Modulation of the non-target phytotoxicity of glyphosate by soil organic matter in tomato (Solanum lycopersicum L.) plants

Glyphosate (GLY)-based herbicides are the most widely used and, although it is admitted that, when in contact with the soil, GLY degrades rapidly, recent studies show that the accumulation of its residues in soils can negatively affect the growth of non-target crops. Knowing that soil properties, such as organic matter (OM) content, influence the bioavailability of pesticides, this study aimed to study the role of soil OM in preventing GLY phytotoxicity, using tomato (Solanum lycopersicum L.) as a model crop species. For this, plants grew for 28 d in soils with different concentrations of OM [2.5; 5.0; 10 and 15% (m/m)] contaminated, or not, by GLY (10 mg kg(-1)). Afterwards, biometric parameters, oxidative stress markers [lipid peroxidation (LP); hydrogen peroxide (H2O2); proline] and several physiological indicators [total sugars, amino acids and soluble proteins; glutamine synthetase (GS) and nitrate reductase (NR)] were evaluated. According to the results, GLY significantly reduced plant growth in all tested soils, especially in those with lower OM content (2.5 and 5.0%), this being accompanied by an upsurge of LP in shoots and proline in shoots and roots, and a decrease of total sugars in both organs. In contrast, the exposure of plants to GLY in OM-enriched soils (10 and 15%) did not substantially alter the cellular redox status, while contributing to a higher content of total amino acids in shoots. Nitrogen (N) metabolism-related endpoints were not substantially affected by GLY independently of the soil OM. Overall, the results seem to suggest that soils with a higher OM content, 10 and 15%, can mitigate the non-target phytotoxicity of GLY, possibly by decreasing herbicide bioavailability and/or by stimulating defence mechanisms, thereby improving crop growth and physiological performance.