Most studies of hydraulic architecture have focused on inter-specific comparisons of measurements made on small diameter roots and stems. These cross-species studies often do not observe higher hydraulic conductivity at the cost of greater xylem vulnerability to embolism, despite this tradeoff frequently being predicted. We hypothesized that this tradeoff would be much more evident in intra-specific comparisons along the hydraulic pathway from roots to leaves. To test this, we measured xylem vulnerability to embolism and specific conductivity in a variety of organs in a number of conifer species in the Pacific Northwest. Vulnerability curves were constructed using acoustic emissions and pressure sleeve methods, and conductivity was measured gravimetrically or with a high pressure flow meter
Results/Conclusions
We found that the tradeoff between hydraulic conductivity and xylem vulnerability to embolism is much stronger when examined intra-specifically versus inter-specifically. Within a species, an increase in specific hydraulic conductivity was associated with a decline in resistance to embolism. The lack of an inter-specific tradeoff may be because different species have evolved diverse solutions to the safety versus efficiency tradeoff. Along the hydraulic continuum within individuals from the same species, though, there does not seem to be a way to simultaneously maximize the two parameters. This tradeoff has implications for species distributions, maximum height and, perhaps, growth form.
