© 2004 Heron Publishing—Victoria, Canada
Wood density and anatomy of water-limited eucalypts
Matthew J. Searson (1, 2), Dane S. Thomas (3), Kelvin D. Montagu (4) and Jann P. Conroy (1)
1. Centre for Horticulture and Plant Sciences, University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia / 2. Corresponding author (m.searson@uws.edu.au) / 3. State Forests of NSW, Research and Development Division, P.O. Box J19, Coffs Harbour Jetty, NSW 2450, Australia / 4. State Forests of NSW, Research and Development Division, P.O. Box 100, Beecroft, NSW 2119, Australia / Received December 22, 2003; accepted April 18, 2004; published online September 1, 2004
Summary
We hypothesized that seedlings grown under water-limited conditions would develop denser wood than seedlings grown under well-watered
conditions. Three Eucalyptus species (E. grandis Hill (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis Endl.) were grown in a temperature-controlled greenhouse for 19 weeks with watering treatments (well-watered and water-limited)
applied at six weeks. The water-limitation treatment consisted of four drought cycles. Wood density increased by between 4
and 13% in the water-limited seedlings, but this increase was mainly due to extractive compounds embedded in the cell wall
matrix. Once these compounds were removed, the increase was 0–9% and was significant for E. grandis only. Water-limitation significantly reduced mean vessel lumen area; however, this was balanced by a trend toward greater
vessel frequency in water-limited plants, and consequently there was no difference in the proportion of stem area allocated
to vessels. Conduit efficiency value was lowest in the water-limited plants, indicating that there was a cost in terms of
stem hydraulic conductivity for decreasing vessel lumen area. Wood density was negatively correlated with vessel lumen fraction
in well-watered plants, but this relationship broke down in the water-limited plants, possibly because of the significantly
larger proportion of the stem taken up by pith in water-limited seedlings. Diurnal variation in leaf water potential was positively
correlated with wood density in well-watered plants. This relationship did not hold in the water-limited plants owing to the
collapse of the pressure gradient between soil and leaf. We conclude that drought periods of greater than 1 month are required
to increase wood density in these species and that increases in wood density appear to result in diminished capacity to supply
water to leaves.
Keywords:
conduit efficiency, extractives, pith, vessels, water stress.
