Phosphorous and pH tolerances in the germination of the desert shrub <i>Larrea tridentata</i> (Zygophyllaceae)

Seeds of <i>Larrea tridentata</i>, a dominant shrub of deserts in the southwestern U.S., were germinated on both a pH and phosphorus (P) gradient to determine if requirements for germination can help explain the field distribution of <i>Larrea</i>. Germination decreased significantly above pH 8, which is consistent with the conspicuous absence of <i>Larrea</i> from high pH sodic or saline desert soils. Although <i>Larrea</i> tends to be absent from noncalcareous soil, seed germination was not inhibited in acidic solutions. Germination showed no response to P or to interactions of pH and P. In contrast, recent literature has suggested that <i>Larrea</i> may be restricted to calcareous soils of low phosphorus availability due to toxicity of high concentrations of P to seedlings.