UV Radiation and Subarctic Ecosystems
Subproject: Seasonal Variation in Photoprotective Pigments of Scots pine
Leader: Dr Minna Turunen Start of the project: 2001
Research group: Global Change End of the project: 2005
Research and central results
Arctic ozone levels have been significantly depleted in the past decade, particularly during the late winter and early spring. Current climate models suggest that stratospheric temperatures are likely to decrease in the coming decades as a result of increasing atmospheric concentrations of greenhouse gases. Below critical threshold stratosphere temperature, accelerated ozone depletion could consequently increase ultraviolet-B (UVB, 280-315 nm) radiation in northern regions. Model results anticipate a maximum 14 % increase in the annual UV dose in subarctic regions during the years 2010-2020 relative to those in 1972-1992. In the subarctic and Arctic ecosystems, the UV dose received by coniferous trees in the late winter and early spring is high due to the reflectance from long-lasting snow cover. Increasing UVB radiation, as a part of global climate change, represents a potential risk for plant growth, physiology and quality (Figure 1).
The main aim of this study was to explore the effect of manipulated UV-radiation on both UV-screening and photosynthetic pigments in Scots pine (Pinus sylvestris L.) needles in northern latitudes, particularly during stressful spring conditions. Both phenolics (including flavonoids) and photosynthetic pigments (including xanthophylls) are important in photoprotection of the plant photosynthesis machinery.The effects of UV-radiation on the photosynthetic and UV-screening pigments in needles of Scots pine saplings were studied in a UV-exclusion field chamber experiment in northern Finland (67°N) during 2001-2002. The chambers held filters that excluded both UVB and UVA, only UVB, transmitted all UV, or lacked filters (Kallo et al. 2003, Turunen et al. 2004, 2005) (Figure 2).
Figure 1. Early spring conditions can be stressful for evergreen foliage of Scots pine due to the reflectance of UV radiation from long-lasting snow cover. Photo: Minna Turunen
Figure 2. UV exclusion field chambers in Sodankylä,
Finland. Photo: Minna Turunen
Exclusion of UV radiation significantly affected the xanthophyll cycle but not the other photosynthetic pigments analysed. Under UVA/B exclusion, the epoxidation state of xanthophyll cycle pigments (EPS) was increased and violaxanthin-antheraxanthin-zeaxanthin (VAZ) pool size was unchanged in April, whereas EPS remained unchanged and the VAZ pool size was reduced in May and June. A HPLC analysis of soluble phenolics showed that the exclusion of UVA/B radiation caused a significant effect on five compounds out of 46 studied, without affecting the concentration of the total soluble phenolics. Under UVA/B exclusion, the concentration of three of them (secoisolariciresinol-glucopyranoside, two unknown) was reduced while the concentration of dicoumaroyl-astragalin and pinosylvin monomethylester was increased compared to both controls separately. In general, the exclusion of UVA/B caused a stronger effect than the exclusion of UVB on both photosynthetic and UV screening pigments. The effects of UV radiation on xanthophyll cycle pigments were season-specific and detectable only under stressful spring conditions (freezing temperatures and high irradiance due to snow reflection). The effect on the xanthophyll cycle could be a direct consequence of UV treatments, or an indirect consequence of the changed flavonoid composition, or a combination of both (Martz et al. 2007).
In Scots pine needles, exclusion of UV radiation induced a compound-specific modification of the secondary metabolism and a time-specific modulation of the dynamic and sensitive systems of photoprotection. Significant modulation of the xanthophyll cycle by UV-radiation in stressful spring conditions is in agreement with the idea that UV effects on plants are hardly detectable under ideal growing conditions, but significant effect can be observed in combination with other abiotic or biotic stresses. UVB is efficiently screened through the epidermal layers but changes in the low UVB dose reaching the mesophyll cells are here enough to induce a response at the level of the photosynthesis machinery in the Scots pine needles. This result highlights the sensitivity of the photoprotection system but it also raises the question of the origin of the UV effect on the xanthophyll cycle pigments. The effect on the xanthophyll cycle could be a direct consequence of UV exclusion, or an indirect consequence of the changed phenolic composition, or a combination of both. In the case of an indirect effect, it would suggest that a few, one, or a combination of these five phenolics is important in the regulation of the xanthophyll cycle (Martz et al. 2007).
Martz, F., Sutinen, M.-L., Derome, K., Wingsle, G., Julkunen-Tiitto, R., TURUNEN, M. (2007) Effect of UV-exclusion on the seasonal content of photosynthetic and UV screening pigments of Scots pine needles. Global Change Biology 13:252-265. Download full text [pdf].
TURUNEN, M., Latola, K. (2005) UV-B radiation and acclimation in timberline plants. Environmental Pollution 137, 390-403. Download full text [pdf].
TURUNEN, M., Sutinen, M.-L., Derome, K., Krywult, M., Smykla, J., King, S., Lakkala, K. (2005) Ecophysiological responses of subarctic Scots pines to ultraviolet (UV) radiation. Polish Botanical Studies 19, 143-150. Download full text [pdf].
TURUNEN, M., Martz, F., Sutinen, M.-L., Derome, K., Huttunen, S., Wingsle, G., Julkunen.-Tiitto, R., Lakkala, K. 2004. UV radiation and photoprotective pigments in Scots pine saplings (Pinus sylvestris L.). Poster Session A2: Paper 16 (4 pages). The ACIA International Scientific Symposium on Climate Change in the Arctic. Reykjavik, Iceland, 9 – 12 November, 2004. Extended abstracts. Arctic Climate Impact Assessment (ACIA) AMAP Report 2004:4.
TURUNEN, M., Latola, K. 2004. UV-B radiation and timberline plants. Poster Session A2: Paper 17 (4 pages). Extended abstracts. ACIA International Scientific Symposium on Climate Change in the Arctic. Reykjavik, Iceland, 9 – 12 November, 2004. Extended abstracts. Arctic Climate Impact Assessment (ACIA) AMAP Report 2004:4.
Kallo, K., Derome, K., TURUNEN, M., Sutinen, M.-L., Julkunen-Tiitto, R. 2003. Development of a method for analysing soluble phenolics by HPLC in Scots pine needles from the subarctic. Pp. 256-259. In: Proceedings of the Sixth Finnish Conference of Environmental Sciences, Joensuu, Finland, May 8-9, 2003. Finnish Society for Environmental Sciences. University of Joensuu.
• Professor Marja-Liisa Sutinen, Finnish Forest Research Institute, Finland
• Dr Francoise Martz, Finnish Forest Research Institute, Finland
• Kirsti Derome, Head of Laboratory, Finnish Forest Research Institute, Finland
• Professor Riitta Julkunen-Tiitto, University of Joensuu, Finland
• Professor Gunnar Wingsley, Umeå University, Sweden
• Dr Marek Krywult, Dr Jerzy Smykla, Polish Academy of Sciences, Poland
• Professor Satu Huttunen, University of Oulu, Finland
Dr Minna Turunen
Arctic Centre, University of Lapland