Although macroalgae are considered one of the most important primary producers in streams, to our knowledge there has been no research on the effects of herbicides on these organisms. Such studies are crucial for improving our understanding of the impact of these substances on stream ecology. In this study, we assess the effects of technical-grade glyphosate, Roundup and aminomethylphosphonic acid (AMPA; the main degradation product of glyphosate) on the photosynthetic rate, dark respiration rate and chlorophyll a content of Nitella microcarpa var. wrightii, a green algae found worldwide. Three concentrations of technical-grade glyphosate and Roundup were tested (0.28, 3.5 and 6 mg l À1 ), while for AMPA only one concentration was evaluated (0.03 mg l À1 ). Our results indicate that glyphosate has a stronger inhibitory effect on photosynthetic rate when applied in association with a surfactant (Roundup). These effects are related both to the concentration of the active ingredient and to exposure time. On the other hand, treatment with AMPA had a stimulatory effect on the photosynthetic rate, which may be associated with an increased supply of phosphorus available to the algae from the AMPA degradation process. From an ecological perspective, our results show that the ecological distribution of N. microcarpa var. wrightii, in terms of both spatial and temporal scales, can be affected by glyphosate-based herbicides in streams.

SUMMARY The increase in Earth's global mean temperature due to human influence has become a major concern, with ecological consequences already being reported around the world. In tropical streams, benthic red algae belonging to the order Batrachospermales contribute to a large fraction of the community energy input and play an important role in sustaining autotrophic food webs. The Batrachospermales also have a unique life history, with heteromorphic life stages (gametophytes and sporophytes) occurring seasonally and with distinct ecological roles. Through “in vivo” chlorophyll fluorescence and dissolved oxygen evolution techniques, we evaluated the effects of projected temperature increases of two future scenarios (RCP 4.5 and RCP 8.5) on the photosynthetic response of Sirodotia delicatula gametophytes and sporophytes. In general, both chlorophyll fluorescence and dissolved oxygen showed that the RCP 8.5 scenario could severely jeopardize the photosynthetic performance of the sporophytes during the summer while also providing a stressful physiological situation to the gametophytes. Due to the crucial role of sporophytes in the development of this species, results indicate that this predicted scenario could affect this species. Given the position of these organisms at the base of the food web in tropical lotic environments, especially in shaded low‐order streams, such impact could generate unforeseen cascade effects on higher trophic levels.

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Effect of glyphosate-based herbicides on the photosynthetic responses of the macrophyte Egeria densa Planch. from topical lotic ecosystemsThe effects of pesticide pollution on eco-physiological responses in primary producers are understudied. To partly overcome this gap, this study evaluated the effects of a glyphosate-based herbicide, Roundup ® (three nominal concentrations: 0.28 mg/L [Treatment T0.28]; 3.5 mg/L [T3.5]; and 6 mg/L [T6]), and its main degradation product, aminomethylphosphonic acid (AMPA) (0.03 mg/L [T0.03]), on the photosynthetic responses of an aquatic macrophyte species, Egeria densa Planch. The net photosynthetic rate (NPR) and dark respiration rate (DRR) were evaluated by the dissolved oxygen evolution method, while some PSII performance parameters were measured by a Chl-a fluorescence-based method. Additionally, the chlorophyll a content was measured. The experimental data showed that E. densa had significant losses in photosynthetic efficiency under Roundup ® and AMPA exposure, with reductions in the NPR (reduction of -61 % for T3.5; -90 % for T6; and -161 % for T0.03, compared to control) and chlorophyll a content (-82 % for T0.28, -79 % for T3.5, -82 % for T6, and -28 % for T0.03) and increases in the DRR (+150 % for T3.5, +130 % for T6, and +271 % for T0.03). The results from the Chl-a fluorescence measurements registered statistically significant differences between the Roundup ® treatments and the control group for the effective quantum yield (+56 % for T0.28, +43 % for T3.5, and +56 % for T6) and for non-photochemical extinction (+67% for T0.28, +73 % for T3.5, and +59 % for T6). Taken together, the findings of the experiments with E. densa indicate that the negative effects from the glyphosate-based herbicide Roundup ® on primary producers might be common and widespread in tropical and subtropical aquatic environments in Brazil.

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