Workgroup and EcolChange seminar – Linda-Liisa Veromann-Jürgenson about mesophyll conductance in gymnosperms

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

Linda-Liisa Veromann-Jürgenson is a junior researcher and PhD-student in Estonian University of Life Sciences.

Title of the talk: Mesophyll conductance in gymnosperms: causes and consequences

Time: Wednesday, 06. December 2017 at 9.00

Place: Tartu, Kreutzwaldi 5 – D-143 (Metsamaja, Aquarium-room)


Mechanized flow through a gymnosperm tree (Wawona tree; pic from here)

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New papers published – Chemical stress and environmental feedbacks in aquatic ecosystems

Text by Lauri Laanisto

Ülo and his colleagues – this time mainly from Estonia – have published two subsequent papers in journal Regional Environmental Change. Both deal with more or less similar topic, and both are actually review papers.

The first paper emphasizes that we have so far quite limited knowledge regarding the effects and co-effects of abiotic stress and climate change in aquatic systems. We have some ideas by now, how these interactions change the productivity, diversity and other crucial characteristics of terrestrial ecosystems, but it is rather difficult or even impossible to extrapolate these ideas on aquatic communities.

The second paper takes the next step and tries to give an overview of potential mechanisms, feedbacks and feedback loops that one has to keep in mind, when starting to study the interactions mentioned in the paragraph above.

Both reviews have considerable length and they contain numerous schemes that provide fundamental framework how to approach research in this area.


Anthropogenic stress in aquatic ecosystem (pic from here)

Citation 1: Niinemets, Ü., Kahru, A., Mander, Ü., Nõges, P., Nõges, T., Tuvikene, A., & Vasemägi, A. (2017). Interacting environmental and chemical stresses under global change in temperate aquatic ecosystems: stress responses, adaptation, and scaling. Regional Environmental Change, 17(7), 2061–2077. (link to full paper)


Unfavorable environmental conditions—abiotic stress—constitute one of the key drivers of evolution leading to environmental adaptation. Since the start of industrial revolution, natural populations are also facing a new stress—global warming—that, in turn, leads to alteration of the severity of most of the existing stress factors and emergence of novel stress combinations. Biological adaptation to environmental perturbations occurs at all levels of biological organization, but the current knowledge on the role of adaptation in responses of ecosystems to global change is limited, especially concerning the interplay of climatic and chemical/pollutant stressors. Particularly limited is the understanding of how biological adaptation alters the performance of aquatic ecosystems that integrate the pollution and nutrient loads from large catchment areas. This review describes the responses, tolerance, acclimation, and adaptation of species at different levels of aquatic food chain to globally changing environmental drivers with emphasis on arctic to temperate ecosystems. The analysis highlights major variations in tolerance and in extent and speed of acclimation and adaptation to various environmental drivers within and among species and among species groups at different trophic levels. The variety of responses to novel stressors causes modifications in species composition and diversity and can lead to asynchronous peak activities of organisms at different trophic levels. All these effects are expected to profoundly alter the aquatic ecosystem productivity, resilience, and adaptation capacity and can ultimately modify the global feedbacks between ecosystem-level processes and environmental drivers. We argue that joint efforts of researchers working at different levels of biological organization are needed to understand and predict global change effects on various functional types of organisms and scale up from physiological responses to large-scale integrated ecosystem responses in future climates.


Citation 2: Niinemets, Ü., Kahru, A., Nõges, P., Tuvikene, A., Vasemägi, A., Mander, Ü., & Nõges, T. (2017). Environmental feedbacks in temperate aquatic ecosystems under global change: why do we need to consider chemical stressors?. Regional Environmental Change, 17(7), 2079–2096. (link to full paper)


