© 2007 Heron Publishing—Victoria, Canada
Variation in drought resistance, drought acclimation and water conservation in four willow cultivars used for biomass production
Jenny Wikberg (1) and Erling Ögren (1, 2)
1. Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences,
SE-901 83 Umeå, Sweden / 2. Corresponding author (erling.ogren@genfys.slu.se) / Received October 29, 2006; accepted December 4, 2006; published online June 1, 2007
Summary
Growth and water-use parameters of four willow (Salix spp.) clones grown in a moderate drought regime or with ample water supply were determined to characterize their water-use
efficiency, drought resistance and capacity for drought acclimation. At the end of the 10-week, outdoor pot experiment, clonal
differences were observed in: (1) water-use efficiency of aboveground biomass production (WUE); (2) resistance to xylem cavitation;
and (3) stomatal conductance to leaf-specific, whole-plant hydraulic conductance ratio (gst/KP; an indicator of water balance). Across clones and regimes, WUE was positively correlated with the assimilation rate to stomatal
conductance ratio (A/gst), a measure of instantaneous water-use efficiency. Both of these water-use efficiency indicators were generally higher in
drought-treated trees compared with well-watered trees. However, the between-treatment differences in (shoot-based) WUE were
smaller than expected, considering the differences in A/gst for two of the clones, possibly because plants reallocated dry mass from shoots to roots when subject to drought. Higher
root hydraulic conductance to shoot hydraulic conductance ratios (KR/KS) during drought supports this hypothesis. The same clones were also the most sensitive to xylem cavitation and, accordingly,
showed the strongest reduction in gst/KP in response to drought. Drought acclimation was manifested in decreased gst, gst/KP, osmotic potential and leaf area to vessel internal cross-sectional area ratio, and increased KR, KP and WUE. Increased resistance to stem xylem cavitation in response to drought was observed in only one clone. It is concluded
that WUE and drought resistance traits are inter-linked and that both may be enhanced by selection and breeding.
Keywords:
cavitation, hydraulic conductance, osmotic potential, stomatal conductance, water-use efficiency.
