How can we compare solar spectra with each other?

Assessing differences in spectral irradiance is at the heart of our research group’s work, and yet considering entire spectra at once is not something that is straight-forward to do. Traditionally, most research has broken-down spectra into their component regions in order to compare one light environment with another, but looking at the whole spectrum has the potential to yield much more detailed information.

Our open-access paper just out in Ecology & Evolution considers ways to quantitatively assess differences between entire solar spectrum. This approach is illustrated by tracking changes in the forest canopy through the spring and amongst stands dominated by different tree species.

The method we used, called thick pen transform, involves redrawing our spectra of interest with increasingly thick lines and then comparing their similarity. This allows the coarse and fine features of spectra to be compared, and a “Thick Pen Measure of Association” to be calculated to quantify their similarity, as illustrated above.

Using this technique, we were able to trace differences in the spectral irradiance at ground level between forest stands of birch, oak, and spruce at Lammi Biological Station in central Finland. This is the first time such fine-scale differences in the light environment due to the species, phenology, height and leaf-optical properties of canopies have been distinguished. By better understanding how light environments in forests differ we can start to better explain the factors that control species composition and ecosystem functioning in these environments.

As well as detailing the theory and methodology behind this research, the paper gives a comprehensive protocol of how to maximise the information obtained from hemispherical photos of the forest canopy. These are used to assess leaf area index and the sunlight reaching the floor throughout the year.

Read the full text at Hartikainen SM, Jach A, Grané A, Robson TM. Assessing scale‐wise similarity of curves with a thick pen: As illustrated through comparisons of spectral irradiance. Ecol Evol. 2018;00:1–13.

Improving the use of sunlight in plant production environments

Last Tuesday I presented the results of our Key Funding Academy of Finland Project to enhance the practical application of our research at an event for policy makers and civil servants at Finlandia Hall, Helsinki.

Our project helps farmers and growers in the horticultural industry better manage the light that plants receive in greenhouses and polytunnels through selecting appropriate material for windows, nets and screens. It was one of just nine projects selected for poster-pitch presentation at this event which marks the culmination of this initiative. All nine are available to watch on the Academy of Finland’s website.


Springtime recovery of Vaccinium vitis-idaea leaves above and below the snow pack

In Arctic and alpine environments warming temperatures are expected to result in longer growing seasons and to encourage growth, but snow will melt faster and more will fall as rain. This means that the protective winter blanket of snow cover may no longer be present to hide plants from the extremes of cold that periodically occur. Whether plants can overcome this paradox to benefit from the increased sunlight and warmth above the snow, while resisting the greater fluctuations in temperature, will depend on their physiological capacity to cope with the changing conditions.

Is the paper, Solanki et al., 2018, published in a special issue of Plant Physiology and Biochemistry on UV-cross protection, we explore the ecophysiological response of Vaccinium hummocks to snow cover over the course of a year in central Finland.

Twinkle Solanki taking Dualex measurements in central Finland

We focus on the role played by UV-absorbing compounds in protection against high light and low temperature combinations as shoots emerge from under snow in the early spring.

Solanki T. et al., 2018 UV-screening and springtime recovery of photosynthetic capacity in leaves of Vaccinium vitis-idaea above and below the snow pack Plant Physiology and Biochemistry

Allocation to root growth can determine the survival of Mediterranean oaks during seasonal drought

The range of Holm oak (Quercus ilex), green; cork oak (Q. suber), purple; and their overlap, brown. Circle sample site, and triangle the field experiment.

Complex trade-offs in allocation to growth can determine the success of oak species where their ranges overlap.

This is highlighted by our paper Ramírez-Valiente et al., (2018), where higher root investment under seasonal drought by cork oak gave it an advantage over Holm oak, despite our prior expectations that the latter species is more drought tolerant.

Acorns germinating under controlled conditions prior to planting in the experimental plot

José-Alberto Ramírez-Valiente, Ismael Aranda, David Sanchéz-Gómez, Jesús Rodríguez-Calcerrada, Fernando Valladares, T Matthew Robson; Increased root investment can explain the higher survival of seedlings of ‘mesic’ Quercus suber than ‘xeric’ Quercus ilex in sandy soils during a summer drought, Tree Physiology, , tpy084,

Remotely monitoring seed fall in beech stands

Following on from the publication of our database on the network of European beech trials in Scientific Data earlier this month, I spent last week with Marta Benito-Garzon & Santa Neimane in one UK trial testing a new approach to monitoring beechnut production.

A seed trap installed in Little Wittenham trial, Oxfordshire. Seeds falling through the tube are automatically recorded and the information relayed back to a central computer

The prototypes will be deployed over this autumn and then optimized to register only falling seeds, not leaves or other objects, by validating the beechnut counts against the number of seeds caught in the bags beneath.

