Methane emissions from trees driven by solar radiation & temperature

Tree planting is seen as a mitigation strategy to remove greenhouse gas from the atmosphere, as trees fix carbon dioxide by photosynthesis, but trees also emit various organic compounds that act as greenhouses gases, and it is important to quantify these emissions to understand the scales of the net benefit of trees and forests against greenhouse warming.

In 2009, Brüggemann et al., reported that plant shoots receiving UV radiation under controlled laboratory conditions may emit significant amounts of methane, a powerful greenhouse gas. This finding triggered a cascade of research which eventually established that although methane is produced abiotically by plants under controlled conditions the amounts of methane they produce in natural sunlight conditions is several orders of magnitude less than what was originally thought (Bloom et al., 2010; McLeod et al. 2008).

This new study, led by Salla Tenhovirta and Lukas Kohl, concluded an ambitious project to scale the emissions of methane by trees across lab, greenhouse, common garden, and ecosystem studies. The research also established whether these emissions in the boreal forest as largely biotic or abiotic, and whether temperature, sunlight or other factors are their main drivers.

Researchers from Matt Robson’s CanSEE group guided the design and interpretation of the UV radiation element of this work, a small but important part of the much wider project directed by Mari Pihlatie’s research group.


Bloom et al., Global methane emission estimates from ultraviolet irradiation of terrestrial plant foliage. New Phytol. 187, 417–425 (2010).

Brüggemann et al., Nonmicrobial aerobic methane emission from poplar shoot cultures under low-light conditions. New Phytol. 182, 912–918 (2009).

McLeod et al., Ultraviolet radiation drives methane emissions from terrestrial plant pectins. New Phytol. 180, 124–132 (2008).

Tenhovirta et al., Solar radiation drives methane emissions from the shoots of Scots pine. New Phytol. 235, 66–77 (2022).

Kohl, Tenhovirta et al., Radiation and temperature drive diurnal variation of aerobic methane emissions from Scots pine canopy. PNAS. 120 (52) e2308516120, (2023).

Extended canopy closure under with mild autumns, and its effect on the understorey growing season

In a new paper just out in Agricultural and Forest Meteorology, we explore how extended canopy closure in oak and birch forests at Lammi Biological Station in southern Finland affects the growing season for common understorey forbs.

Undergraduate student Arthur Daviaud sampling the understorey at Lammi Biological Station for the project which lead to this paper. Arthur was supervised by Maxime Durand (University of Helsinki) and Matthew Robson (University of Cumbria) from CanSEE group.

The paper describes an experiment to test the effects of climate warming which may extend the length of time that canopy trees in a forest keep their leaves into the winter. One puzzle associated with climate change is whether plants growing on the forest floor benefit more from the extended warm periods in the spring and autumn, or whether these warm periods mean that canopy trees retain their leaves for longer and thus restrict the light reaching the ground and available there for photosynthesis.

Autumn colouration of iconic understorey forb Hepatica nobilis
Autumn colouration of iconic understorey forb Hepatica nobilis

In an experiment comparing stands of oak, birch and spruce, we tested the potential for photosynthesis, retention of chlorophyll, and colouration of understorey plant species on the forest floor throughout autumn and the start of winter. Our main finding was that the increase in light received and change in its spectral composition following canopy leaf fall was the main trigger of senescence in the understorey. Those understorey species able to keep photosynthesizing effectively into late autumn were benefitting the most from warmer temperature and an extended closed canopy period.

Spruce scene in summer and winter
Seasonal changes in the boreal spruce forest

Functional role of aquaporins models plant to beech trees: David Israel’s PhD defence

The public PhD defence of David Israel is on Friday 27th Jan 2023 13:15-15:15 EET with opponent Oliver Brendel from INRAE at Nancy, France.

David Israel: The ecophysiology of plasma membrane aquaporins in Arabidopsis thaliana and Fagus sylvatica
Biokeskus 2, auditorio 1041, Viikinkaari 5

This research makes the connection from expression of aquaporins in plant membranes to identify their functional role in plant water use, growth and photosynthesis, under imposed stress and seasonal changes in the environment of both model plants and European beech trees.

David’s research is published in four papers:

Israel D, Lee SH, Robson* TM, Zwiazek* JJ (2022) Plasma membrane aquaporin PIP2;3 facilitates hydrogen peroxide transport into root cells, meaning Arabidopsis knockout mutants lacking this function grow more when under oxidative stress. BMC Plant Biology 22, 566.

Israel D, Durand M, Salmon Y, Zwiazek JE, Robson TM, (2023) Genome-wide identification of Fagus sylvatica aquaporins and their comparative spring and late-summer expression profiles.  Trees: Structure and Function 1-16,

Israel D, Khan S, Warren CR, Zwiazek J,* Robson TM* (2021) The contribution of PIP2-type aquaporins to photosynthesis in response to increased vapour pressure deficit. Journal of Experimental Botany 72(13) 5066–5078. erab187,

Wang F, Israel D, Ramírez-Valiente J-A, Sánchez-Gómez D, Aranda I, Aphalo PJ, Robson TM. (2021) Seedlings from marginal and core populations of European beech (Fagus sylvatica L.) respond differently to imposed drought and shade. Trees Structure and Function, 35, 53-67.

David Israel making gas exchange measurements.
David Israel making gas exchange measurements.

