Effects of Root Exudates of Cucumber (Cucumis sativus) and Allelochemicals on Ion Uptake by Cucumber Seedlings

The effects of root exudates of cucumber, aromatic carboxylic acids in root exudates, and their analogs upon the uptake of NO₃, $H_2 PO_4^ - $ $SO_4^{2 - } $ K⁺, Ca²⁺, Mg²⁺, and Fe²⁺ by intact cucumber seedlings were examined. Root exudates inhibited the uptake of all the ions analyzed except for $H_2 PO_4^ - $ . Inhibition of ion uptake by cinnamic acid, a main component of root exudates, was both concentration- and pH-dependent. With decreasing pH, the inhibitory effect on the ion uptake increased. With benzoic and cinnamic acids, the substitution of hydrophilic group(s) on the benzene ring alleviated the inhibition of ion uptake. Aromatic acids enhanced ion leakage. The potency was in proportion, but not equal, to the extent of uptake inhibition. The lipophilicity was a valuable index for evaluating the allelopathic potential of aromatic acids.