Explanations for the occurrence of deep-rooted plants in arid and semi-arid ecosystems have traditionally emphasized the uptake of relatively deep soil water. However, recent hydrologic data from arid systems show that soil water potentials at depth fluctuate little over long time periods, suggesting this water may be rarely utilized or replenished. In this study, we examine the distributions of root biomass, soil moisture and nutrient contents to 10-m depths at five semi-arid and arid sites across southwestern USA. We couple these depth distributions with strontium (Sr) isotope data that show deep (>1 m) nutrient uptake is prevalent at four of the five sites. At all of the sites, the highest abundance of one or more of the measured nutrients occurred deep within the soil profile, particularly for P, Ca2+ and Mg2+. Phosphate contents were greater at depth than in the top meter of soil at three of five sites. At Jornada, for example, the 2-3 m depth increment had twice the extractable P as the top meter of soil, despite the highest concentrations of P occurring at the surface. The prevalence of such deep resource pools, and our evidence for cation uptake from them, suggest nutrient uptake as a complementary explanation for the occurrence of deep-rooted plants in arid and semi-arid systems. We propose that hydraulic redistribution of shallow surface water to deep soil layers by roots may be the mechanism through which deep soil nutrients are mobilized and taken up by plants.
|Number of pages
|Published - Dec 2004
Bibliographical noteFunding Information:
Acknowledgements This research was supported by the USDA and by the Biological and Environmental Research (BER) Program, US Department of Energy, through the Southcentral Regional Center of NIGEC. Additional funding came from a NSF CAREER grant and the Andrew W. Mellon Foundation. W.H. Schlesinger, D. D. Richter, and two anonymous reviewers provided helpful suggestions on the work presented here.
- Cation uptake
- Deep roots
- Hydraulic redistribution
- Nutrient uplift
- Strontium isotopes
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics