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. https://doi.org/10.1016/J.PLAPHY.2019.11.005
  • 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. https://doi.org/10.1007/s00442-019-04478-x
  • Pieristè et al., (2020) Sunlight affects the microbial functional structure of beech leaf litter. Plant & Soil, https://doi.org/10.1007/s11104-020-04557-6
  • 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: http://video.helsinki.fi/unitube/live-stream.html?room=l22

Or join the defence remotely with the following link: https://helsinki.zoom.us/j/65397468863?pwd=cjEwdk5rRzdvUGxYaXloRTB2bmJaZz09

And ask questions with this link: https://presemo.helsinki.fi/p673

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: https://helsinki.zoom.us/j/63529246088?pwd=V3NTeFp0SjE4VzZnSlB4VVR0N1NBZz09

Treharne et al., (2019) Arctic browning: Impacts of extreme climatic events on heathland ecosystem CO2 fluxes. Global Change Biology, https://doi.org/10.1111/gcb.14500

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,
107908, https://doi.org/10.1016/j.agrformet.2020.107908.

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 https://www.nature.com/articles/s41893-019-0314-2

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. https://doi.org/10.1016/j.plaphy.2019.11.005

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. https://doi.org/10.1007/s00442-019-04478-x

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! 

Range‐wide variation in local adaptation and phenotypic plasticity of fitness‐related traits

Last year, we published a database of traits from European beech provenance trials; the most extensive set of such data to be collected (Robson, Benito-Garzon et al, 2018 Scientific Data), and earlier this year provided a road map of how to use these sort of trait data in Species Distribution Model to predict responses to climate change (Benito-Garzon et al., 2019 New Phytologist). So it’s fitting that Homero Garate, working with Marta Benito-Garzon in Bordeaux in collaboration with us, should give a practical illustration of the application of these models to this data set, presented here in a new paper just out in Global Ecology and Biogeography.

Spatial projections of vertical growth (cm) for (a) vertical‐radial growth model and (b) vertical growth‐leaf flushing models

The paper entitled, Range‐wide variation in local adaptation and phenotypic plasticity of fitness‐related traits in Fagus sylvatica and their implications under climate change, quantifies local adaptation and phenotypic plasticity of vertical and radial growth, leaf flushing and survival across the species range to estimate the contribution of each trait towards explaining occurrence.

 

The place of spectral composition among cues controlling tree phenology

In this review, just out in Tree Physiology, we assess the literature researching how the composition of UV, blue, and red/far-red regions of the spectrum affect bud burst and leaf senescence  phenology.

The role of plant photoreceptors in detecting diurnal shifts in spectral composition

The effect of climate change on phenology is a strong determinant of fitness. But shifts in the timing of annual events and the polewards displacement of species ranges both have the potential to interfere with the interactive control of phenology by temperature and photoreceptor-mediate processes.  This dictates that to anticipate plant responses to climate changes, we must gain an understanding the mechanisms underlying the role of spectral composition in phenology.

These ideas and more are explored in the Tree Physiology review article, Brelsford et al., 2019: The influence of spectral composition on spring and autumn phenology in trees. https://doi.org/10.1093/treephys/tpz026

Moving Forward in Plant-UV Research

Our new and comprehensive review and perspective on the future of plant-UV research assimilates the knowledge and insight across the breadth of plant science from researchers in UV4Plants Association. We hope that it will inspire researchers in their attempts to better understand plant responses to UV radiation and to put this knowledge to practical use.

Let us know what you think! Photochemical & Photobiological Sciences, 2019, DOI: 10.1039/C8PP00526E