Water relations of riparian plants from warm desert regions

Abstract

Riparian plants have been classified as "drought avoiders" due to their access to an abundant subsurface water supply. Recent water-relations research that tracks water sources of riparian plants using the stable isolopes of water suggests that many plants of the riparian zone use ground water rather than stream water, and not all riparian plants are obligate phrcatophytes (dependent on ground water as a moisture source) but may occasionally be dependent on unsaturated soil moisture sources. A more thorough understanding of riparian plant-water relations must include water-source dynamics and how lhose dynamics vary over both space and time. Many rivers in the desert Southwest have been invaded by the exotic shrub Tamarix ramosissima (saltcedar). Our studies of Tamarix invasion into habitats formerly dominated by native riparian forests of primarily Populus and Salix have shown that Tamarix .~ucccssfully invades these habitats because of its (1) greater tolerance to water stress and salinity, (2) status as a facultative, rather than obligate, phreatophyte and, therefore, its ability to recover from droughts and periods of ground-water drawdown, and (3) superior regrowth after fire. Analysis of wate~loss rates indicate that Tamarix-dominated stands can have extremely high evapetranspiration rates when water tables are high but not necessarily when water tables are lower. Tamarix has leaf-level transpiration rates that are comparable to native species, whereas sap-flow rates per unit sapwood area are higher than in natives, suggesting that Tamarix maintains higher leaf area than can natives, probably due to its greater water stress tolerance. Tarnarix desiccates and salinizes floodplains, duc to its salt exudation and high transpiration rates, and may also accelerate fire cycles, thus pre disposing these ecosystems to further loss of native taxa. Riparian species on regulated rivers can be exposed to seasonal water stress due to depression of floodplain water tables and elimination of annual floods. This can potentially result in a community shift toward more stress-tolerant taxa, such as Tamarix, due to the inability of other riparian species to germinate and establish in the desiccated floodplain environment. Management eflbrts aimed at maintaining native forests on regulated rivers and slowing the spread of Tamarix inva.~ion must include at least partial reintroduction of historical flow regimes, which favor the recruitment of native riparian species and reverse tong-term desiccation of desert floodplain environments.

Water uptake from different soil depths for halophytic shrubs grown in Northern area of Ningxia plain (China) in contrasted water regimes

“…According to the extent of this dependence, phreatophytes are classified as either 'obligate' (plants that utilize only shallow alluvial groundwater) or 'facultative' (plants that have the ability to utilize sources in addition to alluvial groundwater) (Busch et al 1992;Horton et al 2003). T. ramosissima has been listed as facultative phreatophytes, it utilizes only groundwater when this water source is shallow and relatively constant in depth, but is also able to extract water from unsaturated soil by its greater root allocation and physiological adaptability to a higher degree of water stress when groundwater is deeper and temporally more variable in depth (Busch et al 1992;Busch & Smith 1995;Horton et al 2001;Smith et al 1998). However, the controversial documents are not scarce.…”

A Review of Advances in the Identification and Characterization of Groundwater Dependent Ecosystems Using Geospatial Technologies

“…Stable isotope composition of water in the branches of trees is considered to be useful in determining if a given plant is accessing groundwater [56,57]. Moreover, comparison between the stable isotope composition of soil water, surface water, xylem water, and groundwater can confirm the vegetation reliance on the groundwater resource [58][59][60], particularly in semi-arid regions in which groundwater originated from snowmelt or winter precipitation and therefore has a distinctive isotopic composition [61]. Stable water isotopes have been used in a variety of studies and applications related to GDEs: to examine springs in the boreal regions [62], to examine the water uptake patterns in woody riparian GDEs of the southwestern United States [63], and to determine the seasonal water sources of woody GDEs and their connection to soil water content [64].…”

Effect of soil salinity and nutrient levels on the community structure of the root-associated bacteria of the facultative halophyte, <i>Tamarix ramosissima</i>, in southwestern United States

“…Currently, T. ramosissima is widely distributed along major river systems and reservoirs in Arizona, Colorado, Kansas, Nevada, New Mexico, Southern Effect of soil salinity and nutrient levels on the community structure of the root-associated bacteria of the facultative halophyte, Tamarix ramosissima, in southwestern United States (Received January 24, 2015;Accepted July 26, 2015) Takeshi Taniguchi (Shafroth et al, 2010). The extent of T. ramosissima invasion causes problems of excessive water consumption and the disturbance of native ecosystems, particularly in arid and semiarid regions (Horton et al, 2001;Shafroth et al, 2005;Smith et al, 1998). T. ramosissima is a facultative halophyte that survives in a broad range of environmental salt levels (Ohrtman and Lair, 2013), in which native riparian trees, such as cottonwood and willow, have difficulty thriving (Nagler and Glenn, 2013).…”