Water relations and leaf chemistry of <i>Chrysothamnus nauseosus</i> ssp. <i>consimilis</i> (Asteraceae) and <i>Sarcobatus vermiculatus</i> (Chenopodiaceae)

Abstract

At Mono Lake, California, we investigated field water relations, leaf and xylem chemistry, and gas exchange for two shrub species that commonly co‐occur on marginally saline soils, and have similar life histories and rooting patterns. Both species had highest root length densities close to the surface and have large tap roots that probably reach ground water at 3.4‐5.0 m on the study site. The species differed greatly in leaf water relations and leaf chemistry. Sarcobatus vermiculatus had a seasonal minimum predawn xylem pressure potential (ψ pd ) of ‐2.7 MPa and a midday potential (ψ md ) of ‐4.1 MPa. These were significantly lower than for Chrysothamnus nauseosus , which had a minimum ψ pd of ‐1.0 MPa and ψ md of ‐2.2 MPa. Sarcobatus had leaf Na of up to 9.1 % and K up to 2.7 % of dry mass, and these were significantly higher than for Chrysothamnus which had seasonal maxima of 0.4% leaf Na and 2.4 % leaf K. The molar ratios of leaf K/Na, Ca/Na, and Mg/Na were substantially lower for Sarcobatus than for Chrysothamnus. Xylem ionic contents indicated that both species excluded some Na at the root, but that Chrysothamnus was excluding much more than Sarcobatus. The higher Na content of Sarcobatus leaves was associated with greater leaf succulence, lower calculated osmotic potential, and lower xylem pressure potentials. Despite large differences in water relations and leaf chemistry, these species maintained similar diurnal patterns and rates of photosynthesis and stomatal conductance to water vapor diffusion. Sarcobatus ψ pd may not reflect soil moisture availability due to root osmotic and hydraulic properties.