Effects of heavy metal pollution on oak leaf microorganisms

During the growing season, comparisons were made of the leaf surface microflora of (i) two groups of mature oak trees, one in the vicinity of a smelting complex contaminated by heavy metals and the other at a relatively uncontaminated site, and (ii) two groups of oak saplings at the uncontaminated site, one of which was sprayed with zinc, lead, and cadmium to simulate the heavy metal pollution from the smelter without the complicating effects of other pollutants. Total viable counts of bacteria, yeasts, and filamentous fungi (isolated by leaf washing) were generally little affected by the spraying treatment, whereas polluted leaves of mature trees supported fewer bacteria compared with leaves of mature trees at the uncontaminated site. Numbers of pigmented yeasts were lower on polluted oaks and on metal-dosed saplings compared with their respective controls. Polluted leaves of mature trees supported both greater numbers of Aureobasidium pullulans and Cladosporium spp. and a greater percentage of metal-tolerant fungi compared with oak leaves at the uncontaminated site. There were no significant overall differences in the degree of mycelial growth between the two groups of saplings or the mature trees.