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European Beech Growth in Response to Rising CO2 and UV-B Radiation

Paper Reviewed
Uchytilová, T., Krejza, J., Veselá, B., Holub, P., Urban, O., Horácek, P. and Klem, K. 2019. Ultraviolet radiation modulates C:N stoichiometry and biomass allocation in Fagus sylvatica saplings cultivated under elevated CO2 concentration. Plant Physiology and Biochemistry 134: 103-112.

In providing the rationale for their work, Uchytilová et al. (2019) say that ultraviolet (UV) radiation induces a variety of responses in plants, including "DNA modifications and photorepair, formation of reactive oxygen species, accumulation of photoprotective compounds and antioxidants, and morphological changes." And with some scientists predicting that Earth's stratospheric ozone layer may experience further depletion in the future, there is concern that UV radiation will increase, potentially causing damage to terrestrial plant species. However, such damage could well be offset by accompanying growth enhancements due to atmospheric CO2 enrichment. Thus, it was the objective of this team of seven Czech scientists to investigate these potential outcomes.

To do so, Uchytilová et al. grew 3-year old European beech (Fagus sylvatica) saplings at a research site in the Beskydy Mountains of the Czech Republic under two atmospheric CO2 concentrations and one of three UV radiation treatments (UV-, UVamb and UV+, corresponding to UV-B doses of approximately 0, 10 and 16 kJ m-2 day-1, respectively) over a two-year period. CO2 concentrations were set at either 400 ppm (ambient) or 700 ppm (elevated), with the enriched treatment only being supplied during the growing season.

So what did their experiment reveal?

Surprisingly, UV radiation had little to no impact on plant biomass. Elevated CO2, on the other hand, had a positive impact on the growth of the European beech seedlings. As shown in the figure below, it stimulated aboveground biomass in the UV-, UVamb and UV+ treatments by 27%, 73% and 37%, respectively and by 46%, 56% and 21% for belowground biomass. Uchytilová et al. also report that saplings in the elevated CO2 treatment "were also taller and had greater basal stem diameter." Furthermore, they note that there was no statistically significant interactive effects between CO2 and UV radiation treatments, although the positive impact of CO2 on biomass at the highest UV treatment level was diminished from that observed at ambient UV levels.

In light of the above, it would appear that European beech trees will experience little, if any, biomass reductions in the future if UV radiation levels increase. But, if the air's CO2 content continues to rise, which it most likely will, great growth benefits will ensue via its aerial fertilization effect, resulting in a large stimulation of plant biomass both above and below ground.

Figure 1. Total aboveground biomass (left panel) and total root biomass (right panel) of European beech seedlings grown for two years at ambient (400 ppm) or elevated (700 ppm) CO2 under one of three UV radiation treatments (UV-, UVamb and UV+, corresponding to UV-B doses of approximately 0, 10 and 16 kJ m-2 day-1, respectively). The percentages in red text above each elevated CO2 column represent the percent change in biomass due to CO2 at that given UV-B radiation treatment. Source: Uchytilová et al. (2019).

Posted 17 June 2019