SALT ACCUMULATION AND EFFECTS WITHIN FOLIAGE OF TILIA X VULGARIS TREES
FROM THE STREET GREENERY OF RIGA, LATVIA
Abstract
Green infrastructures within sprawling cities provide essential
ecosystem services, increasingly undermined by environmental stress. The
main objective in this study was to relate the allocation patterns of
NaCl contaminants to injury within foliage of lime trees mechanistically
and distinguish between the effects of salt and other environmental
stressors. Using field material representative of salt contamination
levels in the street greenery of Riga, Latvia, the contribution of salt
contaminants to structural and ultrastructural injury was analyzed,
combining different microscopy techniques. On severely salt-polluted and
dystrophic soils, the foliage of street lime trees showed foliar
concentrations of Na/Cl up to 13600/16750 mg kg-1 but a still balanced
nutrient content. The salt contaminants were allocated to all leaf blade
tissues and accumulated in priority within mesophyll vacuoles, changing
the vacuolar ionic composition at the expense of especially K and Ca.
The size of mesophyll cells and vacuoles was increased as a function of
NaCl concentration, suggesting impeded transpiration stream. In
parallel, the cytoplasm showed degenerative changes, suggesting indirect
stress effects. Hence, the lime trees in Riga showed tolerance to the
dystrophic environmental conditions enhanced by salt pollution but their
leaf physiology appeared directly impacted by the accumulation of
contaminants within foliage.