Salinity and Heavy Metal Tolerance, and Phytoextraction Potential of Ranunculus sceleratus Plants from a Sandy Coastal Beach

Abstract

The aim of the present study was to evaluate tolerance to salinity and different heavy metals as well as the phytoextraction potential of Ranunculus sceleratus plants from a brackish coastal sandy beach habitat. Four separate experiments were performed with R. sceleratus plants in controlled conditions: (1) the effect of NaCl gradient on growth and ion accumulation, (2) the effect of different Na+ and K+ salts on growth and ion accumulation, (3) heavy metal tolerance and metal accumulation potential, (4) the effect of different forms of Pb salts (nitrate and acetate) on plant growth and Pb accumulation. A negative effect of NaCl on plant biomass was evident at 0.5 g L−1 Na+ and growth was inhibited by 44% at 10 g L−1 Na+, and this was associated with changes in biomass allocation. The maximum Na+ accumulation (90.8 g kg−1) was found in the stems of plants treated with 10 g kg−1 Na+. The type of anion determined the salinity tolerance of R. sceleratus plants, as Na+ and K+ salts with an identical anion component had a comparable effect on plant growth: nitrates strongly stimulated plant growth, and chloride treatment resulted in slight but significant growth reduction, but plants treated with nitrites and carbonates died within 4 and 5 weeks after the full treatment, respectively. The shoot growth of R. sceleratus plants was relatively insensitive to treatment with Mn, Cd and Zn in the form of sulphate salts, but Pb nitrate increased it. Hyperaccumulation threshold concentration values in the leaves of R. sceleratus were reached for Cd, Pb and Zn. R. sceleratus can be characterized as a shoot accumulator of heavy metals and a hyperaccumulator of Na+. A relatively short life cycle together with a high biomass accumulation rate makes R. sceleratus useful for dynamic constructed wetland systems aiming for the purification of concentrated wastewaters.

Ranunculus sceleratus as a Model Species to Decrypt the Role of Ethylene in Plant Adaptation to Salinity

“…However, in contrast to the effect on Na + concentration, which was prevented by MCP treatment, the inhibitory effect of ethylene on K + accumulation was not fully prevented by MCP. An ability to retain adequate K + concentration in salt-stressed plant tissues has been associated with salinity tolerance for glycophytic species [ 16 , 41 ], but Na + can replace K + for osmotic functions in halophytes [ 31 , 42 , 43 ]. Therefore, ethylene-dependent decreases in the K + concentration could not have any negative consequences in R. sceleratus .…”

“…Plants were established from seeds produced in controlled conditions from a seed material initially collected in natural habitat of seawater-affected, wet, and sandy beach in Salacgrīva, Latvia [ 31 ]. Detailed procedure for plant establishment and cultivation is described previously [ 31 ].…”

“…Plants were established from seeds produced in controlled conditions from a seed material initially collected in natural habitat of seawater-affected, wet, and sandy beach in Salacgrīva, Latvia [ 31 ]. Detailed procedure for plant establishment and cultivation is described previously [ 31 ]. Briefly, seeds were germinated in autoclaved commercial garden soil (Biolan, Eura, Finland) in plastic tissue culture containers for 20 days in a plant growth cabinet, then transplanted to 0.2 L plastic containers filled with mixture of garden soil and quartz sand (Saulkalne S, Saulkalne, Latvia) 1:3 ( v / v ), and were adapted to greenhouse conditions: automated greenhouse (HortiMaX, Maasdijk, The Netherlands) with supplemented light that was provided by Master SON-TPIA Green Power CG T 400 W (Philips, Amsterdam, The Netherlands) and Powerstar HQI-BT 400 W/D PRO (Osram, Munich, Germany) lamps (photon flux density of photosynthetically active radiation 380 µmol m –2 s –1 at the plant level), for a 16 h photoperiod, at a day/night temperature of 22/15 °C, with a relative air humidity of 60–70%.…”

“…Dried plant material was used for measurement of Na + and K + concentration and electrical conductivity (EC) using LAQUAtwin compact meters B-722 (Na + ) and B-731 (K + ), and LAQUAtwin conductivity meter B-771 (Horiba, Kyoto, Japan), as described previously [ 31 ]. Six individual samples per treatment were independently measured.…”

“…The species has been used as a model for studies of ethylene-dependent flooding-induced leaf petiole elongation [ 30 ]. Recently, an accession of R. sceleratus from a brackish coastal beach habitat was characterized as having a good tolerance to heavy metals and salinity and showed a high shoot metal accumulation capacity [ 31 ]. The aim of the present study was to develop an experimental system for the exploration of ethylene-dependent responses using intact growing R. sceleratus plants and to approbate the system for assessing the role of ethylene in ion accumulation under saline conditions.…”