Globally increasing temperature and modifications in precipitation patterns induce major environmental alterations in aquatic ecosystems. Particularly profound changes are predicted for arctic to temperate shallow lakes where modifications in temperature affect the distribution of ice and ice-free periods, thereby altering the timing of peak productivity, while changes in precipitation strongly alter water table depth with concomitant modifications in light distribution, temperature, and water chemistry, collectively altering the balance between primary production, organic matter consumption, and decomposition. Due to direct effects of temperature on primary productivity and microbial decomposition, raising temperatures alter the capacity of aquatic ecosystems for carbon sequestration and greenhouse gas release, and this affects atmospheric greenhouse gas concentrations and temperature, implying a feedback loop between environmental effects on ecosystems and climate change. Moreover, elevated temperature can modify the bioavailability of pollutants deposited in the past, and increase the probability for their uptake by aquatic organisms. The latter processes in turn reduce primary productivity and alter microbial decomposition, creating thus another key feedback loop between productivity, climate change, and environmental pollutants. However, warming can also enhance eutrophication and deposition of pollutants in organic sediments, further speeding up productivity and eutrophication, with the overall net effects depending on the quantitative significance of different processes. Therefore, the feedbacks arising from pollution stress must be incorporated in models intending to predict the carbon balance of aquatic ecosystems under globally changing environmental conditions. Further work on carbon balance and greenhouse gas release of aquatic ecosystems should focus on quantitative characterization of the feedback loops operative, and on how global change affects these feedback loops.


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Workgroup and EcolChange seminar – Chicodinaka N. Okereke about VOCs and abiotic stress in tropical plants

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

Chicodinaka N. Okereke is a junior researcher and PhD-student in Estonian University of Life Sciences.

Title of the talk: Volatile Organic Compounds (VOCs) induced by abiotic stress in tropical plants (Carica papaya L., Amaranthus hybridus L., A. cruentus L, Abelmoschus esculentus L., Telfairia occidentalis L. etc.)

Time: Wednesday, 08. November 2017 at 9.00

Place: Tartu, Kreutzwaldi 5 – D-143 (Metsamaja, Aquarium-room)


Pile of fluted pumpkins (Telfairia occidentalis). Happy fluted Halloween! (pic from here)


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Workgroup and EcolChange seminar – Shuai Li about the role of stomatal conductance in controlling various leaf processes

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

Shuai Li is a junior researcher and PhD-student in Estonian University of Life Sciences.

Title of the talk: Key role of stomatal conductance in controlling ozone uptake, leaf injury and volatile release

Time: Wednesday, 25. October 2017 at 9.00

Place: Tartu, Kreutzwaldi 5 – D-143 (Metsamaja, Aquarium-room)


Stoma! (pic from here)

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New paper published – Changes of secondary metabolites in Pinus sylvestris L. needles under increasing soil water deficit

Text by Lauri Laanisto

Together with Spanish colleagues, Ülo has published a study about how Scots pine´s primary and secondary metabolism in the needles changes when the tree is experiencing water deficit in soil. Frome the methodoligical point of view it is a rather run-of-the-mill small-scale study concentrating on a single stress factor in one species. Pretty self-explanatory stuff. Though, note the fact that the authors are also describing different phases of the response process, which is something that is not so common.

Such studies could be (or rather will be) vital for eventually drawing more comprehensive conclusions about how plants react to different stress factors. If you could put together 100+ of such studies, it could result in a pretty seminal meta-analysis (I am after all a macroecologist…). However, conducting such meta-analysis is currently not possible. Because such studies are actually not very abundant. We do not yet know the fundamentals in this fundamental area of research! Which for me is a quite convincing argument for publishing this kind of research.

Citation: Sancho-Knapik, D., Sanz, M. Á., Peguero-Pina, J. J., Niinemets, Ü., & Gil-Pelegrín, E. (2017). Changes of secondary metabolites in Pinus sylvestris L. needles under increasing soil water deficit. Annals of Forest Science, 74(1), 24. (link to full text)


A dying Scots pine in southern France following the 2003 European heat wave and drought (pic from here)


Key message

A multiphasic response to water deficit was found in Scots pine primary and secondary metabolism. First, an increase of terpenoids coincided with the stomatal closure. Second, an accumulation of proline, ABA, and shikimic acid was detected when photosynthesis was negligible.


Drought-induced mortality is characterized by a major needle yellowing followed by severe defoliation and whole branch death. Before these external visual symptoms of drought stress take place, different alterations occur in plant metabolism.


