Matthieu Moingt

Impact of phosphate on glyphosate uptake and toxicity in willow

Phosphate (PO4(3-)) has been shown to increase glyphosate uptake by willow, a plant species known for its phytoremediation potential. However, it remains unclear if this stimulation of glyphosate uptake can result in an elevated glyphosate toxicity to plants (which could prevent the use of willows in glyphosate-remediation programs). Consequently, we studied the effects of PO4(3-) on glyphosate uptake and toxicity in a fast growing willow cultivar (Salix miyabeana SX64). Plants were grown in hydroponic solution with a combination of glyphosate (0, 0.001, 0.065 and 1 mg l(-1)) and PO4(3-) (0, 200 and 400 mg l(-1)). We demonstrated that PO4(3-) fertilization greatly increased glyphosate uptake by roots and its translocation to leaves, which resulted in increased shikimate concentration in leaves. In addition to its deleterious effects in photosynthesis, glyphosate induced oxidative stress through hydrogen peroxide accumulation. Although it has increased glyphosate accumulation, PO4(3-) fertilization attenuated the herbicides deleterious effects by increasing the activity of antioxidant systems and alleviating glyphosate-induced oxidative stress. Our results indicate that in addition to the glyphosate uptake, PO4(3-) is involved in glyphosate toxicity in willow by preventing glyphosate induced oxidative stress.

Lignin biomarkers signatures of common plants and soils of Eastern Canada

Lignin CuO oxidation byproducts have been successfully used as biomarkers to describe terrigenous organic matter (TOM) dynamics in the environment in particular to understand various pedological processes. The fact that the major lignin biomarkers data-set used in environmental studies in temperate zones across the globe is based on pure vegetal samples from the Northwestern U.S.A. constitutes a major drawback in this field of research. This study presents a new lignin biomarker data-set of common plant species and soil types from the forest domain of Eastern Canada. Our results show that lignin signatures in pure vegetal samples can be significantly different from those listed as references in the literature for the same plant type (angiosperm/gymnosperm) demonstrating that location is a crucial parameter to consider. We also present characteristic lignin signatures of boreal soils that have evolved from the taxon of tree that grow on such soils. Some watershed specificities such as the presence of Sphagnum can increase the difficulty to decipher lignin sources. Specifically determining lignin signatures for pure plants and corresponding soils in a region of study is recommended to effectively use lignin biomarkers to study TOM dynamics at the watershed scale of that region.

Environmental and Anthropogenic Factors Influencing Mercury Dynamics During the Past Century in Floodplain Lakes of the Tapajós River, Brazilian Amazon

In the Tapajós River region of the Brazilian Amazon, mercury (Hg) is a prevalent contaminant in the aquatic ecosystem. Few studies have used comprehensive chronological analyses to examine the combined effects of environmental and anthropogenic factors on Hg accumulation in sediments. Total mercury (THg) content was measured in sediments from eight floodplain lakes and Pb210 isotope analysis was used to develop a timeline of THg accumulation. Secondary data representing environmental and anthropogenic factors were analyzed using geo-spatial analyses. These include land-cover change, hydrometeorological time-series data, lake morphology, and watershed biophysical characteristics. The results indicate that THg accumulation and sedimentation rates have increased significantly at the surface of most sediment cores, sometimes doubling since the 1970s. Human-driven land-cover changes in the watershed correspond closely to these shifts. Tropical deforestation enhances erosion, thereby mobilizing the heavy metal that naturally occurs in soils. Environmental factors also contribute to increased THg content in lacustrine sediments. Climate shifts since the 1980s are further compounding erosion and THg accumulation in surface sediments. Furthermore, variations in topography, soil types, and the level of hydrological connectivity between lakes and the river explain observed variations in THg fluxes and sedimentation. Although connectivity naturally varies among sampled lakes, deforestation of sensitive floodplain vegetation has changed lake–river hydrology in several sites. In conclusion, the results point to a combination of anthropogenic and environmental factors as determinants of increased THg accumulation in tropical floodplain sediments in the Tapajós region.