Light after Death: Marta Pieristè’s PhD defence

Marta Pieristè successfully defended her PhD dissertation, “Light after Death: the importance of spectral composition in litter decomposition processes” on Tuesday 16th June 2020 at 10:30 a.m. EET Finland.  You can relive the PhD defence using the following video linkMarta Pieristè PhD defence

In addition to the Thesis Summary, the dissertation is composed of three published papers and one manuscript below:

  • Pieristè Neimane et al. (2020) Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of leaf litter from forest stands in southern Finland. Plant Physiology and Biochemistry. PLAPHY5920 146, 42–54.
  • Pieristè et al., (2019) Solar UV-A radiation and blue light enhance tree leaf litter decomposition in a temperate forest by accelerating photodegradation rate. Oecologia, 191(1), 191-203.
  • Pieristè et al., (2020) Sunlight affects the microbial functional structure of beech leaf litter. Plant & Soil,
  • Pieristè et al., (manuscript – embargoed) The crucial role of blue light as a driver of photodegradation in terrestrial ecosystems on the global scale: a meta-analysis.
Litter-boxes in the beech forest during the decomposition experiment in Rouen.

As a joint PhD between Normandie Universite Rouen and the University of Helsinki, Marta’s Examination was be conducted by:

Opponents: Prof Laura Llorens Guasch, University of Girona (Spain) and Dr Stephan Hättenschwiler, CNRS Montpelier (France).

Pre-examiners:  Prof Christiane Gallet, University Savoie (France) and Dr Tarja Lehto, University of Eastern Finland (Finland).

Custos : Prof Kurt Fagerstedt, University of Helsinki (Finland).

President: Prof Matty Berg, Vrije Universiteit Amsterdam (The Netherlands).

To meet the requirements of the co-tutelle PhD, the defence commenced with a 50 minute presentation – followed by 20-30 minutes of questioning by each examiner in turn.

UNEP EEAP 2019 Update published

The 2019 Update on the 2018 Quadrennial Assessment by the UNEP Environmental Effects Panel assessing how climate change, ozone and UV-B radiation interact is now published in Photochemical & Photobiological Sciences.

Bernhard et al., (2020), Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019. Photochemical & Photobiological Sciences DOI: 10.1039/d0pp90011g

The Panel met in Alexandria on the South Island of New Zealand in September-October 2019 to consider the latest research into these effects on climate, human health, terrestrial and aquatic ecosystem, materials, pollution, and biogeochemical cycling; as well as cross-cutting factors affecting all of these global concerns.

This year 2020, we will reconvene in September to consider what has been a very unusual year for ozone depletion and climate interactions in both the northern and southern hemispheres.

Sunset over Shoal Bay, New South Wales, Australia (Photo: Scott Byrne).

Craig Brelsford PhD Defence: Light quality affects leaf pigments and leaf phenology

Craig Brelsford from the CanSEE group at the University of Helsinki will defend his PhD dissertation entitled, “Light quality affects leaf pigments and leaf phenology”, on Thursday June 4th,  2020 at 12 noon EET in Finland (11 a.m. CET in the rest of continental Europe).

The defence is open to the public so you can watch the defence remotely with this link:

Or join the defence remotely with the following link:

And ask questions with this link:

Or in person, subject to some social distancing restrictions at: Porthania, Room P673.

Craig’s Opponent will be Professor Gareth K Phoenix from the University of Sheffield. Gareth is an ecophysiologist and expert on the response of plants and vegetation to climate change at high latitudes.  He will give a seminar on Wednesday 3rd June 2020 at 14:00, entitled:  Arctic Browning: extreme events causing large scale damage to arctic vegetation.
You can participate in the seminar of 3rd June using the following link:

Treharne et al., (2019) Arctic browning: Impacts of extreme climatic events on heathland ecosystem CO2 fluxes. Global Change Biology,

Surviving on the Edge

We are grateful to a grant  from HiLIFE Grand Challenges, Biological Resilience Seed Funding, allowing us to start work on the project: Surviving on the edge – trait syndromes that facilitate northerly species-range expansion.

