Xylem potential- and water content-breakpoints in two wetland forbs: indicators of drought resistance in emergent hydrophytes

BW Touchette, AR Frank
2009 Aquatic Biology  
Freshwater wetlands commonly occur along the boundaries between terrestrial upland and deep open-water systems, and are consequently prone to dynamic and often highly variable hydrological regimes. Physiological adaptations to drought would be advantageous in emergent vegetation, as wetlands are often susceptible to short periods of water scarcity through seasonal declines in precipitation and/or surface water runoff. This study used 15 l microcosms to examine xylem water potential (ψ xylem
more » ... ential (ψ xylem )-and tissue water content (θ)-breakpoints in 2 wetland forbs (Justicia americana and Saururus cernuus) to determine how these plants respond to short-term (2 wk) water deficits. Overall, treatment responses by these forbs included reductions in both θ and ψ xylem during the second week of drought, followed by rapid recoveries of θ and ψ xylem within a few days of water repletion. Rapid tissue-water recovery, following extreme water deficits (soil moisture levels < 3%), is beneficial to plants residing in areas prone to intense water fluctuations. Furthermore, while θ and ψ xylem breakpoints in S. cernuus occurred as soil moisture levels fell below 12% (ca. -800 kPa soil water potential), breakpoints for J. americana occurred at considerably lower soil moisture levels (ca. 7 and 10% soil water content for θ and ψ xylem , respectively; or less than -1500 kPa soil water potential). The lower breakpoints observed in J. americana were comparable to values reported for terrestrial grasses, including species adapted to dryer, xeric conditions. Therefore, the results from this study suggest that some wetland forbs are physiologically adapted to environments that undergo rapid changes in water hydrology, including the ability to tolerate short-term water scarcity comparable to dryer upland systems. KEY WORDS: Wetlands · Drought · Water potential · Xylem breakpoint · Plant -water relations Resale or republication not permitted without written consent of the publisher OPEN PEN
doi:10.3354/ab00168 fatcat:5td74c5d25f3ll2xmsysm6flv4