Continuous glyphosate applications affect plant development of mangrove species from coastal wetlands: Rhizophora mangle and Pachira aquatica

Glyphosate based herbicides not only affect unwanted plants in agricultural and urban areas, but also impact non-target vegetation, including its associated biome. The effect of the repeated application of these products on growth remains undetermined for many ecologically important trees. Coastal wetlands accumulate pollutants and therefore are exposed to different compounds at varying concentrations. This exposure may interfere with wetlands' ability to maintain essential ecosystem functions. Therefore, this study aimed to evaluate the effect of different concentrations of a commonly used glyphosate-based herbicide on mesocosms planted with juvenile Rhizophora mangle and Pachira aquatica. We assessed the impact of herbicide treatment on plant growth as well as the subsurface CO2 efflux. Plants were transplanted to containers filled with fine gravel (substrate) and maintained under flooded conditions. Four different glyphosate treatments were investigated over a period of 124 days: in three treatments, glyphosate was added in two applications of either 25, 50, or 100 mg glyphosate acid equivalent (ae)/L, whereas in the fourth treatment, glyphosate was added in eight applications of 25 mg ae/L. Plant growth was measured (plant height, stem diameter, number of green leaves or leaflets) and subsurface CO2 efflux from the substrate was quantified. Different glyphosate concentrations resulted in different effects on plant growth for both species. Mesocosms that received continuous glyphosate applications exhibited reduced plant growth in the long term. Carbon dioxide efflux was reduced by different glyphosate concentrations. Our results contribute to further understanding the adverse impact that glyphosate-based products may have on ecologically important trees and their ecosystem services in coastal areas in the tropics.