This project will allow us to utilise a unique field-trial of Fagus sylvatica (European beech) at the University of Helsinki – far beyond the north-eastern limit of its range. Using such trials, we can compare the traits of populations in  new potentially stressful environments, giving us the tools to forecast how they will respond to climate change and potentially exploit more northerly regions of Europe.

In addition to field data, the project will test how trait information can be inserted into species distribution models. We will bring together experts in the field from Helsinki and beyond, to discuss how best to develop such models to provide informed forecasts of future species distributions. Armed with this knowledge, we will consider how policy makers, foresters, and conservation bodies might utilise this information in their work.

Newly thinned Helsinki beech-provenance trial in May 2020; with four populations covering the European range limits.

How does tree phenology respond to a warmer climate?

In the latest paper published in Agricultural and Forest Meteorology together with our collaborators from Bordeaux we consider the effect of warming on the phenology of European beech.

September, October, November relationships with Leaf senescence
The interactive relationship between leaf senescence and the mean temperature in September, October and November (Tm SON) for (a) the trial and (b) for the provenance.

Using ΔTrait Species Distribution Modelling of a large dataset from provenance trials, we established that not only earlier spring phenology but also delayed leaf senescence in northern populations allowed them to exploit warmer summer temperatures.

Beech is one of those forest trees that utilises a combination of temperature and day-length cues to prompt advancement of its annual growth cycle, meaning the climate warming and associated northerly range shifts have potentially complex outcomes for its phenology.

You can read the full paper open-access for 50 days: Greater capacity to exploit warming temperatures in northern populations of European beech is partly driven by delayed leaf senescence

Homero Gárate-Escamilla, Craig C. Brelsford, Arndt Hampe, T. Matthew Robson, Marta Benito Garzón, (2020) Greater capacity to exploit warming temperatures in northern populations of European beech is partly driven by delayed leaf senescence, Agricultural and Forest Meteorology, Volume 284,

Doctoral Course in Plant Responses to Climate Change

During the 3rd week of October at the University of Helsinki we ran an international course which considered how plant responses to light are mediated by environmental factors and the implications of climate change for plants’ capacity to adjust to their light environment.  The course, organised on behalf of the Doctoral Programme in Plant Sciences (DPPS), was attended by 13 visiting teachers and PhD students from all around Europe, in addition to the local participants from the University of Helsinki.

With the objective of understanding how plants scale their responses across levels of organisation, and respond to light over the appropriate time-scale for their environment, there were plenty of opportunities for students and teachers to develop inter-disciplinary knowledge and collaborations during the course.

We started the week considering photoreceptors and cell-cell signalling, and gradually scaled-up to look at the photosystem and chloroplast responses, physiological and biochemical mechanisms of photoprotection, the use of light in the timing of growth and flowering, and finally, plant traits, ecological and ecosystem levels.  A breadth of expertise was provided by an outstanding team of research leaders both from Helsinki and around Europe, giving really engaging lectures and stimulating discussions among the group.

International teachers and students enjoying the forest at Lammi Biological Station

The international participants rounded off the week with a visit to Lammi Biological Station to experience the Finnish forest, lake and hospitality!


UNEP EEAP panel preparing 2020 update

UNEP have put together a video explaining the work of the UNEP panels that assess ozone depletion, UV-B radiation and their interaction with climate change.

The UNEP Environmental Effects Assessment Panel in New Zealand

In late September, the UNEP Environmental Effects Assessment Panel met in Alexandra, New Zealand, home of Richard McKenzie, for our annual assessment of new research into the environmental effects of ozone depletion, UV radiation, and their implications with respect to climate change.

This year Janet Bornman, Paul Barnes, Carlos Ballaré, Sharon Robinson and myself were particularly tasked with understanding how plant-level effects on biodiversity and key ecological processes scale-up to the ecosystem level.  We also focussed on crosscutting themes affecting not only terrestrial ecosystems, but mankind and the entire global environment.

A traditional Pōwhiri – Māori welcome – for the UNEP panel.

