334 Mori et al.: Carbon Uptake and Air Pollution Mitigation of Different Evergreen Shrub Species tions (Exp. 3) were tested with repeated mea- sures ANOVA and separation of the means was carried out using Duncan’s MRT (CoStat 6.303, CoHort Software, Monterey, California, U.S.). The relationships between metal depositions on leaves and climate parameters were tested using Partial Least Square Regression (PLSR) for each metal separately. PLSR is useful when a high level of multi-collinearity among the explanatory variables is assumed (Rosipal and Trejo 2001). Correlations between the deposited metals were tested using Pearson product-moment correla- tion coefficients (r) and only the r values above 0.5 were considered. Multivariate methods were used to identify the possible sources of different metals. Cluster Analysis (CA) was performed using Ward’s method and Euclidean distance as metric (Oliva and Espinosa 2007). Factor Analysis (FA) was accomplished with Varimax rotation (Lorenzini et al. 2006). The outliers were identified and removed from the data set. RESULTS Experiment 1: Carbon Uptake Under Optimal Water Availability Elaeagnus × ebbingei, A. unedo, and L. nobilis had the highest mean daily CO2 est woody biomass production (data not shown) and the highest over the experimental period (Figure 2C). A positive strong correlation (P < 0.01; R2 Laurus nobilis and E. × ebbingei gave the high- relative growth rate calculated = 0.95) lation and relative growth rate (Figure 2D). Allocation of photosynthates among plant organs was found between whole-plant CO2 differed across species. V. lucidum allocated more carbon to leaves compared to all other species. On the contrary, V. tinus, E. × ebbingei, and L. japoni- cum displayed lower percentages of C allocation to leaves compared to the other species considered, even if differences were significant only when com- pared to V. lucidum (Figure 3). At the end of the experiment, E. × ebbingei, L. nobilis, V. lucidum, and V. tinus had higher total leaf area (0.29 ± 0.05; 0.32 ± 0.04; 0.27 ± 0.04; 0.30 ± 0.05 m2 than A. unedo, P. × fraseri, and L. japonicum (0.18 ± 0.03; 0.19 ± 0.05; 0.16 ± 0.05 m2 , respectively) , respectively). assimilation per unit eter that considers both the assimilation per unit leaf area and the total leaf area of the plant) was higher in E. × ebbingei and L. nobilis than in V. lucidum, V. tinus, and P. × fraseri; A. unedo and L. japonicum showed the lowest values (Figure 2B). Species had different WUE (V. lucidum = 3.87 values similar to those in the morning, aſter 3:00 pm. CO2 ± 2.35; A. unedo = 3.93 ± 1.86; P. × fraseri = 4.71 ± 2.51; L. nobilis = 4.86 ± 2.14; E. × ebbingei = 4.76 ± 2.34; L. japonicum = 4.09 ± 2.06 ; V. tinus = 4.36 ± 2.60 expressed as µmol CO2 mmol-1 ©2016 International Society of Arboriculture H2 O). morning hours and then underwent a significant midday depression. Elaeagnus × ebbingei and L. ja- ponicum, in contrast with the other species, showed a significant recovery of CO2 assimilation, reaching assimilation of the whole plant (a param- leaf area compared to the other species when shrubs were grown under optimal water availability (Figure 2A). Conversely, V. lucidum, L. japonicum, and V. tinus showed the lowest values. All species showed the highest values of CO2 assimilation during the Experiment 2: Carbon Uptake and Storage Under Drought Stress On average, substrate moisture of WS shrubs declined to 15% of its holding capacity by the end of “drought phase 1” (T-3), where it was main- tained around 30% by irrigation until T-4 and finally declined to 12% at the end of “drought phase 2” (T-5) (Figure 4A). CO2 assimilation of WW shrubs largely confirmed the values observed in Experiment 1 (data not shown) and did not statistically differ from data collected from WS shrubs at T-0. As drought progressed (T-1,T-2, T-3), CO2 of some species (i.e., P. × fraseri, V. tinus, L. ja- ponicum) exhibited some recovery, while in other species (i.e., E. × ebbingei, A. unedo, V. lucidum) CO2 edo. During partial relief (T-4), CO2 fraseri, V. tinus, and L. japonicum had higher CO2 assimilation than E. × ebbingei and V. lucidum. However, as drought progressed, CO2 assimilation of E. × ebbingei was strongly reduced (Figure 4B). A similar trend was found in V. lucidum, which assimilation than V. tinus and A. un- assimilation assimi- assimilation declined in all species, but the magnitude of the decline was species-specific, with species such as E. × ebbingei and V. lucidum experiencing greater drought-induced reductions in CO2 assimilation showed little or no recovery. At the end of drought phase 2 (T-5), A. unedo, P. ×
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