Response of four Salix species to soil water deficit

Growth and water-use efficiency were measured over twelve weeks in potted cuttings of two tree willow species, Salix matsudana x alba 'Tangoio' and S. lucida spp lasiandra, and two shrub willow species, S. schwerinii 'Kinuyanagi' and S. lasiolepis grown in a glasshouse under three soil water regimes: well watered (WW), moderate deficit (MD) and severe deficit (SD). The shrub willows are possible alternatives to the tree willows for use in riverbank stabilisation in regions where willow sawfly Nematus oligospilus has defoliated and killed tree willows, and may be preferable for industrial applications requiring efficiency in removing water and nitrogen from soil. Dry mass accumulation was greatest in Salix matsudana x alba 'Tangoio' and lowest in S. lasiolepis in WW treatment, but differences were less in the MD and SD treatments. Whole-plant water-use efficiency (W-p), measured as dry mass accumulation divided by plant water-use, was not significantly different between MD and WW treatments. Mean dry weight gain was negative in all plants surviving the SD treatment. Carbon allocation to root growth was lowest in S. schwerinii 'Kinuyanagi' which may account for its inability to survive the SD treatment. Carbon allocation to leaf growth was significantly higher in the shrub species and allocation to stem growth was correspondingly lower.