Temperature effects on photosynthesis in gametophytic and sporophytic stages of the freshwater red alga Sirodotia delicatula (Rhodophyta, Batrachospermales) under a global warming perspective

Abstract

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.

Effect of glyphosate-based herbicides on the photosynthetic responses of the macrophyte Egeria densa Planch. from topical lotic ecosystems

“…wrightii decreased as a function of increased DRR under exposure to the herbicide. The significant increase in DRR values, which, in turn, negatively impacts the NPR, suggests that E. densa experiences relevant physiological stress and increases in metabolic rate when exposed to Roundup ® (Kramer et al, 2004;Klughammer & Schreiber, 2008;Vilas Boas et al, 2018). The indication that exposure to Roundup ® produces significant physiological stress in E. densa, which was observed from the data from the dissolved oxygen evolution technique and chlorophyll a content, apparently conflicts somewhat with data from the Chl-a fluorescence measurements.…”

“…Experiments using dissolved oxygen evolution were performed to calculate the net photosynthetic rate (NPR) and dark respiration rate (DRR), and they followed the procedures described by Necchi Júnior (2004aJúnior ( , 2004b, Oliveira et al (2016), andBranco et al (2017), while experiments involving Chl-a fluorescence measurements were used to calculate specific photosystem II (PSII) performance parameters (Vilas Boas et al, 2018).…”