# The Suitability of Short Rotation Coppice Crops for Phytoremediation of Urban Soils
## 3 Results and Discussion
### Biomass Production  
All the genus tested showed good adaptation to the particular environment. Rooting of trees was complete for all the genotypes employed. Survival rate after the first three months was very high (97% on average), ranging from the 94% of R3, to the 100% of P1 and S2. The differences between genotypes do not reach statistical significance (ANOVA test, \(p=0.05\)). Complete data are reported in SM, Tables S2 and S3. Total biomass productions calculated for one hectare (10,000 plants) for both annual and biennial coppicing methods are reported in Table 3. The equations utilized for aboveground biomass estimation, calculated as reported in the Methods section, are reported in Supplementary Materials (SM). At the end of the first year, the best productions were achieved by _Robinia_ genotypes in both tests, statistically higher than other species, particularly by R1 with 0.75 t ha\({}^{-1}\) of dry matter (Table 3). _Robinia_ was able to withstand a limited water stress, maybe thanks to its symbiosis with nitrogen- fixing bacteria, as shown also from previous studies in the same climate, although on a non- polluted area [29]. _Poplar_ and _Salix_ gave yields not statistically different from each other (at \(p=0.05\)), probably due to water scarcity in the field, as from previous studies in northern Italy with fertilized and irrigated soil, poplars are usually more productive [29; 37]. The results were, however, in line with productions made on marginal areas and on contaminated soils [13; 17]. In this case, to maximally limit the management of the parcels it was chosen not to irrigate the field unless in the case of extreme drought. Three irrigations were performed during the first year and none during the second. At the end of the second year both the blocks with annual and biennial coppicing were harvested. During the whole experiment no symptoms of suffering due to excess of pollutants were detected. The most productive genus was the _Robinia_, with an average production around 4 t ha\({}^{-1}\), significantly higher than other species. High yield differences were obtained in all species between genotypes, reflecting the importance in the choice of species suitable to remediate mixed pollution sites but also of the need of a cultivar adapted to the climatic and contamination settings [38]. Genus respond in a different way to coppicing (Table 3); _Poplar_ clones were the only ones producing higher biomass during the second year after being coppiced at the end of the first vegetative season. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Genus**} & \multirow{2}{*}{**Genotype**} & \multicolumn{2}{c}{**Annual**} & \multicolumn{2}{c}{**Biennial**} \\ \cline{3-5}  & & **1 year** & **2 year** & **2 year** \\ \hline _Poplar_ & P1 & 340 (59) & 3335 (29) & 2587 (174) \\  & P2 & 210 (111) & 2447 (42) & 1643 (28) \\  & P3 & 204 (15) & 1228 (50) & 1606 (96) \\ _Salix_ & S1 & 262 (19) & 1360 (80) & 2641 (210) \\  & S2 & 178 (24) & 684 (11) & 1440 (135) \\  & S3 & 313 (53) & 1178 (23) & 2671 (112) \\ _Robinia_ & R1 & 754 (164) & 2684 (37) & 4922 (507) \\  & R2 & 437 (3) & 2274 (67) & 3290 (183) \\  & R3 & 456 (58) & 3597 (144) & 4153 (368) \\ \hline Average & & & & \\ \hline \multirow{5}{*}{_Robinia_} & _Poplar_ & 2592 \(\pm\) 1132 **a** & 1945 \(\pm\) 556 **a** \\  & _Salix_ & 1321 \(\pm\) 409 **a** & 2251 \(\pm\) 702 **a** \\  & _Robinia_ & 3395 \(\pm\) 672 **b** & 4122 \(\pm\) 816 **b** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Biomass production at the end of the 1 st and 2 nd year for each genotype. Average values for blocks (standard deviation) and for species, as dry biomass (in kg per hectare). Different bold letters represent statistical differences (\(p=0.05\)). _Salix_ and _Robinia_ produced higher biomass in blocks not coppiced. Due to the high variability between clone production differences between coppicing managements were not statistically significant. The most productive genotype was the R1 considering biennial coppicing, and R3 in annual coppicing.