., Carmona, C. P., Träger, S., Kaldra, M., Reinula, I., Conti, E., … & Kaisel, M. Landscape context and plant population size affect morph frequencies in heterostylous Primula veris‐results of a nationwide citizen‐science campaign. Journal of Ecology,


  1. Heterostyly is a genetically determined floral polymorphism of style length promoting outcrossing between individuals of different morphs, which usually coexist within populations at equal frequencies. Loss in the area and connectivity of suitable habitats may cause deviations from the expected equal morph frequencies. However, there is a need to evaluate the generality of this pattern at larger spatial extents and to identify possible underlying mechanisms.
  2. A citizen‐science approach was used to study morph frequencies in populations of the heterostylous grassland plant Primula veris across Estonia. We developed an online platform to facilitate an easy upload of the data. We examined the effect of the following variables in the surroundings of the study populations reflecting the landscape context on the deviation of morph ratios: (a) semi‐natural grasslands, (b) forests and shrubs, (c) human population density and (d) a proxy for plant population size.
  3. The citizen‐science approach provided unprecedented density of data from 1,700 localities. Nearly half of these observations, which were maintained for further analysis after data filtering, included over 62,000 short‐styled morphs and about 54,000 long‐styled morphs. Small populations were characterized by higher overall deviation of morph ratios from isoplethy (equal morph ratio). Deviation increased in semi‐natural grasslands located in regions with high human population density.
  4. The significant effect of human population density and plant population size on deviations of morph frequencies suggests the role of stochastic demographic effects of habitat fragmentation on morph ratios. Overall lower proportion of long‐styled morphs indicates that partial intra‐morph compatibility shown in long‐styled morphs may lead to higher inbreeding and related decline in fitness and abundance.
  5. Synthesis. Citizen‐science data about the morph type of Primula veris across Estonia obtained with the help of thousands of people demonstrates that in addition to plant population size, landscape context may affect plant reproductive traits, such as heterostyly. Larger population size of P. veris can help to buffer against random fluctuations in this trait. Increasing impact of human activities may have a negative impact on both small and large populations. The exact underlying mechanisms of the prevalence of one morph over the other, however, pose novel questions for further research.

This post was originally published in EurekAlert (link)

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New publication – Contrasting co‐occurrence patterns of photobiont and cystobasidiomycete yeast associated with common epiphytic lichen species

Text by Lauri Laanisto

Spreading contingency on intimate relationships

The world of lichens seemed a pretty clear when I was a bachelor student of biology in late 90s. Pretty and clear, to be more precise. It´s difficult to like these strange creatures. Of course, we only studied species that could be identified with the eye or a little magnifying glass. All the species were in one book, and that was it.

A few years later things begun to get confusing. Suddenly appeared the term mycobiont and started dominating in lichen talk. There was no more symbiontic lichen – the holobiontic nature of this being was disentangled into two unequal parts. Fungus was the real deal, and algae (photobiont) was suddenly an outcast, marginal nobody hiding somewhere on the edge of the mycobiontic thallus. It was because sequencing came along. How do you identify the genetics of a symbiontic organism. You have scrap all but one of the partners.

The new system took a while, but we all got used to it. Identification in the field was based on the whole organism, and databases mainly used the genetics of the mycobiont.

But then came another blow by Spribille et al. Apparently the lichen was not so simple. There´s not just the fungus and algae – there is also some kind of shady yeast living in the lichen. Permanently. And very species-specifically, meaning that the the same myco-, photo-, and yeast biont species always lived together. Lichen became a conservative threesome, where all the partners are faithful and commited to a single thallus.

Our study, however, makes things more complicated. Sorry! Our analysis showed that mycobiont and photobiont are indeed basically always coupling up in the same combinations of species. But the yeast. That one is volatile. Sometimes it was one species living together with the same combination of myco- and photobiont, sometimes other. They were also taxonomically more variable than previously thought. We could not really put our finger to their distribution drivers. Our samples, collected by Kristiina, were from Estonia and Switzerland, showed completely different species (or OTUs, to be more precise) pool for these two countries. But why…

JH Lawton famously called community ecology collecting stamps. The same seems to be the case with lichens. It´s a symbiotic contingency. Once ecologists become interested in something, the contingency virus will spread and corrupt the pretty and clear systems established long time ago. This is why we cannot have nice things. Just ecology…

pic from here

Citation: Mark, K., Laanisto, L., Bueno, C. G., Niinemets, Ü., Keller, C., & Scheidegger, C. (2020). Contrasting co‐occurrence patterns of photobiont and cystobasidiomycete yeast associated with common epiphytic lichen species. New Phytologist, (link to full text)


The popular dual definition of lichen symbiosis is under question with recent findings of additional microbial partners living within the lichen body. Here we compare the distribution and co‐occurrence patterns of lichen photobiont and recently described secondary fungus (Cyphobasidiales yeast) to evaluate their dependency on lichen host fungus (mycobiont).

