Fine-scale mapping of sapwood anatomical properties reveals plasticity in hydraulics during water deficit

Growth responses to water deficit translate into discernible changes in the structure of woody tissues and provide an integrated record of historical water availability throughout the life of the individual. The highly dynamic nature of woody growth can impart adaptive changes in physiological performance through changes in xylem elements that regulate water transport. Here, we present a case study of how sapwood anatomical properties can be mapped using point dendrometers, in a diffuse porous, Eucalyptus spp. to reveal plasticity in hydraulic architecture under water deficit. Reductions in stem growth in response to water deficit coincided with marked changes sapwood vessel anatomy that could be matched to the commencement of large fluctuations in stem radius. These changes included: a reduction in hydraulically-weighted vessel diameter, increases in vessel density, sapwood lumen fraction and density and increase in wall strength. However, no changes in estimated stem conductivity were observed during the water deficit. This approach emphasises the responsiveness of species such as Eucalyptus to changes in water supply and provides an illustration of how we might detect short-term and rapid changes in stem hydraulic architecture in response to water availability and other environmental controls.