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Dissecting ionic effects of soil salinity on Canadian native and hybrid willows (Salix spp.) Huang, Xinyi


Among all the stressors on global agricultural systems, soil salinity and salinization is arguably one of the most significant and an ever increasing problem. Traditionally, sodium chloride is the salt employed for studying salt stress in plants, but on the Canadian prairie regions, sulphates are the predominant salts that cause osmotic imbalance and specific ion toxicities, and subsequently induce oxidative damage in plants. Willows (Salix spp.) have been identified as potential candidate plants for multipurpose establishment on saline marginal fields. As a phytoremediation strategy, growing salt tolerant willows could improve biodiversity, quality, and productivity of soil and local ecosystems, while providing biomass production for a series of downstream agricultural and industrial applications. In order to investigate the salt tolerance among willows, and to dissect the ionic effects of different salt ions on plants, two greenhouse trials were conducted with mixed salt treatments in the first trial, as well as sodium and magnesium sulphate treatments in the second trial, with comparable salt levels at moderate and high salinity. A total of 20 commercial hybrid and 16 Canadian native willow genotypes were treated for 8 weeks in the first trial, of which a selection of 12 were further assessed for 12 weeks in the second trial. The genotypes were monitored for growth traits, and gas exchange during the trials. Elemental analyses of leaves and roots were performed via inductively coupled plasma mass spectrometry, and targeted metabolite profiling was used to quantify sugars, organic acids, amino acids, and glutathione in leaves by high performance liquid chromatography and spectrophotometry. Leaf samples of two genotypes, LAR-3, a sodium excluder, and MJW-2, a sodium accumulator, were selected for mRNA sequencing. Overall, it can be concluded that hybrid willows grew better at moderate salinity, while native willows are better suited for higher salinity conditions. Magnesium affected willows more significantly than sodium, largely inhibiting plant growth, mineral balance, photosynthesis, and primary metabolism. In addition, excess sulphate uptake and assimilation induced by sulphate salinity were witnessed. An assessment of growth, physiological, biochemical, and transcriptomic levels uncovered a more comprehensive view of salt responses, strategies, and defence mechanisms in willows.

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