Interaction Between Atmospheric and Pedospheric Sulfur Nutrition in Eucalyptus camaldulensis

Plants are able to use gaseous sulfurous air pollutants as a sulfur source for growth, especially under circumstances where the sulfur supply to the roots is limited. In Eucalyptus camaldulensis seedlings there was a direct interaction between atmospheric H2S exposure and the uptake of sulfate by the root. At an ample sulfate supply, exposure of E. camaldulensis to 0.2 mu l l(-1) H2S for 1 week resulted in a decrease of the sulfate uptake capacity of the root (up to 70%). Sulfate deprivation resulted in an up to sixfold increase in the sulfate uptake capacity of the root, however, it was completely alleviated upon H2S exposure. At all conditions, the sulfate uptake capacity was strongly related to the sulfate concentration in the root. Evidently, upon H2S exposure E. camaldulensis transferred from sulfate taken up by the root to sul fi de absorbed by the shoot as sulfur source for growth. Despite that down-regulation of the sulfate uptake capacity occurred upon H2S exposure there was no direct metabolic control of the uptake and utilization of foliarly absorbed H2S. H2S exposure resulted in enhanced levels of total and organic sulfur (and nitrogen) in the shoot, whereas the N/S ratio strongly decreased.