Once perfected the electronic monitoring system, designed by Marta Benito-Garzon (INRA Bordeaux) will allow researchers to follow the timing of autumn seed dispersal in real time from the comfort of their offices!

How does plant photoprotection respond UV-A radiation?

Short wavelengths within the UV-A region of the solar spectrum fall between the known action spectra of the UV-B photoreceptor, UVR8, and the photoreceptors CRYPTOCHROME and PHOTOTROPIN which are predominantly blue light and long-wave UV-A photoreceptors.  Our new paper, out in Physiologia Plantarum today questions the roles played by these photoreceptors in response to UV-A and whether radiation in the blue and UV-A regions can help prime plant photoprotection for subsequent high irradiance.

Craig Brelsford and Matt Robson take leaf chlorophyll fluorescence measurements under high irradiance.

Find the paper here: Brelsford et al., (2018) Do UV‐A radiation and blue light during growth prime leaves to cope with acute high light in photoreceptor mutants of Arabidopsis thaliana?

Quantifying the phenotypic and genotypic variation among European beech populations

Craig Brelsford of the University of Helsinki, (CanSEE group) scores spring phenology in the CostE52 European beech provenance trial in La Rioja Spain.

The culmination of more than 10 years of data collection and analysis, a database of beech traits from over half a million trees planted in a common-garden experiment covering the whole of Europe is out today in Scientific Data.

This resource should help researchers better assess the impacts of climate change on species ranges. The most comprehensive dataset of its kind, it promotes beech as a model species on which to test ideas about the relative importance of intra-specific plasticity and genetic variability in helping populations cope with a changing climate.

You can find the paper here: Robson T.M., Benito Garzon M., BeechCoste52 database consortium (2018) Phenotypic trait variation measured on European genetic trials of Fagus sylvatica L. SCIENTIFIC DATA | 5:180149 | DOI: 10.1038/sdata.2018.149

Here is a press release  from INRA in France, and other press releases from the resilience blog of the European Forestry Institute and its sister institute EFIMED.

Is photodegradation an important process in forest understoreys?

We’ve just returned from a 10-day field trip to Japan where our collaborators Qingwei Wang and Hiroko Kurakawa are studying the effects of shortwave solar radiation on the growth and subsequent decomposition of leaves from shade tolerant and light demanding plant species in controlled experiments under low and high light conditions.

Marta Pieriste takes hemispherical photos amongst litter sachets on the beech forest floor
Qingwei Wang checks his filter experiment testing understorey plant response to removal of UV-B, UV-A, blue and green sunligh

This visit included a fascinating trip to a beech forest in central Japan to an experiment where the rate of leaf litter decomposition is being compared over 1-year on the forest floor and in an open area under filters screening out various parts of the solar spectrum, in an attempt to estimate the role that photodegradation plays in the decomposition from leaves of different functional types of forest plant in open and shaded environments.



A complimentary experiment at the Forestry and Forest Products Research Institute in Tsukuba City is testing how these species grow under waveband-selective filters, and whether generalisations between plant life forms can be made about the role of these different wavebands in growth and physiology as well as decomposition.

Understanding contemporary UV effects on pollen to reconstruct UV exposure over geological time

We recently traveled to Austria to help set-up our collaborators’ experiments monitoring the effects of UV-B radiation exposure on Pinus cembra pollen in the mountains above Innsbruck.  If we can understand how exposure to UV radiation affects the accumulation of UV-absorbing compounds in pollen today, we may be able to calibrate the concentrations of these compounds found in ice- and sediment cores used in climatic reconstructions. This information potentially will allow palyontologists to understand how UV radiation changed over geological time and what the implications of these changes might have been for the Earth’s ecosystems. By better understanding past climate we will be better prepared to forecast how modern-day changes in UV radiation might affect the Earth’s ecosystems.

Here we take parallel measurements with broadband UV-B sensors and a spectroradiometer next to a specimen pine tree during the period before flowering.

Find up more in last years UNEP update.

Effect of horticultural shade screens and nets on spectral quality

Shade screen and net are used to control the environment of plants growing in polytunnels and greenhouses but they have some unintended consequences in modifying the spectrum of light that plants receive.

Titta Kotilainen has a new article out describing these effects and what they imply for the use and selection of these products. Check it out in PLOS one – HERE!

We recently spent the week at GreenTech Expo in Amsterdam finding out more about innovations in LED lighting and spectral manipulation of the light used in plant production scenarios. In response we are preparing an extended a continuation of our research into spectral quality with an extended dataset of screen and net assessments.