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

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. https://doi.org/10.1002/ece3.4496

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 Biochemistryhttps://doi.org/10.1016/j.plaphy.2018.09.003

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, https://doi.org/10.1093/treephys/tpy084

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? https://doi.org/10.1111/ppl.12749

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.

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.

Finnish Growers’ Association highlight our research into the greenhouse light environment

 

Some results from our Academy of Finland Key Funding project were recently presented by Titta Kotilainen in the Finnish Growers’ Association “Puutarha & Kauppa” magazine. Climate screens that are typically used inside greenhouses to manage humidity and temperature alter light transmission, resulting in large differences in both the fraction of irradiance attenuated and spectral ratios received underneath.

Different climate-control screens, that are superficially very similar in terms of their appearance and texture, have very different effects on the light environment, which would go unnoticed without this sort of measurement. Spectral characterization of this nature is required to interpret the results of studies examining plant responses to different greenhouse screens. Material manufacturers, growers, and horticultural consultants can all benefit from these data aiding the selection of material to better match the desired end-results.