Mycorrhizae, Water Relations, Growth, and Nutrient Uptake of Geranium Grown under Moderately High Phosphorus Regimes

by Michael R. Sweatt and Fred T. Davies, Jr.

To determine the role of endomycorrhizae on water relations and plant growth of geraniums under nonrate limiting soil P conditions, hybrid seedlings (Pelargonium Xhortorum Bailey cv. Cherry Glow) were planted in moderately high P (40 ppm) media, grown under high (-0.4 Mpa) or low (-1Mpa) soil water potential ( ), and either inoculated with VA mycorrhizal fungi [ Glomus mosseae (Nicol & Gerd) and G. faxcicualtus (Thaxt. Sensu Gerde.) Gerd. & Trappe] (VAM) or left as noninoculated controls. Geraniums grown under high moisture had greater shoot growth, more advanced floral development, and higher P uptake than the low moisture plants. Mycorrhizal plants under high moisture conditions had higher P levels than noninoculated plants, while mycorrhizal plants under low moisture regimes had greater shoot growth , more advanced floral formation, and greater N uptake than noninoculated plants. Xylem water potential in leaves ( ) was lower under 1 Mpa than 0.4 Mpa moisture regimes and lowest in mycorrhizal geraniums grown under 1Mpa . One hundred minutes after plants had recovered from water stress, the greatest change in was recorded for mycorrhizal-dependent. Total estimated root length and root water conductivity were lower with mycorrhizal geraniums under high water and P regime. Under water stress, the larger mycorrhizal geraniums have greater total water demands than controls. Consequently, mycorrhizal geraniums stressed more rapidly yet more efficiently recovered from water deficits. Data suggests that VAM plants acclimate more efficiently to water stress because of more frequent or extreme drought.

J. Amer. Soc. Hort. Sci. 109(2): 210-213. 1984.