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. 2007. Effect of High Temperature on Extreme Substrate Acidification by Geranium (Pelargonium x hortorum Bailey). American Society for Horticultural Science, July 16-19, 2007, Scottsdale, AZ. 42:874. Interpretive Summary:
Technical Abstract: The cause of sudden substrate pH decline by geranium is unknown and previous reports suggest it may be due to high temperature. The first of 2 experiments compared plants grown at 4 temperatures (14/10, 18/14, 22/18 and 26/22º C day/night). With increasing increments of temperature, substrate pH declined from 6.8 to 4.6 at 63 d. Low tissue P has also been shown to cause plants to acidify. In the first experiment, tissue P was deficient (below 0.2) in the 3 highest temp treatments and it was unclear whether the cause of substrate acidification was due to P deficiency and/or high temperature. The second experiment was a factorial of 3 temperatures (18/14, 22/18 and 26/22º C day/night) by 5 pre-plant P rates [0, 0.33, 0.67, 1.33, 2.67 g triple superphosphate (TSP) • L-1 substrate]. At 28 d tissue P was adequate in plants at all temperature and P treatments except 0 TSP. Yet, pH was lower in the high temperature treat with all P rates except the highest, indicating that temperature acts independent of tissue P level. At 63 d in the 0.33 and 0.67 TSP treatment, tissue P was deficient but not significantly different and pH decreased with increasing temperature from 5.6 to 4.8 and 5.9 to 4.7, respectively. At the 1.33 TSP treatment tissue P is adequate at low temperature and deficient at the two higher temperatures yet pH decrease as temperature increase. In the highest P treatment all tissue P levels are adequate and pH declines with each increase in temperature. Again, the 63 day results show that temperature is acting independent of tissue P. When plants received P, pH fell to below 5.2 by 57 d when temperature was high. These data indicate high temperature stressed geraniums increase the rate of acidification, which offers one explanation for sudden substrate pH decline.