We sequenced the nuclear internal transcribed spacer (ITS) strands for mycobiont, photobiont, and yeast from six widespread northern hemisphere epiphytic lichen species collected from 25 sites in Switzerland and Estonia. Interaction network analyses and multivariate analyses were conducted on operational taxonomic units based on ITS sequence data.

Our study demonstrates the frequent presence of cystobasidiomycete yeasts in studied lichens and shows that they are much less mycobiont‐specific than the photobionts. Individuals of different lichen species growing on the same tree trunk consistently hosted the same or closely related mycobiont‐specific Trebouxia lineage over geographic distances while the cystobasidiomycete yeasts were unevenly distributed over the study area – contrasting communities were found between Estonia and Switzerland.

These results contradict previous findings of high mycobiont species specificity of Cyphobasidiales yeast at large geographic scales. Our results suggest that the yeast might not be as intimately associated with the symbiosis as is the photobiont.

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Why are Estonian mushroom scientists among the best in the world?

This post was originally written by Marian Männi and published in Research Estonia (link to the original post)


Estonian scientist Leho Tedersoo showing off his early spring mushroom haul. Photo credit: Leho Tedersoo

Estonia became the world’s centre of mycology against all odds.

Around every fifth person in Tartu, Estonia’s second largest city, is a student. The life revolves around the University of Tartu, one of the oldest universities in Northern and Eastern Europe, founded in 1632.

This small riverside town hosts some of the brightest minds in modern mycology, a scientific study of fungi. Fungi refers to organisms like molds, rusts, mildews, smuts, mushrooms, and yeasts.

Nine Estonian scientists were listed among the top 1% of most cited scientists in the world by Clarivate Analytics at the end of 2019. Other Baltic and Polish scientists combined are not as visible as Estonians.

Even more surprisingly, seven out of nine of those outstanding Estonian researchers – in one way or another – work in the field of mycology.

“You could say we are one of the centres of the world when it comes to mycology,” said Urmas Kõljalg, one of the most influential researchers listed.


Estonian mycologist Urmas Kõljalg discovering new species in the Chinese province of Yunnan. Photo credit: private collection

No doubt, Estonia now belongs to the ten percent of the most influential and efficient countries in the scientific world, said Jüri Allik, an Estonian scientist, who has been observing and analysing the Estonian scientists’ success story for years. Only a very few post-Soviet countries like Estonia and Georgia have achieved that.

Biology conference organisers want to raise the bar by including Estonian names on the speakers’ list. Scientists from all over the world ask them to review and correct their articles, so that the Estonian names could also be added as co-authors. This would increase their visibility and help them get published in higher-rated magazines.

“Everything is more amplified for us now,” said Leho Tedersoo, another top Estonian mycologist. “I get the most requests from Chinese scientists.”


Mycologist Leho Tedersoo receiving the Young Scientist Award from the president of Estonia, Toomas Hendrik Ilves, in 2016. Photo Credit: President Office of the Republic of Estonia

Staff at Arab universities want to hire them, so that the names of their institutions would appear next to the top published scientists’ names.

The scientific world is extremely competitive, but the Estonian mycologists stick together and support each other.

They were around four to five researchers and students, who used to meet in bars after work. Over the years, the group grew into around 20 fungi enthusiasts, who meet bi-weekly and share their knowledge and ideas.

“Of all the things, I am the proudest of, it is the little community we have created,” Kõljalg said.

Reaching the West during Soviet times

What makes this success story even more remarkable is that the local biologists survived the Soviet oppression of half a century, when there was pressure to publish scientific papers mainly in Russian, as English was forbidden and access to the top Western science was very limited.

And mycology is not a niche field by any means. Fungi are the second most species-rich organism group after insects. Their importance and visibility are growing fast as laboratories are looking for fossil fuel replacements. Creating bioplastics, biofuels, pharmaceuticals and other natural products requires fungi.

The study of fungi will become essential for future generations. It provides the most tangible hope for real change towards green economy.

Mushrooms hold the key to many secrets of nature.


Fungi bring us hope for the future. Photo credit: Renee Altrov

And Estonia’s story illustrates how top science can originate even under the most difficult circumstances against all odds.

The first scanty data on Estonian fungi were published in 1777, but the modern scientific mycology started in the middle of the deepest Soviet times by the “grand old man of mushrooms” Erast Parmasto.

He used Latin language to bypass the authorities and create connections with free world’s scientists. In 1968 he published a monograph in Latin titled “Conspectus Systematis Corticiacearum”. This defined a new group of fungi and worked like a spark in a haystack in the world of mycology. Western scientists were curious to know what was being done within the Soviet Union. Parmasto’s article provided a window into the hidden world.