The capacity for us to address ozone depletion through the successful implementation of the Montreal Protocol, which limited the production of ozone depleting chemicals, can be seen as a flagship example of our capacity to address global environmental problems through concerted international action.  In this respect, one of the panel’s responsibilities in future reports will be to provide quantitative comparisons of how our environment differs today from what it would have looked like without the Montreal Protocol.

The World Avoided – Projection of the UV index in March 2065 with (left) and without (right) the implementation of the Montreal Protocol – from Barnes et al., (2019) Nature Sustainability 2, 569–579

Do UV-radiation and blue light have a role in photodegradation affecting decomposition in Finnish forests over winter

The rate of decomposition of leaf litter on the forest floor controls the thickness of the litter layer and nutrient recycling within the ecosystem. Decomposition is well known to depend on moisture and temperature which hasten both the microbial and non-microbial breakdown of leaves following their autumn senescence.

In this paper, just accepted in Plant Physiology and Biochemistry we test the extent to which light plays a role in the decomposition of autumn leaves. Photodegradation, the process by which sunlight accelerates decomposition, has typically been considered important only in dry environments. However, Santa Neimane and Marta Pieristè found in this experiment that it can also participate in decomposition during winter and spring prior to forest canopy closure.

The paper also considers how photodegradation acts on leaves of silver birch and European beech. Using spectrally selective filters over leaf litter in the understorey of different stands in Viikki arboretum and under controlled conditions, the distinct roles of UV radiation and of blue light, which facilitates microbial colonisation could be identified.

The experiment also exploited natural UV filters found in the epidermis of leaves as a means to see whether screening UV-radiation from the mesophyll when leaves are orientated with their upper-face upwards would affect the rate of photodegradation.

This research formed part of Santa Neimane’s undergraduate thesis on Erasmus exchange in Helsinki. It complements the subsequent long-term study of decomposition in a temperate beech forest published this summer, Pieristè et al. 2019, which considers the dynamics of photodegradation in leaves of tree species spanning a continuum of succession.

Read more in the papers:

Pieristè M, Neimane S, Nybakken L, Solanki T, Jones AG, S, Forey E, Chauvat M, Ņečajeva J, Robson TM. (2020) Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of leaf litter from forest stands in southern Finland. Accepted in Plant Physiology and Biochemistry. PLAPHY5920.

Pieristè M, Chauvat M, Kotilainen TK, Jones AG, Aubert M, Robson TM, Forey E. (2019) Solar UV-A radiation and blue light enhance tree leaf litter decomposition in a temperate forest by accelerating photodegradation rate. Oecologia, 191(1), 191-203.

Understanding plants’ readiness to grow beneath the snowpack

A quick start to the growing season for plants emerging from the snowpack can provide them with a fitness dividend in locations where the summer is short.

In our latest paper, Transmission of ultraviolet, visible and near-infrared solar radiation to plants within a seasonal snow pack, just out in a Special Issue of PPS devoted to plant UV responses, we measured how much sunlight plants receive under snow and how the properties of the snowpack affect the irradiance spectrum.

Changes in the spectral composition of light under the snowpack may help plants perceive the onset of spring and physiologically prepare for exposure to the full sunlight and cold temperatures they will experience once they emerge.

This field work involved spending some very cold clear days hiding in deep snowpacks! 

Long-Term Ecological Research into plant UV adaptation high in the French Alps

Santa Neimane and Twinkle Solanki recording diurnal patterns in leaf optical properties of alpine plants under UV filters

We spent the last two weeks of May 2019 at the Station Alpin du Lautaret in the French Alps, which has been designated a Research Platform for long-term ecological studies under the framework of Horizon 2020 Transnational Access – who funded our research visit through the French National Centre for Scientific Research, CNRS.


Pedro J Aphalo measures solar radiation; to better understand how reflection from the snow pack affects exposure of plants in the environment.



Our team of researchers, collaborating with José Ignacio García Plazaola and Beatriz Fernandez-Marin from the University of the Basque-Country, to study how plants response to the steep increases in UV radiation that they receive on emergence from under snow cover in spring.

By characterising the patterns of response to UV radiation in terms of the photoprotection and UV-screening of plants across a diversity of species, we hope to better understand how and why these response evolved and what environmental cues underpin their induction.