Physiological reactions of grasses growing within natural CO2 springs and their probable use in remote sensing

Kurzfassung

If geogenous CO2 escaping from dry mofettes influences the temperature regime within and in the close vicinity of the vents, plants growing around the vents should be influenced. A probable temperature effect could result in (1) different stomatal behaviour which could affect transpiration, in (2) different photosynthetic efficieny and growth or (3) in pigment content and composition. Yet, plants growing in mofette fields are additionally affected by the direct effect of the elevated CO2 on above- and below-ground plant parts. Acidification of organelles as well as probable hypoxia will be deleterious for a normal functioning of the plant`s metabolism. Three different grass species ( Phleum pratense, Juncus effusus, and Echinochloa crus-galli) grown under a naturally elevated CO2 regime in a mofette area in N-Slovenia were examined and the physiological behaviour studied. In all cases the grasses showed a clear correlation between the prevailing CO2 regime and total plant height. Net photosynthesis measured at 2000 ppm (A2000) and even more net photosynthesis measured at 350 ppm and 700 ppm CO2 (A350 and A700) were higher in “low-CO2-grown” plants (0.4% CO2 in the soil) than in plants that exhibited medium (3.3%) or high (26%) soil CO2 during germination and growth. Theoretical maximum photosynthetic rates were obtained only when CO2 concentrations between 20.000 and 30.000 ppm. Carboxylation efficiency and the compensation point also drastically differed, with CE being much lower in high-CO2-grown plants. The compensation point (CP) proved to be much higher in plants growing in an increased CO2 environment. Also the pigment content and composition was changed within the given CO2 gradients. The use of these specific physiological parameters for the application in remote sensing studies of CO2-degassing vents will be discussed