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University of Arizona (1977)

THE PHYSIOLOGICAL BASIS FOR CALCICOLY OF LARREA DIVARICATA

Musick, Hugh Bradley

Titre : THE PHYSIOLOGICAL BASIS FOR CALCICOLY OF LARREA DIVARICATA

Auteur : Musick, Hugh Bradley

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1977

Résumé
The distribution of Larrea divaricata Cav. in relation to soil CaCOj was examined in a portion of the Walnut Gulch Exp c ’£ i merit 2.2. Watershed, near Tombstone in southeastern Arizona. Although moderately frequent on calcareous soils, :L. divaricata was extremely rare on soils with non-calcareous, slightly acid to circumneutral surface horizons. Some mechanisms that might account for the exclusion of L. divaricata from non-calcareous soils were investigated. Soil CO^ concentrations during the summer rainy season tended to be slightly higher in non-calcareous soils than in calcareous soils, but did not exceed 0.41%. In solution culture, 1% CO^ at pH 6, pH 7, or pH 8 had no significant effect on root length of seedlings seven days old. Root elongation during the first three days appeared to be inhibited by high HC03 concentrations, produced either by high pH or by high CO^ concentrations. Carbon dioxide toxicity cannot account for exclusion of L. divaricata from non-calcareous soils. Cotyledon necrosis and seedling mortality occurred after 1-2 wk in solution culture at pH 6, but not at pH 8. The nature of this pH effect in solution culture was investigated in order to predict the likelihood of such an effect in the field. Necrosis was apparently caused by toxic accumulations of P in the cotyledons. At pH 6, P concentrations as low as 10 yM in solution resulted in P toxicity, owing primarily to the extremely high P uptake rate, 52 ]imol (g fresh root wt) day \ Increasing pH to 8 decreased P uptake per unit root weight by 69-86%, and thus increased the solution P level necessary for toxicity. Slow growth and an ample supply of P from the seed con tributed to early development of P toxicity when uptake rates were high and also enabled seedlings with no external supply to avoid P de ficiency for 3-4 wk after germination.

Mots clés : Larrea divaricata. ; Plants — Effect of soil acidity on.

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