is a metal excluder, with an extensive root system, a relatively large biomass, and a lowroot-to-shoot metal translocation, suggested as a suitable species for metal phytostabilization (Barrutia et al., 2011; Epelde et al., 2010). Furthermore, F. rubra is the dominant plant species in the study area, thus proving its capacity to tolerate high metal concentrations and a shortage of soil nutrients. In vegetated sites (V1 and V2), all amendments led to higher values of the F. rubra relative biomass index (Table 3), and most likely due to the supply of nutrients from the amendments. In any case, highest values of the F. rubra relative biomass index were observed in POULTRY-treated plots. As stated above, the dose of amendment was adjusted to add the same N amount (a most important element for soil fertility and plant growth) in all treatments; this stimulatory effect was more pronounced in site V2, despite showing higher total and CaCl
-extractable metal concentrations than those in site V1 (Table 1). A similar response was observed for the values of plant relative growth rate, which were higher at 2 months versus 6 months: in general, higher values were observed in treated than control plots, and in POULTRY-treated versus all the other plots (Table S1). On the other hand, in initially non-vegetated sites (NV1 and NV2), at the end of the experiment, the vegetation cover (%) increased in alltreated plots, with highest values for POULTRY-treated plots (Table 3). Nitrogen mineralization from amendments and subsequent N uptake by F. rubra plants have most likely played an important role in the observed increase in plant biomass and cover. Hartz et al. (2000) observed 3–4 times higher rates of N mineralization and 2–3 times higher rates of total N recovery by Festuca arundinacea plants in dewatered poultry
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