Effects of multi-stressor environments on photosynthetic performance and oxidative stress of macroalgae from tropical lotic ecosystems: exposure to glyphosate-based herbicide under different scenarios of global warming

Abstract

Scientific evidence that stressors of anthropic origin can produce environmental problems on a global scale have been provided since the last century. In this context, the extensive use of agricultural chemicals associated with global warming has raised concern, given the possibility of exposing organisms to multi-stressor environments and, therefore, to even greater environmental risks. These concerns increase as the effects of exposure to multi-stressor environments affect primary producers in more vulnerable environments, such as macroalgae in lotic ecosystems. Considering this perspective, the present research project is being proposed to carry out a laboratory experiment in which tropical stream macroalgae will be exposed to a glyphosate-based herbicide, an active ingredient widely used in Brazil and in the world, in combination with global warming scenarios predicted by the Intergovernmental Panel on Climate Change (IPCC) in order to evaluate the effects of these multi-stress environments on the photosynthetic performance and oxidative stress of these organisms. The experimental treatments simulating multi-stressor environments will be defined based on paired combinations of three concentrations of glyphosate-based herbicide (0.28 mg e.a. L-1; 3, 5 mg e.a. L-1 and 6 mg e.a. L-1), plus the control group (0.0 mg e.a. L-1), and two future scenarios proposed by the IPCC (SSP2 -4.5 and SSP5-8.5), plus the control group (i.e., mean temperature (MT) of streams in the region where macroalgae will be collected), totaling 12 experimental treatments. The photosynthetic performance will be measured by the chlorophyll a fluorescence technique, considering the following photosystem II (PSII) parameters: i) effective quantum yield ("Y(II)"); ii) quantum yield of regulated non-photochemical energy loss ("Y(NPQ)"); iii) quantum yield of non-regulated non-photochemical energy loss ("Y(NO)") and iv) electron transport rate (ETR). Oxidative stress, in turn, will be measured by evaluating the activities of the enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and ascorbate peroxidase (APX, EC 1.11.1.11). Both photosynthetic parameters and enzymatic activities will be measured, in quintuplicate (n=5), after seven days of exposure and differences between multi-stressor treatments will be evaluated by two-way Analysis of Variance (ANOVA). (AU)