Abstract
Salicornia ramosissima is a C3 halophyte that grows naturally in South Western Spain salt marshes, under soil salinity and heavy metal pollution (mostly Cu, Zn, As, and Pb) caused by both natural and anthropogenic pressure. However, very few works have reported the phytoremediation potential of S. ramosissima. In this work, we studied a microbe-assisted phytoremediation strategy under greenhouse conditions. We inoculated plant growth promoting (PGP) and heavy metal resistant bacteria in pots with S. ramosissima and natural non-polluted and polluted sediments collected from Spanish estuaries. Then, we analyzed plant ecophysiological and metal phytoaccumulation response. Our data suggested that inoculation in polluted sediments improved S. ramosissima plant growth in terms of relative growth rate (RGR) (32%) and number of new branches (61%). S. ramosissima photosynthetic fitness was affected by heavy metal presence in soil, but bacteria inoculation improved the photochemical apparatus integrity and functionality, as reflected by increments in net photosynthetic rate (21%), functionality of PSII (Fm and Fv/Fm) and electron transport rate, according to OJIP derived parameters. Beneficial effect of bacteria in polluted sediments was also observed by augmentation of intrinsic water use efficiency (28%) and slightly water content (2%) in inoculated S. ramosissima. Finally, our results demonstrated that S. ramosissima was able to accumulate great concentrations of heavy metals, mostly at root level, up to 200 mg Kg–1 arsenic, 0.50 mg Kg–1 cadmium, 400 mg Kg–1 copper, 25 mg Kg–1 nickel, 300 mg Kg–1 lead, and 300 mg Kg–1 zinc. Bioaugmentation incremented S. ramosissima heavy metal phytoremediation potential due to plant biomass increment, which enabled a greater accumulation capacity. Thus, our results suggest the potential use of heavy metal resistant PGPB to ameliorate the capacity of S. ramosissima as candidate for phytoremediation of salty polluted ecosystems.
Highlights
Environmental pollution has become a major public concern over the last century
This work aimed at (1) assessing the tolerance to heavy metals of the bacteria selected for inoculation, in order to ensure they can be used in polluted sediments, (2) describing heavy metal accumulation capacity of S. ramosissima growing in natural salt marsh sediments, and (3) analyzing S. ramosissima response to plant growth promoting bacteria (PGPB) inoculation in terms of growth, photosynthetic fitness, and metal accumulation
Bacteria selected in this work for bioaugmentation treatments were Vibrio neocaledonicus SRT1, Thalassospira australica SRT8, and Pseudarthrobacter oxydans SRT15
Summary
Heavy metal content in water and soil has increased due to rapid worldwide industrial development (Usman et al, 2018). This problem is further compounded by soils simultaneously affected by salinity because of climate change and irrigated agriculture (Liang et al, 2017). Phytoremediation strategy is based on major plants, and on associated microbes and their processes In this sense, plant growth promoting bacteria (PGPB) bioaugmentation has been proposed as a strategy to improve innate heavy metal phytoremediation capacity in halophytes, since it has been proven to ameliorate plant growth, stress tolerance and phytoremediation potential (Backer et al, 2018). Positive results have been recently obtained for Spartina, Arthrocnemum, and Suaeda species, which incremented their root metal phytoaccumulation capacity when they were PGPB-treated (Mateos-Naranjo et al, 2015; Mesa et al, 2015b; Navarro-Torre et al, 2017a; Gómez-Garrido et al, 2018)
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