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Physiological response of Populus balsamifera and Salix eriocephala to salinity and hydraulic fracturing wastewater for potential in phytoremediation Bilek, Michael


Agriculturally productive land is degrading at an alarming rate due to a rapidly increasing population affecting the extent of industrial pollution and soil salinization. It is estimated that more than 10% of global landmass is salt-affected, which results in lowered crop yield and disrupted local environments. Hydraulic fracturing (fracking), has recently seen increased frequency of use, but its environmental effects are poorly studied. This study examines the efficacy of Populus balsamifera L. and Salix eriocephala Michx. for their phytoremediation potential on saline and fracking wastewater polluted soils. Three growth trials were performed to screen for tolerance and quantify physiological responses to abiotic stress: a screening trial with thirty-one poplar and willow genotypes grown for eight weeks on 0, 30, and 80 mM NaCl, a second salinity trial with two poplar, five willow, and one hybrid willow genotypes grown for twelve weeks with 0, 20, 40, and 60 mM NaCl, and a fracking trial consisting of three willow and one hybrid willow genotypes treated for eight weeks with fracking wastewater dilutions. Poplar genotypes were susceptible to salinity, showing significant reductions in growth and failing to survive at 60 and 80 mM NaCl treatments. Poplar sensitivity is likely due to its inability to restrict sodium transport to aerial tissues. Native and hybrid willows did not experience mortality when grown at or below 60 mM NaCl treatments, and showed no reduction in height at 20 mM NaCl. Hybrid willow (Lev-13) accumulated the most biomass while native willow genotypes (Cam-2 and St-2) showed the smallest reductions in growth with increasing treatment. Water-use efficiency increased significantly with salinity treatment in native and hybrid willow genotypes. Stachyose and raffinose content tripled in leaf and root tissues respectively, suggesting use in oxidative defense. Tolerant willow genotypes excluded sodium iv from leaf tissues and maintained higher K:Na ratios. In the fracking wastewater trial, the two willow genotypes Cam-2 and St-2 displayed limited necrosis, resistance to biomass loss, and survived eight weeks of treatment, while the hybrid did not survive the highest treatment. These results identify two candidate native willow genotypes for further study and use in phytoremediation field-trials.

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