Abstract
The use of citric acid (CA) chelator to facilitate metal bioavailability is a promising approach for the phytoextraction of heavy metal contaminants. However, the role of the CA chelator associated with arbuscular mycorrhizal fungi (AMF) inoculation on phytoextraction of vanadium (V) has not been studied. Therefore, in this study, a greenhouse pot experiment was conducted to evaluate the combined effect of CA chelator and AMF inoculation on growth performance and V phytoextraction of plants in V-contaminated soil. The experiment was performed via CA (at 0, 5, and 10 mM kg-1 soil levels) application alone or in combination with AMF inoculation by Medicago sativa Linn. (M. sativa). Plant biomass, root mycorrhizal colonization, P and V accumulation, antioxidant enzyme activity in plants, and soil chemical speciation of V were evaluated. Results depicted (1) a marked decline in plant biomass and root mycorrhizal colonization in 5- and 10-mM CA treatments which were accompanied by a significant increased V accumulation in plant tissues. The effects could be attributed to the enhanced acid-soluble V fraction transferring from the reducible fraction. (2) The presence of CA significantly enhanced P acquisition while the P/V concentration ratio in plant shoots and roots decreased, owing to the increased V translocation from soil to plant. (3) In both CA-treated soil, AMF-plant symbiosis significantly improved dry weight (31.4-73.3%) and P content (37.3-122.5%) in shoots and roots of M. sativa. The combined treatments also showed markedly contribution in reduction of malondialdehyde (MDA) content (12.8-16.2%) and higher antioxidants (SOD, POD, and CAT) activities in the leaves. This suggests their combination could promote growth performance and stimulate antioxidant response to alleviate V stress induced by CA chelator. (4) Taken together, 10 mM kg-1 CA application and AMF inoculation combination exhibited a higher amount of extracted V both in plant shoots and roots. Thus, citric acid-AMF-plant symbiosis provides a novel remediation strategy for in situ V phytoextraction by M. sativa in V-contaminated soil.
Highlights
Vanadium (V) is a transition metallic element and widely distributed in the lithosphere (Hao et al, 2018)
Addition of citric acid (CA) treatment significantly reduced dry weight of plant shoot (17.0-27.4%) and root (26.2–37.1%), regardless of the existence of arbuscular mycorrhizal fungi (AMF) inoculation. This decrease on plant dry weight was associated with increased CA concentration, suggesting CA chelator at concentration of 5- and 10-mM kg− 1 soil showed some inhibitory effect on plant growth
We firstly demonstrated that the combined CA application and AMF inoculation treatment had more pronounced promotion in extracted amount of V in M. sativa, accompanied by good growth performance and enhanced antioxidant enzyme activities against V stress (Table 4), suggesting this combination could be recommended for assisting V-phytoextraction in the studied site
Summary
Vanadium (V) is a transition metallic element and widely distributed in the lithosphere (Hao et al, 2018). High concentration in soil and water environments can lead to detrimental effect on plant growth and all living organisms, it in trace amounts is an essential for human beings and animals (Crans et al, 2004; Yang et al, 2017). The United Nations Environment Programme (UNEP) has put vanadium on the priority list of environmental hazardous elements in 1980s (Hindy, 1990). The characteristics of nutrient deficiency, extreme pH, and decreased microbial diversity, accompanied in V mining contaminated soil, cause an impoverished habitat hindering plant establishment (Xiao et al, 2015). It is urgent to develop sustainably and economically efficient techniques for remediation of vanadium polluted sites
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