Developing a glyphosate-bioremediation strategy using plants and actinobacteria: Potential improvement of a riparian environment

How do glyphosate and AMPA alter the microbial community structure and phosphorus cycle in rice-crayfish systems?

Glyphosate, a commonly used organophosphorus herbicide in rice-crayfish cropping regions, may alter regional phosphorus cycle processes while affecting the structure of microbial communities. However, the effects of glyphosate residues on rice-crayfish systems remain unclear. In this study, we assessed the spatial and temporal distribution characteristics of glyphosate and its primary degradation products, as well as the impact mechanisms of glyphosate on microbial communities and the phosphorus cycle in rice-crayfish systems such as paddy fields, breeding ditches and recharge rivers. The detection rates of glyphosate and aminomethylphosphonic acid (AMPA) were 100% in rice-crayfish systems. Concentrations of glyphosate in the water phase and soil/sediment were as high as 0.012 μg/L and 7.480 μg/kg, respectively, and concentrations of AMPA were as high as 17.435 μg/L and 13.200 μg/kg, respectively. Glyphosate concentrations were not affected by rainfall or sampling site, but concentrations of AMPA in the water phase of recharge rivers were affected by rainfall. The glyphosate concentration was significantly and positively correlated with RBG-16-58-14 abundance, and the AMPA concentration was significantly and positively correlated with Actinobacteria and Lysobacter abundance, and negatively correlated with Cyanobacteria abundance (P < 0.05). The highest abundances of phoD, phnK, and ppx genes were found in all soils/sediments. Glyphosate concentration in soil/sediment was significantly and positively correlated with the abundance of phoD gene encoding an organophosphorus-degrading enzyme and ppx gene encoding poly inorganic phosphate (Pi) hydrolase (P < 0.05). In addition, the glyphosate concentration was significantly and positively correlated with the Ca-bonded Pi content (P < 0.05). This implies that glyphosate may promote the production of stable Pi in rice-crayfish systems by increasing the abundance of phoD and ppx genes. The results of this study reveal the impact mechanism of glyphosate on the phosphorus cycle in rice-crayfish systems and provide a basis for the risk assessment of glyphosate.

Influence of land use on spatial distribution of mobile phosphorus forms in the sediment of a tropical semi-arid reservoir

Changes in land use and land cover influence the transport of nutrients, mainly phosphorus (P), to aquatic ecosystems. P can be available in the water column to primary producers' assimilation or be stored in different forms in limnic sediment. Therefore, this study aims to analyze the impact of land use and land cover on the spatial distribution of phosphorus forms in the sediment of a tropical semi-arid reservoir. We hypothesize that agriculture, exposed soil and the presence of floodable vegetation increase the amount of mobile phosphorus in the sediment and the sediment closer to the dam show a greater amount of mobile phosphorus due to the confluence of the flows. The classification of land use and land cover was carried out through supervised analysis at the level of the reservoir's drainage basin and area of influence. Sediment samples from the reservoir were collected at four different sampling points within the influence of two sub-basins. P forms were obtained through chemical fractionation of these sediment samples along the reservoir. Sparse Caatinga was the predominant land cover in the drainage basin and in the influence area, accounting for >50 % of these areas. This land cover represents a risk for nutrient transport to aquatic environments. The sediment samples from Boqueirão reservoir exhibited a high amount of phosphorus, mainly in the mobile forms. These forms were heterogeneously distributed throughout the reservoir. Agriculture activities, exposed soil, and floodable vegetation, influence the distribution and increase of mobile forms of phosphorus in the reservoir sediment. This suggests the need for specific strategies for manage these activities properly. Additionally, the sediment closest to the dam showed a lower amount of mobile phosphorus compared to samples further upstream.