Tropical lotic primary producers: Who has the most efficient photosynthesis in low‐order stream ecosystems?

Abstract

Photosynthetic performance was assessed for the main groups of primary producers of low‐order tropical streams, comprising macroalgae (11 taxa of Chlorophyta, Rhodophyta and Xanthophyta plus Cyanobacteria), bryophytes (2), angiosperms (3), and the periphytic community, by means of the Chl‐a fluorescence and oxygen evolution techniques. Samples of primary producer were collected in nine stream reaches within the same drainage basin that were characterised as open or partially shaded. Low values of compensation irradiance (Ic) were found for all species tested, suggesting that they are able to maintain an autotrophic metabolism even under very low irradiances. Parameters derived from photosynthesis–irradiance curves revealed high values of the saturation parameter (Ik), associated with relative low values of photosynthetic efficiency (αETR) and photoinhibition (βETR) for species of Chlorophyta and the periphyton, suggesting adaptation to high irradiance conditions. Species of Rhodophyta, Xanthophyta, Bryophyta and angiosperms showed, in general low values of Ik and moderate to high values of αETR and βETR, indicating typical photosynthetic responses of shade‐adapted plants. Chlorophyta and the periphyton showed high photosynthetic efficiency in high irradiance, and rhodophytes, bryophytes and angiosperms seemed to be more efficient in shaded stream stretches. Considering that Cyanobacteria showed high values of the photosynthesis/respiration (P/R) ratio, we suggest that this group is the most efficient primary producer in a wide range of low‐order tropical streams. This physiological trait could be a feature that favours the abundance of Cyanobacteria in the benthic primary producer community, as is often reported in the literature.

Stream macroalgal flora from Parnaíba River Basin, Brazil: reducing Wallacean shortfall

“…Most surveys cited above include disturbed regions or open riparian vegetation. It appears that this predominance of green algae species in these regions occurs due to the better adaptation of the group to high light intensity regimes due to characteristics of its photosynthetic complex (Branco et al 2017). Although Bacillariophyta was not the richest group, in this study a bigger number of diatom species was found than conventionally for stream macroalgae studies (e.g.…”

Macroalgas de riachos na Serra do Japi, sudeste do Estado de São Paulo, Brasil

“…Os representantes desse grupo algal apresentam um tipo de adaptação cromática que permite a presença, muitas vezes predominante, de espécies de cianobactérias independentemente do nível de luminosidade (Necchi 2004, Tonetto et al 2012. Além disso, Branco et al (2017) demonstraram que representantes desse grupo de algas apresentaram altos valores da razão fotossíntese/respiração em uma ampla variedade de tipos de riachos, mesmo quando comparados com outros grupos algais, ou mesmo espécies de briófitas e macrófitas aquáticas. Assim, as cianobactérias podem apresentar vantagens ecológicas que superam algumas limitações ambientais, como, por exemplo, o sombreamento e, permite, portanto, uma importante contribuição a produtividade de riachos tropicais mesmo em diferentes tipos de paisagens (Branco et al 2017).…”

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

“…After cleaning, plants were incubated in sterilized 110 mL Erlenmeyer flasks containing 100 mL of sterilized Bold's basal medium for a 3-day acclimation period in a B.O.D. incubator (Nova Ética brand, model 411/FDP355) under the same temperature (20 ± 0.5 °C), irradiance (140 ± 15 μmol m -2 s -1 ), and photoperiod (12/12 h) that were used in the experimental analyses (Branco et al, 2017). The irradiance to which the plants were subjected was continuously measured with a quantometer, Li-Cor model LI-189 (Lincoln, Nebraska, USA), coupled to a spherical quantum sensor, LI-193 SA.…”

“…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).…”

“…Although sometimes considered a model of invasive exotic species and a nuisance for reservoirs, especially those related to hydroelectricity generation (Bini et al, 1999;Uieda & Marçal, 2020), Egeria densa is a widely distributed freshwater plant that is native to Brazil, and it is an important primary producer in some lotic habitats (Branco et al, 2017). In addition, E. densa has been identified as having an important role as a habitat for other organisms, such as algae, zooplankton, and juvenile fishes (Pelicice & Agostinho, 2005).…”