Both climate change and it potential solutions involving climate manipulations cause shifts in direct and diffuse sunlight that plant canopies receive (e.g. under clouds or aerosols). Photosynthesis at the whole-canopy scale is more efficient under diffuse than direct light; as diffuse radiation penetrates further into the canopy. But we lack knowledge of how canopies adjust to receiving diffuse radiation and the mechanisms as allow greater efficiency in light use.
Knowledge of canopy-level light use efficiency are of both ecological and practical value: these data provide input to models of global carbon assimilation and can be useful in crop improvement.
Large seasonal changes in sunlight and its spectral composition are challenging for greenhouse growers in commercial horticulture. This is particularly true for growers at high latitudes like Finland.
Better informing growers of the light environment within greenhouses throughout the year and how the of use of lamps with bespoke spectra, and output optimised for specific crop species, allows efficiency saving to be made.
At GreenSys 2019 in Anger, France 16-20 June 2019, Titta Kotilainen will present our research showing how greenhouse lighting subjects plants to different light spectra for photosynthesis depending on the time of year and location of greenhouses.
Titta Kotilainen will discuss how better selection and management of the light environment, through greenhouse materials, shade screens and insect nets, and appropriate lighting, improves crop yield and reduces energy costs.
Robson TM, Kotilainen TK. (2018) Transmittance of spectral irradiance by climate screens and nets used in horticulture and agriculture (Version 1.1.1) [Data set]. Zenodo. http://doi.org/10.5281/zenodo.1561317
Kotilainen TK, Robson TM, Hernández R. (2018) Light quality characterization under climate screens and shade nets for controlled-environment agriculture. PLoS ONE 13(6): e0199628. https://doi.org/10.1371/journal.pone.0199628
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.
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 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.
Is there potential to apply our knowledge that plant phenolic compounds respond to UV-B radiation to infer past changes in global solar UV-B irradiance? This is the possibility that we explore in a Perspective paper just out in Photobiological & Photochemical Sciences.
Our collaborators from the University of Bergen in Norway and University of Innsbruck intend to test the potential for us to use fossilised pollen grains to do just that. By testing whether the UV-screening phenolics in the pollen of trees growing today tracks their exposure to UV-B radiation they will try to establish a mechanistic link that will allow past UV irradiances to be revealed in cores of fossilised pollen.
In this perspective piece we formulate a model for how this approach might be put into practice.
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
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.
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 packPlant Physiology and Biochemistry. https://doi.org/10.1016/j.plaphy.2018.09.003