Photosynthetic performance (CO2-compensation point, carboxylation efficiency, and net photosynthesis) of timothy grass (Phleum pratense L.) is affected by elevated carbon dioxide in post-volcanic mofette areas

Photosynthesis and growth of timothy grass (Phleum pratense) exposed to a naturally elevated CO2 regime in a post-volcanic mofette (cold CO2 emitting gas vents) area were drastically influenced. Plants carefully selected according to the soil CO2 within the rooting horizon showed a strong correlation between emitted CO2 and total plant height. Net photosynthesis measured at 2000 ppm CO2 (A2000) and even more net photosynthesis measured at 350 and 700 ppm CO2 (A350 and A700) were higher in “low-CO2-grown” plants (0.4% CO2 in the soil) than in plants that were exposed to medium (3.3%) or high (26%) soil CO2 levels during germination and growth. Carboxylation efficiency (CE) and the compensation point (CP) also drastically differed, with CE being much lower in high-CO2-grown plants (0.0023 μmol m−2 s−1 as compared to 0.0042 μmol m−2 s−1) and the compensation point being considerably higher (36, 93, and 144 μmol mol−1) within an increasing CO2 environment.