Carbon uptake and air pollution mitigation of different Evergreen shrub species

Three independent experiments assessed CO2 assimilation and metals leaf deposition of seven evergreen shrub species (Arbutus unedo L., Elaeagnus × ebbingei L., Laurus nobilis L., Ligustrum japonicum Thunb., Photinia × fraseri Dress., Viburnum tinus subsp. lucidum L., and Viburnum tinus subsp. tinus L.). CO2 assimilation and carbon allocation were determined in 2011 (Exp. 1) under optimal water availability and in 2012 (Exp. 2) under drought on potted plants. A third experiment (Exp. 3) measured seasonal leaf depositions of Cd, Cu, Ni, Pb, and Zn in 2011 on plants transplanted in proximity of a four-lane road. E. × ebbingei showed the highest CO2 assimilation under optimal water availability but one of the lowest under drought (Exp. 1, 2). Conversely, P. × fraseri had intermediate CO2 assimilation but it declined less during drought compared to the other species. In Experiment 3, E. × ebbingei showed the highest metal deposition, mainly due to its greater leaf area. Greater rainfall and RH% decreased metal depositions, whilst greater wind velocity and air temperature increased leaf depositions. Species which drastically reduce CO2 assimilation under drought (V. tinus subsp. lucidum, L. japonicum, E. × ebbingei) are not recommended in droughtprone environments, where drought-tolerant "mesic" species (P. × fraseri), should be preferred. E. × ebbingei could be used to optimize deposition of metals. The three experiments provide useful insights especially about CO2 assimilation (Exp. 1, 2) and air pollution mitigation (Exp. 3) of widely used shrubs for application in urban areas and planning of roadside greening in southern Europe.