Effects of calcium on nickel tolerance and accumulation in Alyssum species and cabbage grown in nutrient solution

Abstract

Nickel (Ni) phytoextraction using hyperaccumulator plant species to accumulate Ni from mineralized and contaminated soils rich in Ni is undergoing commercial development. Serpentinite derived soils have a very low ratio of Ca/Mg among soils due the nature of the parent rock. In crop plants, soil Ca reduces Ni uptake and phytotoxicity, so it is possible that the low Ca of serpentine soils could limit hyperaccumulator plant tolerance of serpentine soils used for commercial phytomining. In this study, we investigated the effects of varied Ca concentration in the presence of high Mg characteristic of serpentine soils on Ni uptake and tolerance by serpentineendemic species Alyssum murale Waldst. et Kit. and A. pintodasilvae T.R. Dudley in comparison with cabbage (Brassica oleracea L. var. capita) in a nutrient solution study. The levels of Ca and Mg used were based on serpentine and normal soils, and Ni was based on achieving over 1% Ni in Alyssum shoots in preliminary tests. Varied solution concentrations of Ni (31.6-1,000 μM for Alyssum, 1.0-10 μM for cabbage) and Ca (0.128-5 mM) were used in a factorial experimental design; 2 mM Mg was used to mimic serpentine soils. Alyssum spp. showed much greater tolerance to high Ni, high Mg, and low Ca solution concentrations than cabbage. For Alyssum spp., Ni induced phytotoxicity was only apparent at 1,000 μM Ni with relatively low and high Ca/Mg quotient. In the 1,000 μM Ni treatment, shoot Ni concentrations ranged from 8.18 to 22.8 g kg −1 for A. murale and 7.60 to 16.0 g kg −1 for A. pintodasilvae. Normal solution Ca concentrations (0.8-2 mM) gave the best yield across all Ni treatments for the Alyssum species tested. It was clear that solution Ca levels affected shoot Ni concentration, shoot yield and Ni translocation from root to shoot, but the relation was non-linear, increasing with increasing Ca up to 2 mM Ca, then declining at the highest Ca. Our results Plant Soil (indicate that Ca addition to high Mg serpentine soils with very low Ca/Mg ratio may reduce Ni phytotoxicity and improve annual Ni phytoextraction by Alyssum hyperaccumulator species. Removal of shoot biomass in phytomining will require Ca application to maintain full yield potential.

Current status and challenges in developing nickel phytomining: an agronomic perspective

“…The Ni content of B. coddii increased two-fold with N addition (Robinson et al 1997a), whilst split N application also increased annual biomass Ni yields (Bani et al 2015a;Chaney et al 2007a). Phosphorus has a particularly strong effect on the biomass yield and Ni uptake by hyperaccumulator species growing on soil not previously fertilized (Table 3) while previously fertilized soils show a lesser response to P fertilizer (Bennett et al 1998;Chaney et al 2008;Robinson et al 1997a;Shallari et al 2001). Additions of micronutrients have also been considered during fertilisation trials because ultramafic soils are usually deficient in B and Mo (Li et al 2003b).…”

“…Studies show that there is a positive correlation between the exchangeable Ca:Mg ratio and the labile Ni pools in ultramafic soils (Cheng et al 2011). Calcium supply to high Mg ultramafic soils will be required to maintain the annual Ni uptake in Alyssum species because biomass harvest and removal reduces the pool of phytoavailable Ca in these soils, for example, the annual removal of 1 t of biomass removes 20 kg of Ca (Chaney et al 2007a;Chaney et al 2008). The sequestration mechanisms for Ni is distinct from Ca handling or storage in Ni hyperaccumulator plants (Broadhurst et al 2004a); but a positive correlation exists in the foliar concentrations of Ca and Ni in some 'metal crop' species (van der Ent and Mulligan 2015).…”

“…Nickel hyperaccumulator species absorb more Ca relative to Mg, which leads to high Ca:Mg ratio in the leaf tissues (Bani et al 2014); this selective Ca accumulation from soils with very low Ca:Mg ratios substantially reduces Mg and Ni toxicity (Kruckeberg 1991). Unless Ca is actually deficient, Ca addition has little effect on the Ni concentration in the above-ground biomass and shoot yield as well as root-to-shoot translocation of Ni, but may increase Ni tolerance (Chaney et al 2008). Calcium supply in the form of CaCO 3 increases Ni uptake in hyperaccumulator plants growing on some soils, as a result of the combined effect of Ca addition and soil pH (Kukier et al 2004).…”

Accumulation of some heavy metals in plants and soils adjacent to Cairo – Alexandria agricultural highway

“…Also, soil Ca might minimize Ni uptake by plant roots thus reduces its toxicity (Chaney et al, 2008 andYusuf et al, 2011). …”

Plant diversity and foliar elemental profiles in relation to soil chemistry and altitude on ultramafic edaphic islands in Kinabalu Park (Malaysia)

“…Soil Ni sorption to smectite clay (montmorillonite) in the presence of low concentrations of citrate is reduced by 50-90% (Poulsen and Hansen, 2000;Marcussen et al, 2009) (Yamaguchi et al, 2002). Given that citrate is the predominant Ni-binding ligand in tropical Ni hyperaccumulators (Callahan et al, 2006;2008;, the release of citrate by hyperaccumulator roots could be highly effective in mobilizing of Ni-toxicity (Gabrielli and Pandolfini, 1984;Robertson, 1985;Heikal et al, 1989;Chaney et al, 2008), through the reduction of ion activity (Becquer et al, 2010) and by competition for Ni adsorption on soil sorption sites. This could explain the high phytoavailability of Ni, and hence potential uptake, in these soils.…”