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

Abstract

The activity of allelochemicals in agroecosystems are 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 allelochemicalmediated 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.

Dynamic Effect of Fresh and Aged Biochar on the Behavior of the Herbicide Mesotrione in Soils

“…Enhancement of mesotrione persistence was also observed after the addition of green compost and sewage sludge to soil, and it was attributed to an increase in herbicide sorption . This phenomena has been frequently described for the dissipation of pesticides in soils amended with BC, , although not always does the addition of organic amendments increase the persistence of particular compounds, because in some cases microorganisms prefer to use the organic amendment as a carbon source …”

“…There was a progressive increase in the sorption, which was not observed in the rest of treatments (Figure ). This can reasonably be attributed to slow sorption kinetics on BC particles. , Nevertheless, at 7 days, the amount of mesotrione sorbed was similar for all cases except for the fresh BC-amended soil ( p > 0.05). However, it has to be considered that at this time of the experiment, mesotrione soil residues in ABC_WI-amended soil were 2-fold greater than in the other treatments ( p < 0.05), which would explain the greater TD 50 value.…”

“…22 This phenomena has been frequently described for the dissipation of pesticides in soils amended with BC, 44,51 although not always the addition of organic amendments increases the persistence of a particular compounds, since in some cases microorganisms prefer to use the organic amendment as a carbon source. 52 The sorption percentage of mesotrione from the total amount extracted at different incubation times is shown in Figure 5. It is worthy to highlight that the non-recovered amounts are considered non-bioavailable, due to degradation or strong sorption.…”

Biochar changes the bioavailability and bioefficacy of the allelochemical coumarin in agricultural soils

“…Soil dissipation of coumarin was very fast for both doses tested, which is typical of natural allelopathic compounds and is the main drawback for their potential use as biopesticides 50 . For this reason, strategies to increase their persistence in soils are vitally needed 8,9,40 …”

“…S2). Previously, Pyrex® glass tubes containing 4 g of each soil were autoclaved (20 min, 121 °C and 200 kPa) with later incubation of the samples at 25 °C for 24 h. The treatment was performed for three consecutive days to ensure the complete sterilization of the samples 40 . After autoclaving, the samples were equilibrated (24 h, 20 ± 2 °C) with sterilized aqueous solutions of coumarin (8 mL) with initial concentrations ranging from 0.1 to 5 mg L –1 .…”