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Soil matric potential (psi(matric)) was modeled for two years at four sites with different soil profile characteristics. Canopy volumes and foliar N-15 ratios (delta N-15) of Larrea tridentate were related to average soil water availability (psi(matric)) and the modeled duration of available soil water (Consecutive days psi(matric) > -6.0 MPa). Weakly developed soils on young (Holocene) alluvial deposits had the longest duration (129 d) and highest psi(matric) (-1.8 MPa), compared to soils with moderate horizon development in intermediate-aged (late Pleistocene) deposits (80 d, -4.3 MPa) and in soils with strong horizons on old (mid-late Pleistocene) deposits (20 d, -3.2 MPa). Plant canopy volume was highest in weakly developed soils (2.23 m3 0.342 SE) than in moderately or strongly developed older soils (0.57 m(3) +/- 0.082 SE; 0.56 m(3) +/- 0.123 SE, respectively). The fourth site possessed a soil with a silt- and clay-rich horizon beneath a strong stone pavement, and had the shortest, most water-limited regime (13 d; -5.5 MPa) and smallest plant canopies (0.46 m(3) +/- 0.073 SE). Foliar delta N-15 variation was better explained by average psi(matric) (R-2 = 0.69; p <= 0.001) than duration of available soil water (R-2 = 0.49; p <= 0.001). Together, these findings suggest soil hydrological regimes establish thresholds for plant growth, and plant N-dynamics are tightly coupled to desert soil hydrological characteristics. Published by Elsevier Ltd.