- This study evaluated biomass production, water-use efficiency (WUE), biomass allocation, and water use characteristics of common plant species in Owens Valley, California, USA. The species studied were the grasses Distichlis spicata, Leymus triticoides, and Sporobolus airoides, the forbs Glycyrrhiza lepidota, Juncus arcticus, and Salsola tragus (annual), the desert shrubs Artemisia tridentata, Atriplex confertifolia, and Ericameria nauseosa, and the riparian shrub Salix exigua. Plants of each species were established and grown in 2.4 m X 2.4 m plots in a common garden since 2005. Our first experiment was conducted in 2009 and 2010 and included four monthly summer water treatments: control (no additional water), low (1.3 cm), medium (2.6 cm) and high (3.9 cm). Biomass production and WUE (the amount of water that a plant uses to produce a unit of biomass) were lower in 2009 than in 2010. Water-use efficiency of grasses increased with increasing water application in 2009 but decreased with increasing water application in 2010. The difference between years was attributed to the difference in timing of natural precipitation with higher spring precipitation in 2010. Biomass production and WUE of desert shrubs were not significantly affected by water treatments. Water-use efficiency varied by species; some desert shrubs and the annual S. tragus were 13 times more efficient than the
riparian S. exigua. Total standing crop and root-to-shoot ratio (RSR) varied by species, but not by watering treatments. Although in general desert shrubs had higher standing crop than herbaceous species, the grass S. airoides had the highest standing crop overall. Graminoids had much higher RSR (3 to 6) than the shrubs did (< 1).
Our second experiment was conducted in 2010 using the experimental setting of the first experiment with the objective of determining soil water use and depth of soil water extraction by species. Three monthly watering treatments were applied during the summer months: low (1.3 cm), medium (2.6 cm), and high (3.9 cm). Plant water use was determined by calculating soil water depletion during irrigation cycles using time domain reflectometry (TDR) at two depths (0 - 25 cm and 0 - 50 cm) in vegetated plots. Evaporation was also obtained by water depletion on bare ground plots and subtracted from evapotranspiration to calculate water use. Water use varied by species; those with shallow, fibrous, and rhizomatous root systems such as J. arcticus and L. triticoides had higher water use than shrubs, including the riparian S. exigua. The ratio of deep water (25 - 50 cm) to shallow water (0 - 25 cm) use was 19 to 21 in desert shrubs and 1 to 2 in herbaceous species, indicating that shrubs may be more dependent on groundwater that shallow-rooted species such as grasses. In general, we observed large variability in biomass production, water-use efficiency, biomass allocation, and water-use characteristics among the typical plants of the Owens Valley, which should be considered in land and water management decisions. A potential increase in summer precipitation in the area might favor higher water utilization and higher production of shallow-rooted, high RSR plants such as grasses in detriment of desert shrubs.