Effects of H2S on CO2 gas exchanges and growth rates of the epiphytic lichen Parmelia sulcata Taylor

The results of a study on the effects of hydrogen sulphide on CO2 gas excha nges and radial growth of Parmelia sulcata are presented. Field work was ca rried out in a chestnut wood of Acquapassante (Mt. Amiata, Central Italy) n ear a vent emitting H2S and CO2. Gas exchanges were measured at optimal con ditions using crossed transplanted thalli collected and re-exposed at 16-30 m from the vent (zone A; maximum H2S concentration: c.2 ppm) and at more t han 130 m (zone C; maximum H2S concentration: c. 5 ppb). Corrections for te mperature were made using temperature-dependent curves obtained in the labo ratory. Radial growth rates were measured every three months in three popul ations occurring in A, C and in the intermediate zone B, 50-80 m from the v ent. The results show that the metabolism of P, sulcata is strongly affecte d by H2S. At low concentration inhibition of photosynthesis occurs, but the phenomenon is possibly reversible; a prolonged exposition seems to cause p ermanent damage to the photosynthetic apparatus, with a decrease in photosy nthetic capacity, causing a drastic decrease in thallus growth.