Depth of water acquisition by invading shrubs and resident herbs in a Sierra Nevada meadow

Abstract

Woody plant encroachment into semiarid ecosystems has become a global trend in recent decades. Due to stream channel incision, the semiarid riparian montane meadows of the southern Sierra Nevada Mountains, USA are experiencing long-term declines in soil moisture. A woody shrub, Artemisia rothrockii A. Gray (Rothrock sagebrush, Asteraceae) is invading these herbaceous meadows. We used an analysis of the stable oxygen isotope ratios of plant and soil water to measure the depth of plant water acquisition during the early stages of this woody plant encroachment. Sagebrush used deeper water on average than most herbs, but it also acquired 10-30% of its water from shallow (<30 cm) soil. Most of the young sagebrush seedlings (1-3 years old, <15 cm) that we sampled used deep water like the older shrubs. Many, but not all of the herb species we sampled were also able to acquire deep water. These findings are consistent with a scenario of shrub encroachment in which channel incision causes shallow-water-dependent herbs to die back, allowing shrub seedlings to establish in disturbed areas during wet years. At least during the early stages of the invasion, some herbs appear to coexist with sagebrush by using deep root systems to cope with the declining shallow soil moisture.

Using stable isotopes to determine seasonal variations in water uptake of summer maize under different fertilization treatments

“…Therefore, comparison of the isotopic composition in the plants and possible sources of water can be used to infer the depth of water uptake (Brunel et al, 1995). The proportion of varying potential water sources accessed by plants was preliminarily determined using stable isotope analysis in conjunction with two-or three-compartment linear mixing models (Snyder and Williams, 2000;Darrouzet-Nardi et al, 2006;McCole and Stern, 2007). However, the linear mixing models were unable to provide a unique solution when the number of sources exceeded three.…”

Rare drought-induced mortality of juniper is enhanced by edaphic stressors and influenced by stand density

“…Although junipers may invest heavily in near-surface roots (Breshears et al, 1997), they also typically invest in deeper taproots (Johnsen, 1962) which may allow access to deeper water sources than herbaceous vegetation can exploit, reducing the importance of competitive pressure from herbs (Darrouzet-Nardi et al, 2006). The spacing of trees was quite influential, apparently in a competitive manner in grasslands and a facilitative manner in woodlands.…”

Montane meadows in the Sierra Nevada: comparing terrestrial and aquatic assessment methods

“…It is not clear how many of our sites have shifted meadow type due to slight changes in the water table, given a general lack of historical data. Moderate drops in the water table due to a minor amount of stream down-cutting can result in subtle shifts in vegetation communities, particularly at the meadow upland/meadow ecotone, farthest from the water table and stream, which would not be reflected in the index, especially as we used it (Chambers et al 2004;Darrouzet-Nardi et al 2006;Dwire et al 2006).…”