This study aims to detect changes in primary and secondary metabolism of Pinus sylvestris L. in response to a decrease in soil water availability.


We analyzed needle water potential, photosynthetic characteristics, and concentrations of proline, terpenoids, shikimic acid, total polyphenols, and abscisic acid (ABA) in P. sylvestris through a 55-day soil water deficit period.


Concentrations of most metabolites varied with the decrease in soil water availability, but changes in different compounds were triggered at different times, highlighting a multiphasic response. Increases in monoterpene and sesquiterpenoid content at moderate water deficit coincided with stomatal closure which preceded the accumulation of proline, ABA, and shikimic acid under severe water deficit when net photosynthesis was negligible.


This work confirms that most of the secondary metabolites under investigation in Pinus sylvestris did not increase until a moderate to severe water deficit was experienced, when photosynthesis was limited by stomatal closure.

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Guest post – Hannes Kollist about the emperor´s new clothes

Text by Hannes Kollist

<From the editor: Our good colleague Hannes Kollist, professor of Molecular Plant Biology and the PI of Plant Signal Research Group at University of Tartu, participated recently in EU high-level conference “Modern Biotechnologies in Agriculture – Paving the way for responsible innovation” and wrote down some of his reflections from that meeting. This text was originally published in the EU´s parliament magazine The Parliament (link to the original text).>


Hannes Kollist (pic from here)

The Emperor’s new clothes

It’s neither wise nor safe for EU policymakers to dismiss new breeding techniques as ‘dangerous’ without any real consideration of the facts, argues Hannes Kollist.

Hans Christian Andersen’s celebrated tale has served as an admirable metaphor for deception since its publication in 1837. It tells the tale of an Emperor who unknowingly parades naked before his subjects in a new suit of imaginary clothes sold to him by two swindlers. The truth is only revealed after a small child cries out, “But he has nothing on.” The recent EU high-level conference on “Modern Biotechnologies in Agriculture – Paving the way for responsible innovation”, highlighted that 180 years on from Andersen’s classic tale, deception remains rampant.

EU Commissioner for Health and Food Safety, Vytenis Andriukaitis called the meeting to discuss whether new breeding techniques (NBTs) should be classified as conventional, and accordingly be left out from those regulations that are in force for genetically modified (GM) plants. We are talking about recently developed methods that enable controlled and precise gene-editing and have been already used to give plants desired properties, similarly to those encountered throughout evolution.

There is a major difference between NBTs and GM methods. Many of these techniques do not introduce foreign DNA and often the resulting organisms have just a single nucleotide change to their DNA sequence: something that readily happens every time a DNA strand is naturally replicated.

New gene editing technologies are already revolutionising every field in life sciences, from plant breeding to human medicine. Obviously, these technologies will be effectively used in plant breeding and benefit in finding ways to boost nutritious plant growth while helping to minimise pesticide use, thus perfectly assisting organic farming objectives.

But instead of discussing the conference’s agenda, roughly 300 respected experts gathered and spent an entire day discussing unproven risks and the need for labelling organisms where NBTs are applied.

One of the priorities of the Estonian Presidency of the European Union is the development of an open and innovative economy. And I was proud to listen to the welcome speech given by Estonia’s rural affairs minister Tarmo Tamm, where he clearly stated that in addition to conventional breeding, the EU needs research-based solutions that have the potential to speed up breeding in a sustainable manner.

It would not be wise nor would it keep anyone more safe if these new technologies are brushed off as ‘dangerous’ without any real consideration.

Nevertheless, we spent the day in Brussels discussing scientifically unproven myths and legends concerning GM plants and NBTs. “There is no monopoly for being green”, Andriukaitis said to a Greenpeace representative at the meeting. I fully agree, I am ‘green’ as well, whenever possible I eat local unprocessed food, I am a hobby shepherd, and I am convinced that biodiversity is something we should be concerned about, as it’s vital to mankind’s sustainable development.

However, concerning the campaign against NBTs there is no doubt that this is one of the biggest public lies currently circulating and I simply do not understand how it is possible that despite all the facts 300 experts gathered in Brussels and no one dared to say that the Emperor was actually naked.

