April 19 2011

12:00 BSRB 154

Ecolunch: Jochen Schenk

A Hard Day's Night: Nocturnal Removal of Air from Plant Hydraulic Systems


Two enduring mysteries of plant physiology are the function of nighttime transpiration and the nature of the mechanism that allows removal of air bubbles (embolisms) from a plant’s hydraulic system while the system is functioning under negative pressure. Nighttime transpiration is particularly common in plants from dry environments, which would appear to be least able to afford wasteful water loss. Refilling of air-filled conduits while the remaining hydraulic system is under negative pressure has been thought to be physically impossible, yet is commonly observed. In our lab, 10 out of 20 shrub species studied at field sites across the North American continent showed embolism repair under tension. All of these 10 species were from dry environments, and embolism repair occurred while stomata were at least partially open. Using the North American desert shrub Encelia farinosa (Asteraceae) as a focal study species, we found that experimental inhibition of nighttime transpiration by bagging of leaves inhibited embolism repair. Measurements of air flow into artificially created embolisms in the wood revealed that air from these embolisms dissolved into the transpiration stream of functioning conduits. Nighttime transpiration appears to be required to move air-saturated sap towards the leaves before temperatures increase again during the next morning, which would cause gas solubility to decrease and air to come out of solution. Nighttime transpiration, an important flux in the water balance of many ecosystems, is explained at least in part as playing a vital role in the nocturnal recovery from drought-stress experienced during the day.















































































































































































































































































































































































































































































































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