Many scientists then reached out to him and he continued the correspondence for many years, often sharing the latest discoveries with his students before they were even published anywhere, as recalls his first PhD student, Urmas Kõljalg.

Parmasto travelled all over the Soviet Union to collect fungi. He created one of the largest collections of fungi in the whole of the Soviet Union in Tartu.

The love for nature and nationalism went hand in hand in Estonia. For instance, Lahemaa Rahvuspark, established in 1971 in Estonia, was the very first national park in all of the Soviet Union, despite the fact that the central government did not recognize the word “national”. Terms like “reservations” or “protected area” were preferred to “national park”. But Estonians insisted and overcame.

In the summer of 1989, a European Mycology Congress was held in Estonia. It was right around when the Baltic Way was formed. It was a unique human chain stretching from Tallinn to Vilnius where people held hands to show their desire for freedom. The international mycologists, who came to attend the congress, also joined the human chain.

An email address in the 1980s

Parmasto was a charismatic and extremely inspiring scientist who liked to spend most of his free time making observations in the forest. The current most cited mycologists – Urmas Kõljalg, Kessy Abarenkov and Leho Tedersoo come from a direct line of his teachings.

Parmasto knew another well-known academic – Endel Lippmaa, who arranged for him and his students to have personal computers. This was unheard of in the 1980s. Kõljalg still remembers his first Apple computer nowadays. He got his first email address by the end of the 80s, which was remarkable for the time, under the Soviet rule.

IT and mycology then got intertwined in Estonia and things really kicked off.

Estonia regained its freedom in 1991.

Kõljalg went to Gothenburg, Sweden to do his postdoctoral. He used some of his funding to purchase laboratory equipment and brought them with him back to Estonia in bags. His students could use the Swedish laboratories where they sent the samples.

The next generation was coming up. Around the change of the century, when Tedersoo came to study mycology, molecular methods were implemented.

The first DNA-based digital database was created that later grew into UNITE, which is now one of the best-known databases for fungi, and used by top mushroom scientists all over the world. Most users come from China, the US, Japan, Germany and the UK. After almost twenty years of work, Kõljalg and Abarenkov received Estonia’s most prestigious science award this year for their work.

Databases matter in mycology. There are around four to five million species of fungi in the world and over 90 percent is still not described. How can we develop something if we don’t know enough about it? This database aims to fill the gap and map all the fungi in the world.


There are around four to five million species of fungi in the world. Photo credit: Karl Ander Adami

Poor in networking, strong in concentration

It’s difficult to get published in the world’s best scientific magazines and many scientists don’t even try. It’s often a matter of confidence and networking, Tedersoo said, but also knowing the right keywords and people. Estonian mycologists are not good with small talk, but they make up for it with their concentration and IT skills.

“I’m good at virtual networking,” Tedersoo said jokingly.

He is also quite fearless when it comes to collecting samples.

In 2007, he showed how green plants can steal energy with the help of mushrooms. This was a change of paradigm for mycology. In 2014, Tedersoo published a global research for which he spent a year travelling the world, collecting mushrooms. It was published in Science and revealed the staggering and previously unknown diversity of species.

Tedersoo risked his life to get this article published. In Northern Brazil, he ended up in a mafia-controlled area where the police stopped him. That’s why Tedersoo always carries a roll of toilet paper and binoculars with him to have as an excuse for stopping by the road in case authorities question him. The story of being a fungi scientist may not sound believable enough.


It’s sometimes difficult to explain to the local authorities what he is doing alone in a forest when Tedersoo collects his samples. Photo credit: Kristi Pärn

Being amongst leading scientists is like being a top athlete. “It’s about constant training, competition and pushing your limits,” Tedersoo said.

The hard work has certainly paid off.

This article was funded by the European Regional Development Fund through Estonian Research Council.

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

Originally published in site (link).


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


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)


Foto: Western Sydney University


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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EcolChange seminar – Silvia Lotman about everyman´s right to care about nature

Seminars of Department of Botany and Centre of Excellence EcolChange

Speaker: Silvia Lotman is nature conservation expert and chairman of the board of the Estonian Fund for Nature (ELF). She studied in the Department of Botany, University of Tartu, and is now also the head of the species conservation program at ELF and leader of the LIFE project “NaturallyEST”.

Title of the talk: Estonian Fund for Nature and everyones’ nature conservation

Time: Thursday, 5. March 2020 at 14.15

Place: Tartu, Lai 40-218 (Vaga auditorium)

Summary: Silvia will give an overview of Estonian Fund for Natures’ strategic plan for nature conservation and the past, current and future plans for citizen science and everyones´ nature conservation projects.


