Modulating the persistence and bioactivity of allelochemicals in the rhizosphere: salicylic acid, a case of study

The activity of allelochemicals in agroecosystems is highly dependent on their soil persistence. The aim of this work was to establish a link between the soil persistence of salicylic acid (SA) and its bioactivity, to better understand the mechanisms of allelochemical-mediated soil-plant interactions. Incubation and bioassay experiments were conducted for this purpose. The addition of HgCl2 and decreasing temperature to 4 °C increased the persistence of SA in soil. Since these treatments greatly decreased the soil respiration, they probably slowed the SA dissipation by reducing the soil microbial activity. To a lesser extent, soil humidity and soil pH also influenced the SA dissipation rate. Exogenous olive-mill organic waste (ALP) increased the soil respiration, but interestingly, delayed the degradation of SA, presumably because ALP acted as an alternative source of C for soil microorganisms. The phytotoxicity of SA towards Eruca vesicaria in soil increased by the addition of ALP. Applied to soil at 0.5%, ALP reduced the SA dose for 50% Eruca vesicaria aerial biomass inhibition to 40%. Our results show how certain agronomic practices, such as the application of agri-industrial biosolids, could be used to modulate the persistence of allelochemicals in the rhizosphere and control their biological functions in soils.