Effects of different shading levels on the growth of Bornmuellera emarginata, a nickel hyperaccumulator for use in agromining

The Greek endemic Bornmuellera emarginata, known for its Ni hyperaccumulation capacity, is a promising candidate species for use in agromining. At the same time, the installation of photovoltaic systems on agricultural land has recently been increasing. Field observations that populations of this species usually occupy shaded places under shrubs or trees led us to study the effect of different shading levels on the growth of B. emarginata, with a view to combine the cultivation of the species with photovoltaic panels in the same area. The experiment was conducted under greenhouse conditions and lasted 210 days after sowing (DAS). Seeds were sown directly into 2-L pots filled with ultramafic soil collected from the field. Three plant samplings (81, 140, and 210 DAS) were conducted during the experiment to determine a set of morphological and physiological parameters of the species (fresh and dry plant biomass, plant height, number of lateral shoots, total number of leaves, proline and chlorophyll concentrations) alongside with its nickel yield at different levels of shading (0%, 20%, 35%, 60%, and 90%). Growth of B. emarginata was only significantly affected at the highest shading level. Nickel yield of the species increased over time and was maximized at the end of the experiment. The highest nickel yield per plant was observed at the intermediate shading level (35%). Bornmuellera emarginata can be considered as a candidate nickel hyperaccumulator for cultivation in ultramafic or nickel-polluted areas under photovoltaic panels with corresponding shading, providing important environmental benefits.