Rights and obligations – everyman´s trade-off (pic from here)


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New publication – Population-level performance of Arabidopsis thaliana (L.) Heynh in dense monocultures

Text and pics by Susanna Vain

The tiny weedy species Arabidopsis thaliana can teach us quite a bit about agriculture, even though the species itself is not agriculturally important. Arabidopsis has played an immense role in helping us understand the molecular and/or genetic mechanisms behind plant functioning. Many such parallels have also been found in crops, hence the importance of Arabidopsis for agriculture.[1] In this particular study we were interested in using Arabidopsis to study competition on a population-level and its effects on seed yield, which is also something that could help us advance agriculture.

Plant breeding so far has focused on individual performance of plants, i.e. the best-performing individuals are selected. Farmers, however, do not pick out the best individuals, they are interested in the yield from the whole field where there are tens of thousands of plants, all growing and interacting together. This has brought discussion to alternatives – perhaps plant breeding should use group selection in which not best individuals but best groups are selected for further trials.[2] This method centers around the collective performance of plants and puts much greater emphasis on plant-plant interactions. Still, there are great gaps in our knowledge about plant-plant interactions, especially on a population-level scale.

Susanna arabidopsis 01

In this paper, the effect of plant density in two different photoperiod conditions was studied to learn how it affects the collective performance of plants. Plants were sown at five densities (17.6, 8.8, 4.4, 2.2 and 1.1 cm2 per plant) and grown either in 16 h or 12 h day length conditions. What is also relatively novel about the methodology of this experiment was that instead of small pots, quite large trays were used (44×25 cm). This ensured truer monoculture conditions – one sown population constituted minimum of 64 plants in the sparsest and 1000 plants in the densest treatment.

Surprisingly, populations across all sowing densities attained constant seed yield, which was greater for plants that grew in 16 h photoperiod treatment. This means that regardless of whether there were 64 plants, 500 or 1000 plants in a tray within a photoperiod treatment, all populations produced the same amount of seeds. Furthermore, no main effect of photoperiod treatment was found for vegetative biomass production. So, seemingly, differences in biotic and abiotic conditions did not trigger competitive responses which is usually indicated by differential biomass production (and that could have led to reduced yield as well).

Susanna arabidopsis 02

Did plants just make use of resources available to them, not minding their co-competitors at all? Not quite. Even though we found no evidence of differential vegetative biomass production, closer inspection revealed a sowing density and photoperiod treatment interaction for the average mass of 100 seeds. Plants that grew sparsely, produced seeds of similar weights in both photoperiod conditions. When sowing density was increased, the weight of individual seeds diverged in opposite directions – the average seed produced in 16 h conditions was heavier than that produced in 12 h photoperiod conditions. So, instead of varying vegetative biomass production, plants’ focus seemed to be on the seeds, which is not unexpected since Arabidopsis is a species with relatively short life-cycle (approx. 6 weeks).

In conclusion, this study showed that vegetative biomass and total seed yield are not the only things to consider when assessing the performance of plants. When plants produce the same amount of vegetative or generative biomass, then this does not automatically mean that plants have no reactions to different conditions at all. There is still a lot to be learned.

Susanna arabidopsis 03

Citation: Vain, S., Gielen, I., Liira, J., & Zobel, K. (2020). Population-level performance of Arabidopsis thaliana (L.) Heynh in dense monocultures. Journal of Plant Ecology, rtaa006, (link to full text)



Very little is known about the performance of non-agricultural plant species in monocultures, even though nearly all agricultural species have experienced the transition from multi-species environments to dense monospecific stands during the breeding process. In the light of recent work that highlighted the possibility that the weedy species Arabidopsis thaliana can offer novel insight into crop breeding, we aimed to test the effect of sowing density on group and individual performance in different photoperiod environments in A. thaliana.


We studied the performance of A. thaliana Cvi-0 ecotype. The choice of Cvi-0 was based on a preliminary experiment in which plants of Cvi-0 ecotype exhibited high competitive performance. Sowing densities used were 17.6, 8.8, 4.4, 2.2 and 1.1 cm2 per plant and photoperiod environments 12 h or 16 h of day light.


In this experiment, populations attained constant total seed yield for all densities. Some interaction effect occurred, as at high sowing density and at longer day length plants produced heavier seeds, whereas at shorter day length seed weight was negatively related to plant density. These results shed light on different strategies that annual plants can adopt when they face intense intraspecific competition, and could help to offer new perspectives for breeding crops with enhanced group performance.



[1] Gonzalez, N., Beemster, G. T., & Inzé, D. (2009). David and Goliath: What can the tiny weed Arabidopsis teach us to improve biomass production in crops? Current Opinion in Plant Biology, 12(2), 157–164.
[2] Weiner, J., Andersen, S. B., Wille, W. K.-M., Griepentrog, H. W., & Olsen, J. M. (2010). Evolutionary Agroecology: The potential for cooperative, high density, weed-suppressing cereals. Evolutionary Applications, 3(5–6), 473–479.
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