Effects of long-term elevated [CO₂] from natural CO₂ springs on Nardus stricta: Photosynthesis, biochemistry, growth and phenology

Plants of Nardus stricta growing near a cold, naturally emitting CO₂ spring in Iceland were used to investigate the long-term (> 100 years) effects of elevated [CO₂] on photosynthesis, biochemistry, growth and phenology in a northern grassland ecosystem. Comparisons were made between plants growing in an atmosphere naturally enriched with CO₂ (≃ 790 μmol mol^-1) near the CO₂ spring and plants of the same species growing in adjacent areas exposed to ambient CO₂ concentrations (≃ 360 μmol mol^-1). Nardus stricta growing near the spring exhibited earlier senescence and reductions in photosynthetic capacity (≃25%), Rubisco content (≃26%), Rubisco activity (≃40%), Rubisco activation state (≃23%), chlorophyll content (≃33%) and leaf area index (≃22%) compared with plants growing away from the spring. The potential positive effects of elevated [CO₂] on grassland ecosystems in Iceland are likely to be reduced by strong down-regulation in the photosynthetic apparatus of the abundant N. stricta species.