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

Abstract

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 )-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.

Growth and water relations in a central North Carolina population of Microstegium vimineum (Trin.) A. Camus

“…5). This lower breakpoint is consistent with plants that are Growth and water relations in a central North Carolina population 899 more tolerant to low water conditions (Milnes et al 1998;Romanello et al 2008;Touchette and Frank 2009). Along with its ability to sustain comparatively high tissue water potential and water content with diminishing soil moisture, maintaining comparatively rigid cell walls (i.e., higher e) can also confer some advantages during drought conditions.…”

“…), water content breakpoints were observed between 6 and 9% soil moisture (Milnes et al 1998). In contrast, breakpoints for aquatic plants often fell between 10 and 15% soil moisture (Romanello et al 2008;Touchette and Frank 2009). While it is difficult to determine water content breakpoints in M. vimineum from the data gathered in this study, it is apparent that the water potential breakpoint does fall below 10% soil moisture for this plant (Fig.…”

Laboratory study of subtropical wetland plant Lepironia articulata’s water use and sensitivity to groundwater availability

“…Only a few studies focus upon wetland vegetation response to constant drought conditions Touchette & Frank, 2009); however, the drying condition in these experiments was changed by terminating irrigation and did not consider groundwater drawdown. There are several studies that have looked at the impact of constant water drawdown on riparian vegetation (Amlin & Rood, 2002;Imada et al, 2010).…”