340 Mori et al.: Carbon Uptake and Air Pollution Mitigation of Different Evergreen Shrub Species despite a five-fold reduction of photosynthesis (Tattini et al. 2015). Clearly, if photosynthesis is impaired, secondary metabolism is fed by reserves that then become unavailable for growth (Loreto and Schnitzler 2010); the more the stress is perceived as severe by the plant, the more primary metabolism is likely to be affected. Finally, when a plant is killed by drought, the carbon stored in its woody organs will return to the atmosphere, unless the woody material is properly managed (i.e., soil amendment) (Nowak and Crane 2002). Therefore, when planting harsh sites with the aim of improving CO2 sequestration, it is necessary to plant species that are “horticul- turally tolerant”; that is, drought-tolerant species capable of sustaining carbon gain and growth under stressful conditions (see Fini et al. 2013), or their benefits will be greatly reduced or neglected. Species with conservative water use, such as the water shortage, as occurs in profligate/opportunistic species, usage of irradiance in the photosynthetic process is also reduced, and leaves may experi- ence severe excess light stress, leading to photo- inhibition and photo-oxidative damage (Chaves et al. 2008; Fini et al. 2012). The large drop in Fv/ Fm observed in E. × ebbingei, L. japonicum, and V. lucidum indicates that photo-inhibition probably occurred in leaves of these species during drought (Percival 2005; Kalaji et al. 2012; Fini et al. 2013). Although severe drought induced a decline high concentra- Mediterranean shrubs A. unedo and V. tinus, had lower stomatal conductance and carbon assimila- tion than profligate/opportunistic species under non-limiting water availability, but maintain rela- tively high leaf gas exchange during drought. The capacity of A. unedo and V. tinus to preserve the functionality of the photosynthetic apparatus dur- ing drought is confirmed by the lower decline in the maximum quantum yield of photosystem II (Fv/ Fm) compared to profligate/opportunistic species, such as E. × ebbingei, L. japonicum, and V. lucidum. When CO2 assimilation is largely constrained by carbon storage is a project goal, species with a prof- ligate/opportunistic water use and fast growth rate, such as E. × ebbingei and L. nobilis, should be planted in moist/irrigated planting sites, while species with a conservative water use or effective photoprotec- tive mechanisms (A. unedo, V. tinus, P. × fraseri) are recommended for drought-prone environments. A potential limitation of this study is that the life different shrub species per unit time, they may not reflect the total carbon stored over the whole life of the plant. However, with the exception of A. unedo, which can live for up to 400 years, the life span of the other shrub species is similar, ranging from 20 to 50 years (Clemson Cooperative Extension 2015; AUB Landscape Plant Database 2016; Euro- pean Trees 2016). In addition, all the three species (A. unedo, V. tinus, P. × fraseri) have similar size at maturity, ranging from 3 to 7 m (Brikell 2008). These life spans fit the normal turnover of green spans of the different species were not considered. Thus, while the results may be valuable for under- standing CO2 assimilation and carbon storage of areas in urban environments well, where plants oſten decline because of multiple stresses and are not likely to complete their life cycles (Kozlowski 1999). of photosynthesis, P. × fraseri displayed the lowest decline in Fv/Fm. The tion of anthocyanins in this red-leafed species may explain its notable capacity to counter excess light stress and avoid severe photo- inhibition during water stress (Tattini et al. 2015). In summary, the results of Experiments 1 and 2 assimilation and indicate that, if maximizing CO2 ©2016 International Society of Arboriculture Experiment 3: Leaf Deposition of Trace Metals Leaf deposition per unit leaf area of Pb differed among species, while for the other metals adsorp- tion was not affected by species. In addition, the species that showed the highest quantities of Pb (L. japonicum, V. lucidum, and E. × ebbingei) had no specific common characteristics (e.g., presence of leaf trichomes, high growth parameters) dif- ferentiating them from the other species (Table 6; Figure 7). Elaeagnus × ebbingei is the only spe- cies with a visible presence of trichomes that can be related to a higher capacity of pollutant reten- tion (Beckett et al. 2000). Ligustrum japonicum and V. lucidum, unlike the other species, showed the presence of secretory glands, especially on the lower leaf surface (Figure 8). Secretory activity is evident by the light color of the glands, indicat- ing of the presence of salts (Sakai 1974), which may be related to the higher values of Pb in the aforementioned species. Lavid et al. (2001) found that Pb may be excreted by leaves through epider- mal glands, and this is consistent with the limited
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