Relationships Between Water Availability and Selected Vessel Characteristics in Eucalyptus Grandis and Two Hybrids
The primary objective of this study was to determine the relationships between water availability, plant growth and selected vessel characteristics for Eucalyptus grandis and two hybrids, so as to ascertain whether these xylem characteristics predict water use efficiency. Cuttings of Eucalyptus grandis, E. grandis × camaldulensis and E. grandis × nitens were planted in 220 litre drums from which rainfall was excluded. One half of the individuals received a low watering treatment; one half received a higher watering treatment. Soil moisture depletion through root uptake was monitored weekly and the removed water replaced to maintain 60 and 80 litres in the pots of the low and high watering treatments respectively. Mean values for tangential vessel diameter, vessel frequency and vessel element length were compared for the two treatments. In E. grandis and the hybrid E. grandis × camaldulensis vessel diameter (P < 0.01 ' P < 0.05 respectively) and vessel element length (P < 0.05 for both) increased from the dry to the wet treatment as water uptake through transpiration increased. There is no significant correlation between available water and vessel frequency. For E. grandis × nitens, on the other hand, only vessel frequency was significantly (P < 0.01) correlated with water uptake. In all three species/hybrids water availability also had a significant influence on stem diameter (P < 0.0001) and transverse sectional stem area (P < 0.0001) which increased with increased water consumption. These results suggest that E. grandis × nitens may be more water use efficient than E. grandis, which is commonly grown for timber and thus could potentially be used as a replacement species that is more water conservative in this water limited region.