Some trees might have adapted to cope with embolisms instead of preventing them

Lone Juniper in a Drought
Lone Juniper, Canyon Overlook, Zion 5-14. Photo: Don Graham / Flickr.

Drought is expected to increase in frequency and duration throughout the 21st century. However, it remains unclear how vegetation will respond to drought because the underlying physiological mechanisms are not well understood. During drought, hydraulic dysfunction may occur due to the formation of embolism or a gas-filled bubble that blocks the water transport pathway.

It is hypothesized that embolism can be repaired (i.e. refilled or reversed) using water stored in stem sapwood. This stored water, measured as capacitance, is thought to be driven into embolized vessels via osmotic mechanisms or aquaporins, thus refilling the xylem.

Trifilò et al. (2015) investigated how stem sapwood capacitance (i.e. water storage) that should confer enhanced embolism repair capacity relates to vulnerability to embolism. They found that species that were more vulnerable to embolism had wood traits that should allow for embolism reversal, such as high capacitance and low wood density.

Past research has used species-specific vulnerability to embolism to infer plant survival and mortality. However, Trifilò et al. (2015) show that this metric does not necessarily predict survival to water stress, because species may compensate for a high vulnerability to embolism with more efficient embolism repair.

Trifilò P, Nardini A, Lo Gullo MA, Barbera PM, Savi T, Raimondo F. 2015. Diurnal changes in embolism rate in nine dry forest trees: relationships with species-specific xylem vulnerability, hydraulic strategy and wood traits. Tree Physiology. http://dx.doi.org/10.1093/treephys/tpv049