Effects of elevation on growth, photosynthetic and Ni-accumulation responses in Bornmuellera emarginata (Brassicaeae)

Bornmuellera emarginata is a Balkan Ni-hyperaccumulator indicated as a promising candidate for agromining practices. Here, two elevation-contrasting accessions (250 m, Low Elevation plants LE, and at 1600 m, High Elevation plants, HE) were compared in terms of growth, photosynthetic activity, and Ni accumulation in controlled conditions to assess possible differences exploitable in practical applications. After two months of pot cultivation on garden and serpentine soil, plant biomass, gas exchanges and Ni concentrations were evaluated. A hydroponic trial with increasing NiSO4 concentration was performed to evaluate Ni tolerance and accumulation. Plants grown on serpentine soil showed reduced biomass as compared to those from garden soil, without any difference between LE and HE. In both accessions, growth in serpentine soil resulted in photochemical/biochemical limitations and reduction in stomatal conductance, especially in LE. HE showed low stomatal conductance in all the conditions, despite a greater stomatal density. Shoot Ni accumulation was higher in HE (similar to 1600 mu g Ni g(-1) d.w. and 1200 mu g Ni g(-1) d.w. in HE and LE respectively), thus resulting in a significantly higher metal content per plant in respect to LE (similar to 120 and similar to 85 mu g plant(-1) in HE and LE respectively). In hydroponics, HE possessed higher Ni tolerance and accumulation in respect to LE. In conclusion underlying the higher shoot metal amount of HE, Ni tolerance seemed to play a pivotal role, overtaking possible negative effects of reduced transpiration rates compared to LE. Our results point to the opportunity of exploring and exploiting the variation in accumulation level among B. emarginata accessions for the implementation of environmental restoration and metal cropping practices.