Arboriculture & Urban Forestry 42(5): September 2016 339 Table 3. Foliar deposition, per unit leaf area and per the whole canopy, of six shrub species of five trace metals (Cd, Cu, Ni, Pb, and Zn). Data are the mean of three samplings performed in June, August, and October. Data are means ± SD. ANOVA tests (A) of differences between species are also included. Values as 0.000 are less than 0.001. V. lucidum Cd Cu Ni Pb Mean SD A 0.05 81.4 14.8 2.37 Zn 92.3 0.06 a 83.7 a 17.7 a 1.35 ab 82.4 a Cd Cu Ni Pb Mean SD A 0.00 4.08 0.74 0.11 Zn 4.62 A. unedo Mean SD A 0.04 96.4 17.1 1.62 140 0.05 a 109 a 17.5 a 1.25 bc 131 a 0.00 a 4.20 b 0.89 b 0.07 ab 4.13 b Mean SD A 0.00 3.84 0.68 0.06 5.60 P. × fraseri Mean SD A 0.03 70.1 11.8 1.89 114 0.04 a 65.6 a 13.1 a 0.96 abc 127 a 0.00 a 4.35 b 0.70 b 0.05 bc 5.23 b Mean SD A 0.00 3.91 0.66 0.11 6.37 L. nobilis Depositions per unit leaf area (µg cm-2 116 25.1 1.25 182 0.06 a 158 a 31.7 a 1.03 c 201 a Depositions on the whole plant (mg) 0.00 a 3.66 b 0.73 b 0.05 ab 7.06 b Mean SD A Mean SD A Mean SD A F 0.00 3.06 0.73 0.03 5.30 0.00 a 4.48 b 0.92 b 0.03 c 5.85 b 0.01 10.1 2.30 0.16 15.5 0.01 a 11.6 a 2.51 a 0.10 a 14.6 a 0.00 2.45 0.57 0.10 5.13 0.00 2.22 0.59 0.03 5.17 a b b b b P 0.44 2.46 3.16 5.53 3.08 0.82 0.04 0.01 0.00 0.02 Table 4. Partial least square regression analysis (PLSR) coefficients showing how deposition of different metals depends on wind velocity (Wind), air temperature (Air T°), relative humidity (RH%), and precipitation (Prec.). Values as 0.000 are not equal to 0 but less than 0.001. F Cd Cu Ni Pb Zn 10.74 34.41 19.98 3.24 128.18 P 0.002 0.000 0.000 0.077 0.000 r² 15 53 40 5 67 (Herms and Mattson 1992). Under these condi- tions, the planting of profligate/opportunistic spe- cies with a high assimilation rate is highly advisable because they allow maximization of both CO2 assimilation and growth. Among the species stud- ied here, E. × ebbingei and L. nobilis outperformed the others under non-limiting moisture in terms of carbon uptake and growth. In detail, E. × ebbingei showed the highest CO2 assimilation rates per unit leaf area throughout the day, and particularly dur- ing the aſternoon, when photosynthesis of most of the other species was greatly constrained by midday depression. Furthermore, this species, when grown with adequate moisture, can sustain these rates over a large leaf area, resulting in higher daily carbon uptake per individual plant compared to most of the other species investigated. On the contrary, other species, such as P. × fraseri and L. japonicum, had high CO2 assimilation rates but low total leaf area per growth rates compared to E. × ebbingei and L. nobilis. It must also be considered that, for a given plant, resulting in lower daily CO2 assimilation and increase in plant biomass, species that invest more in leaves than in woody biomass store carbon for a shorter period, particularly in the urban environ- ment where fallen leaves are artificially removed Const. -0.000 -0.732 -0.121 -0.001 -1.159 Wind 0.000 0.486 0.086 0.002 0.801 Air T° 0.000 0.048 0.007 0.000 0.071 RH% -0.000 -0.009 -0.001 -0.000 -0.012 Prec. -0.000 -0.001 -0.000 -0.000 -0.002 Table 5. Clusters derived from cluster analysis and fac- tor loadings of two factors identified from factor analysis for metals on leaves during the entire sampling period. Varimax rotation was applied to factor analysis. Cd Cu Ni Pb Zn Cluster 2 1 1 2 2 Factor 1 0.25 0.97 0.96 -0.02 0.88 Factor 2 0.83 0.09 0.01 0.89 0.28 (Nowak et al. 2002). Therefore, species such as V. lucidum, with a high carbon allocation to leaves, may not be advisable for maximizing carbon storage. Drought stress reduces plant carbon gain by act- ing on both stomatal and mesophyll conductance, and affecting the activity of Rubisco and the rate of ribulose regeneration (Chaves et al. 2002; Medrano et al. 2002). Furthermore, drought can alter photo- synthate partitioning to primary (growth) and sec- ondary (defense) metabolism, thereby decreasing the amount of assimilated carbon stored as woody biomass. For example, in a recent experiment, when shrubs of the isoprene emitter species Platanus × acerifolia were moved from a moist to a dry envi- ronment, the amount of photosynthate allocated to isoprene (a defense compound) was unchanged, ©2016 International Society of Arboriculture E. × ebbingei *1000) Mean SD A Mean SD A Mean SD A F 0.04 0.03 108 24.4 2.09 164 0.05 a 123 a 26.6 a 0.72 ab 155 a 0.03 69.6 18.0 2.55 146 0.05 56.2 14.9 0.75 133 a a a a a P 0.31 0.83 1.02 3.71 2.33 0.90 0.55 0.44 0.02 0.09 L. japonicum
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