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Phosphorus deficiency in Pelargonium: effects on nitrate and ammonium uptake and acidity generation

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A sudden pH decline (SPD) of the substrate is an increasing problem in geranium growth systems, and the cause is unknown. In this study, we investigate whether a phosphorus (P) deficiency can cause SPD, and whether the effect is related to inhibition of ammonium (NH4+) and nitrate (NO3-) uptake and a corresponding shift in the cation to anion uptake balance. Geraniums (Pelargonium x hortorum Bailey 'Designer Dark Red') were grown in hydroponic solutions with or without P, and the hydroponics systems were located in a growth chamber programmed for light/dark temperatures of 22/18 or 26/22°C. Acidification potential was measured by the amount of base required to maintain pH at 5.8. The results indicated that much greater amounts of base were required to maintain a stable pH with P-limited plants. Using periodic exposures to 15NH4+ or 15NO3-, it was found that NO3- uptake was strongly inhibited as plants became P stressed. Tissue nutrient profiles showed that the NO3- uptake inhibition was accompanied by an increase in the cation to anion uptake ratio. Rhizosphere acidification was greater at higher temperature even though the cation and anion responses were unchanged in control plants, suggesting the involvement of carbon dioxide (CO2) generated by root respiration. The results indicate that changes in cation and anion uptake and the associated increase in net H+ extrusion that occur under P-stress conditions can contribute to SPD in geranium culture systems.
Taylor, Matthew D. , Nelson, Paul V. , Frantz, Jonathan M. , Rufty, Thomas W.
Includes references
Journal of plant nutrition 2010, v. 33, no. 5-8
Journal Articles, USDA Authors, Peer-Reviewed
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