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Title: Effect of Phosphorus Deficiency and High Temperature on Ammonium and Nitrate Uptake by Geranium (Pelargonium x hortorum Bailey)

Author
item TAYLOR, MATTHEW - NORTH CAROLINA STATE UNIV
item NELSON, PAUL - NORTH CAROLINA STATE UNIV
item Frantz, Jonathan
item RUFTY, THOMAS - NORTH CAROLINA STATE UNIV

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 3/14/2007
Publication Date: 7/14/2007
Citation: Taylor, M., Nelson, P., Frantz, J., Rufty, T. 2007. Effect of Phosphorus Deficiency and High Temperature on Ammonium and Nitrate Uptake by Geranium (Pelargonium x hortorum Bailey). HortScience Annual Meeting July 16-19, 2007, Scottsdale, AS. 42:890.

Interpretive Summary:

Technical Abstract: The cause of sudden substrate pH decline by geranium is unknown and may be due to a shift in cation-anion balance. Nitrogen plays a very important role in cation-anion balance since it accounts for over 50% of the mineral ions that will cross the plasma membrane and is the only mineral nutrient that can be absorbed as a cation (NH4+) or anion (NO3-). Studies have shown that P deficiency will suppress NO3- uptake or suppress NO3- uptake and increase NH4+ uptake. These changes cause a shift in the cation-anion uptake ratio and if favored towards NH4+ would cause acidification of the rhizosphere. This experiment compared geraniums (Pelargonium x hortorum Bailey ‘Designer Dark Red’) grown in 200 L hydroponic tanks at 2 temperatures (18/22 and 22/26° C night/day) and with or without P. 3, 11, and 19 days after transplanting (DAT), plants were placed into an identical solution contain either 15NH4+ or 15NO3- for 24 hours. Influx of 15NH4+ was not significantly affected by temperature and was suppressed by P starvation 19 DAT. Influx of 15NO3- was not significantly affected by temperature and was suppressed by P starvation 11 and 19 DAT. At the control temperature treatment the 15NH4+:15NO3- influx ratio increased significantly from 0.34 to 0.46 and 0.30 to 0.38 when plants did not receive P at 11 and 19 DAT, respectively. This suggests an increased acidification rate by P starved plants. pH was maintained at 5.8 throughout the experiment and tanks with plants receiving P consumed less than half the mEq of titrating base per gram dry weight plant than tanks with plants that were devoid of P. Data indicate P stressed geraniums suppress uptake of N (primarily NO3-) and increase the rate of acidification, which offers one explanation for sudden substrate pH decline.