Cinnamic acids in plant-soil interactions: a microcosm experiment

In soil naturally occurring phenolic acids act as allelochemicals and are involved in several plant-soil interactions. In the present study, a microcosm-style experiment was used to investigate the allelopathic responses induced by individually applied ferulic, trans-cinnamic, p-coumaric and caffeic acids on the root system of maize seedlings grown for 12 days under controlled conditions in a sterile soil:perlite (70:30 v/v) mixture. This simplified model ecosystems are valuable tools in developing hypothesis about soil-plant interactions. The fate of the phenolic acids in the growing medium was preliminarily assessed by their recovery after soil incubation assays. Adsorption data showed that a time-dependent equilibrium process was reached after 96-h incubation and the available amount of phenolic acids declined with time according to the following scheme: caffeic > trans-cinnamic > p-coumaric > ferulic acids. In order to maintain a constant concentration of available phenolic acids (0,1 µmol g-1 dw) at the soil-perlite mixture interface, an aqueous solution of each acid was added on 0, 2, 4, and 8 days from transplant. The morphology of the whole root system and of the different root types (primary, seminal, nodal, lateral of the primary and seminal roots) was evaluated considering the following parameters: total root length, biomass allocation, root fineness and tissue density. Here were reported the effects on maize root system induced by trans-cinnamic and ferulic acids. Trans-cinnamic acid exerted a more marked and rapid action in reducing the total root length showing also a selective action towards the different root types than ferulic acid. Further, trans-cinnamic acid affected both biomass allocation towards the root and root fineness and tissue density; whereas ferulic acid mainly influenced the root fineness. Results suggested: i) a specific response of maize root system in relation to the allelochemical and time of exposure; ii) maize root types showed a different response to the phenolic acids, and iii) and their morphological parameters were selectively affected.