Long term effects of naturally elevated CO2, H2S and SO2 on sulphur allocation in Quercus

The thiol composition and contents were analysed in oak trees growing at sites with naturally elevated atmospheric CO2 and sulphur concentrations. Exposure to these gases leads to enhanced thiol contents in metabolically active tissues such as leaves and bark. In both tissues GSH was the predominant thiol. The additional reduced sulphur in leaves and bark seems to originate from atmospheric sulphur influx, since sulphur contents of the xylem sap remained unchanged. In contrast to xylem sap, GSH contents of phloem exudates decreased at elevated compared to ambient CO2 and sulphur independent of the site studied. Enhanced thiol contents in the bark, but reduced thiol contents in the phloem under elevated CO2 and sulphur indicate that reduced sulphur from atmospheric influx is partially stored in the bark and may not be allocated to the root.