Do arid species use less water than mesic species in an irrigated common garden?

There is an increasing need to consider the water use of horticultural plants grown in arid and semi-arid garden settings. Species that originate from arid and semi-arid regions are often considered suitable for xeriscaping, but there have been relatively few direct measurements of important water relations parameters such as gas exchange, resistance to cavitation, and water use efficiency (WUE) in irrigated urban gardens. In this study, we compared plant gas exchange, cavitation resistance, and WUE in evergreen shrub species from arid, temperate, and tropical environments grown in an irrigated common garden environment. Contrary to expectations, arid and non-riparian species had greater transpiration rates than temperate and riparian species, and lower specific leaf area than tropical and riparian species. Temperate species had the highest WUE as measured with the isotopic composition of leaf soluble sugar. Cavitation resistance and maximum hydraulic conductivity were not different among species from different biomes. These results indicate that under well-watered conditions, species from temperate environments may use less water than species from arid environments. In addition, native habitat is not a strong predictor of resistance to cavitation, which has implications for plant responses to water stress and drought.