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 CO 2 spring in Iceland were used to investigate the long‐term (> 100 years) effects of elevated [CO 2 ] on photosynthesis, biochemistry, growth and phenology in a northern grassland ecosystem. Comparisons were made between plants growing in an atmosphere naturally enriched with CO 2 (≈ 790 μ mol mol –1 ) near the CO 2 spring and plants of the same species growing in adjacent areas exposed to ambient CO 2 concentrations (≈360 μ mol 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 [CO 2 ] on grassland ecosystems in Iceland are likely to be reduced by strong down‐regulation in the photosynthetic apparatus of the abundant N. stricta species.