Impacts Of Enhanced Ultraviolet-B Radiation On Mosses In A Subarctic Heath Ecosystem

Ecology, Sept, 1999 by Carola Gehrke

CONCLUSIONS

One of the main protective reactions against UV-B irradiation in vascular plants is the UV-B induced increase in the concentration of screening pigments, which was also shown in the bryophytes Bryum argenteum (Markham et al. 1990) and Sphagnum papillosum (Lindeberg 1996). In the current study, it is shown for the first time that the variability of the UV-B screening pigment concentration in plants can increase under enhanced UV-B radiation, although the mean concentration is unaffected.

It must be questioned whether bryophyte species are particularly sensitive to enhanced UV-B radiation initially, or on a time scale comprising a few years, compared to vascular plant species. In a subarctic heath ecosystem (50 m away from the heath in the present study), dwarf shrubs had been exposed to enhanced UV-B radiation for 2 yr (Johanson et al. 1995). Two of four dwarf shrub species showed reductions in length increment as early and in the same order of magnitude as H. splendens, although they are morphologically and functionally more complex than the bryophyte. Length increment in the other two dwarf shrub species remained unchanged over two years likewise to the functionally and morphologically analogous bryophyte P. commune. One may generally assume that the morphological and functional complexity of a species may enhance the ability of individuals to cope with disturbances initially or on a short-term scale. However, this does not seem to apply when the UV-B environment changes in a subarctic heath ecosystem.

This study and an investigation on a Sphagnum fuscum-dominated subarctic bog (Gehrke 1998) are the only UV-B studies at an ecosystem-level reported on, so far, which have involved bryophytes. In all three studied species, shoot growth and architecture were affected by enhanced UV-B radiation. Future enhancement of UV-B radiation may, besides affecting bryophyte growth and morphology, influence the variety of ecological roles bryophytes can play in ecosystems. Thus, this life-form needs to be considered when estimating impacts of enhanced UV-B radiation at an ecosystem level.

ACKNOWLEDGMENTS

This work was carried out within the UVECOS project financed by the European Commission under contracts No. EV5V-CT910032 and ENV4-CT96-0208. B. Wallen, L. O. Bjorn, B. A. Carlsson, and T V. Callaghan made valuable comments on this manuscript. A. Kiehl, K. Kilian, and J. Lindeberg helped during fieldwork. The director M. Sonesson and his staff at the Abisko Scientific Research Station provided logistical support. All are gratefully acknowledged.

LITERATURE CITED

Barnes, P. W., S. D. Flint, and M. M. Caldwell. 1995. Early-season effects of supplemented solar UV-B radiation on seedling emergence, canopy structure, simulated stand photosynthesis and competition for light. Global Change Biology 1:43-53.

Barsig, M., C. Gehrke, and K. Schneider. 1998. Effects of UV-B radiation on fine structure, carbohydrates and pigments in Polytrichum commune. The Bryologist 101:357-365.