We should consider whether we want Europe to become a History Theme Park show-casing a “Museum of Agriculture” or whether we should aim to increase Europe’s competitiveness and be part of the next green revolution, possibly triggered by new innovative plant breeding techniques that will be a key component of sustainable development.

The EU and its institutions are perhaps the best possible platform that can be used to achieve this.

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New paper published – Physiological and structural tradeoffs underlying the leaf economics spectrum

Text and graph by Tiina Tosens

In the world-wide leaf economics spectrum (Wright et al. 2004, Nature) variability of three key traits: photosynthesis rate, leaf nitrogen content, and leaf dry mass per area of 2500 species (from study sites with highly variable mean annual humidity and temperature) fall along the single axis of this three-trait space. However, the striking question has been what actually is the parameter that drives LES relationships. Meta-analysis (lead by Dr. Yusuke Onoda from Kyoto University) confirms the speculations that this variation is caused by variable mesophyll conductance (e.g. CO2 diffusion efficiency from sub-stomatal cavities to chloroplasts) and different life strategies in terms of nitrogen investment into structural cell wall material rather than photosynthetic biochemistry (see the figure below).

onoda et al 2017 joonis Tiinalt

Illustration of structure-function relationships of two species with contrasting life strategies. Left: temperate decidous pioneer species Populus tremula and right side: evergreen Cycas taitungensis. Mesophyll tissue, epidermis, scleroids and cuticle are shown. Populus tremula leaf is positioned to fast return end of LES.  Populus invests  proportionally less resources into protective cells (scleroids, cuticle, thick mesophyll  cell walls) rather it invests into building 2 layers of thick physiologically active palisade tissue this in turn brings to high photosynthesis and fast growth rate while Cycads have proportionally more C and N invested into protective structural cells and therefore lower photosynthesis and slower growth rate. However, in longer perspective Cycas has longer leaf life span and slower energy return. That is, more nitrogen invested into cell walls means more durable and tougher leaves. On the other hand thick mesophyll cell walls represent longer liquid phase distance through cell walls (low mesophyll conductance) into the chloroplasts and therefore less efficient photosynthesis


Citation: Onoda, Y., Wright, I. J., Evans, J. R., Hikosaka, K., Kitajima, K., Niinemets, Ü., Poorter, H., Tosens, T. & Westoby, M. (2017). Physiological and structural tradeoffs underlying the leaf economics spectrum. New Phytologist, 214(4), 1447-1463. (link to full text)

Check also out a commentary titled “Peeking beneath the hood of the leaf economics spectrum” by by Reich and Flores-Moreno (link to full text) who emphasize the significance of this study: “What is most novel about their study is the bringing together of considerable data on rarely measured leaf traits, assessing both chemical (e.g. nitrogen (N) allocation) and diffusive (mesophyll conductance) constraints at the same time, and identifying a key role for cell-wall thickness in both of these.


  • The leaf economics spectrum (LES) represents a suite of intercorrelated leaf traits concerning construction costs per unit leaf area, nutrient concentrations, and rates of carbon fixation and tissue turnover. Although broad trade-offs among leaf structural and physiological traits have been demonstrated, we still do not have a comprehensive view of the fundamental constraints underlying the LES trade-offs.
  • Here, we investigated physiological and structural mechanisms underpinning the LES by analysing a novel data compilation incorporating rarely considered traits such as the dry mass fraction in cell walls, nitrogen allocation, mesophyll CO2 diffusion and associated anatomical traits for hundreds of species covering major growth forms.
  • The analysis demonstrates that cell wall constituents are major components of leaf dry mass (18–70%), especially in leaves with high leaf mass per unit area (LMA) and long lifespan. A greater fraction of leaf mass in cell walls is typically associated with a lower fraction of leaf nitrogen (N) invested in photosynthetic proteins; and lower within-leaf CO2 diffusion rates, as a result of thicker mesophyll cell walls.
  • The costs associated with greater investments in cell walls underpin the LES: long leaf lifespans are achieved via higher LMA and in turn by higher cell wall mass fraction, but this inevitably reduces the efficiency of photosynthesis.
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