From lava to leaf: Physiological responses and trace element mobility in Tilia cordata L. trees grown in volcanic ash amended urban soil

This study investigates the potential of utilizing volcanic ash (VA), classified as special waste, as an inorganic soil amendment to enhance tree growth and resilience in urban areas near volcanic regions. Lime trees were transplanted into pots filled with urban soil (Cnt) or amended with 10 % VA. Tree's physiological traits were monitored over the growing season. Notably, VA-treated trees showed improved net CO2 2 assimilation (Pn) n ) and stomatal conductance (gs) s ) during the leaf senescent stage. The analysis of ash, and Cnt and VA soils, showed low concentrations of trace elements. In addition, trace element accumulation in the leaves of VA trees was not observed. In summer, during a 12-day drought stress test, VA-stressed trees exhibited enhanced water absorption, reduced lipid peroxidation, and higher Pnand n and gs s values in the initial days compared to control-stressed trees. Importantly, the VA also promoted a 33 % larger tree root system, potentially enhancing drought resilience. This could offer an important advantage for trees, especially during the tree's critical establishment phase. Thus, VA could be a promising amendment for urban soils to bolster tree tolerance to drought.