Sunflecks in the crops & forests

Fast fluctuations in light condition plant photosynthesis within canopies of crops and in forests. In a series of recent publications, we consider both the dynamics of these changes in illumination and what they mean for plant photosynthesis.

In crop canopies movements in the wind create extremely fast fluctuations defined as windflecks, while in forests the greater canopy depth means that differences in spectral composition between sunflecks and shade can be important for the ecophysiology of photosynthesis and its induction.

Our three recent publications below take the first steps towards describing the processes involved at the canopy level. They (1) defines sunflecks, (2) explain how they are modified by (5) a crop canopy and (4) a forest canopy. We also consider how (3) leaf morphology, (6) pigmentation and senescence change when we manipulate light quality under the canopy.

(1) Durand M, Matule B, Burgess A, Robson TM (2021) A method to identify and measure sunfleck properties from irradiance time series of fluctuating light in agricultural crop canopies. Ag. For Met. 308-309 108554

(2) Burgess AJ, Durand M, Gibbs JA, Retkute R, Robson TM*, Murchie EH*. (2021) The effect of canopy architecture on the patterning of ‘windflecks’ within a wheat canopy. Plant Cell and Environment, 4411), 3524– 3537

(3) Wang Q-W, Liu C, Robson TM, Hikosaka K, Kurokawa H (2021) Leaf density and chemical composition explain variation in leaf mass area with spectral composition among 11 widespread forbs in a common garden. Physiologia Plantarum. 173: 698–708

(4) Durand M, Stangl ZR, Salmon Y, Burgess AJ, Murchie EH, and RobsonTM. (2022) Sunflecks in the upper canopy: dynamics of light-use efficiency in sun and shade leaves of Fagus sylvatica. New Phytologist. 235:1365–1378. Major Revision 04/03/2022, Accepted 08/05/2022.

(5) Durand M, Robson TM (2023) Canopy architecture determines how wind affects sunflecks. Revised for New Phytologist, 08/01/2023.

(6) Brelsford CC, Trasser M, Paris T, Hartikainen SM, Robson TM. (2022) Understorey light quality influences leaf pigments and leaf phenology in different plant functional types. Physiologia Plantarum, 174( 3), e13723.

Monitoring understorey traits
Craig Brelsford of the University of Helsinki, CanSEE group scores spring phenology in the CostE52 European beech provenance trial in La Rioja Spain

Plant species adaptation to high irradiances in the French Alps

Among plant species there are large differences in photoprotection against high irradiance and UV radiation. To explore how these differences are driven by taxonomic relatedness, geographical origin, and local environment we compared a huge database of plant species growing in alpine and boreal botanical gardens.

Hartikainen SM, Robson TM (2022) The roles of species’ relatedness and climate of origin in determining optical leaf traits over large set of taxa from high elevation and latitude. Frontiers in Plant Science 13 .

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

The Station Alpin du Lautaret in the French Alps, is 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.


We collaborated 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.

Solanki T, García Plazaola JI, Robson TM*, Fernandez-Marin B* (2022) Comparative Assessment of Changes in Leaf Transmittance in Alpine Plant Species Following Freezing. Photochemical & Photobiological Sciences.

Fernández-Marín B, Sáenz A, Solanki T, Robson TM, García-Plazaola JI, (2021) Alpine forbs rely on different photoprotective strategies during spring snow melt. Physiologia Plantarum. 172, 1506-1517.

Photodegradation contributes to forest leaf litter decomposition

Qing-Wei Wang and Marta Pieriste inspecting leaf-litter decomposition filters in the understorey site of a Japanese beech forest

The spectral composition of light in a forest gap and understorey through the year affects the rate of photodegradation of senescent leaf litter material across a variety of native plant species. This finding that photodegradation plays an important role in forest litter decomposition  could partially explain the hole in the carbon budget in this ecosystem.

Wang QW, Pieristè M, Kenta T, Liu C, Robson TM, Kurokawa H (2020) Photodegradation enhances litter decomposition modulated with canopy openness in a temperate forest. New Phytologist. NPH17022

Enhanced decomposition can occur through direct photochemical mineralisation, but in temperate forests effects of increased temperature and the availability of substrates for microbial decompositions can be even more important. These research supports findings of our meta-analysis, that actions of photofacilitation are highly wavelength dependent and the subtilties of these responses can only be identified through very large scale experimental manipulations of sunlight, as was done in this ambitious experiment.

Wang Q-W, Robson TM, Pieristè M, Kenta T, Kurokawa H. (2022) Photodegradation dynamics below a forest canopy. Science of the Total Environment 820 153185.

Wang Q-W*, Pieristè M*, Kotilainen TK, Forey E, Chauvat M, Kurokawa H, Robson TM, Jones AG. (2022) The crucial role of blue light as a driver of litter photodegradation in terrestrial ecosystems.  Plant & Soil,

Defining the success of the Montreal Protocol as a global climate treaty

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With COP26 so prominently in the headlines it is prescient to consider the effects of the Montreal Protocol limiting ozone depleting chemicals as both a success in halting the increase in UV radiation & as a global effort to reduce greenhouse gas emissions.

This success story is explained in our recent piece: Barnes et al., (2021).  Global Change Biology275681– 5683

The recent Nature paper Young et al., 2021 considering the “World Avoided” by the Montreal Protocol was further explored by Simon Clark below.