Screening for salinity tolerance: linking physiological processes with growth constraints in willows

1 Raju Soolanayakanahally, Agriculture and Agri-Food Canada

2 Hamid Naeem, Agriculture and Agri-Food Canada

3 Craig Gatzke, Agriculture and Agri-Food Canada

4 Ken Wall, Agriculture and Agri-Food Canada

5 Robert D. Guy, University of British Columbia

Salinity is one of the major abiotic stress affecting plant growth and biomass productivity. An estimated four million hectares of salt-affected land exists on Canadian prairies. These agriculturally marginal lands offer huge potential to grow bioenergy feedstock such as, poplars and willows. By making use of a subset of much larger AgCanSalix collection, a mix of native (n=16) and hybrid (n=20) willow cuttings were rooted in hydroponically-nourished sand pots featuring automatic control over irrigation, fertility and root-zone salinity at AAFC's Salinity Lab, Swift Current. Four weeks after plant establishment, the willow roots were exposed to three levels of salt (control - 1.5 dS/m; moderate - 7.0 dS/m; severe - 14.0 dS/m) for a period of six weeks. Later, we studied the effects of prolonged salinity on willow growth, photosynthetic rates (A), carbon isotope discrimination (δ13C), chlorophyll content index (CCI) and chlorophyll fluorescence (Fv/Fm). In addition, leaf and root Na+ and K+ concentrations were analyzed. Under severe salinity striking differences exists in salt tolerance - (i) native willows displayed higher A (8.24 μmol CO2 m-2 s-1 vs. 0.77 μmol CO2 m-2 s-1), height gain (103 cm vs. 37 cm) and CCI (32.5 vs. 13.5) than hybrids; (ii) native willows also maintain higher K+/Na+ ratio (36 vs. 2.04) and greater water use-efficiency (17.49‰ vs. 13.50‰) compared to hybrids; (iii) above-ground stem dry weight was bigger among natives (2.92 g vs. 1.69 g). Overall, willow genotypes identified with enhanced salt tolerance provide opportunities for agroforestry on marginal lands and reclamation applications.