ACTA BOT. CROAT. 77 (2), 2018 135 Acta Bot. Croat. 77 (2), 135–140, 2018 CODEN: ABCRA 25 DOI: 10.2478/botcro-2018-0010 ISSN 0365-0588 eISSN 1847-8476 Photosynthetic performance of two freshwater red algal species Tamás Pálmai1*, Beáta Szabó2, Katalin Eszter Hubai1, Judit Padisák1,2 1 Department of Limnology, University of Pannonia, Egyetem u. 10, Veszprém 8200, Hungary 2 MTA-PE Limnoecology Research Group, Egyetem u. 10, Veszprém 8200, Hungary Abstract – Photosynthetic performances of two freshwater red algal populations from freshwaters of the Car- pathian basin were measured in this study. Populations were collected from different habitats: Bangia atropur- purea from Lake Balaton and Batrachospermum gelatinosum from the Tapolca stream. Their photosynthesis was studied in a wide range of temperature (5–35 °C) and light intensity (0–1150 µmol m–2 s-1) in a photosynthetron. We found both species’ photosynthesis maxima at 25 °C but B. atropurpurea had significantly higher photosyn- thetic production. Low and medium values were calculated for the species’ photoadaptation parameters. Com- pensation light intensities determined in this study were similar to those obtained in previous studies. Both species utilized light efficiently; photoinhibition was detected only at two measuring temperatures for Bangia and at four measuring temperatures for Batrachospermum. P-T characteristics of the species revealed that both have temperature optima at 25 °C under high and medium light intensities but there are no such remarkable optima at low irradiance. The biomass specific respiration of both species increased with increasing tempera- ture. We confirmed the good light utilization of these red algal species but found temperature optima higher than reported previously. Keywords: Bangia atropurpurea, Batrachospermum gelatinosum, ecophysiology, light, photosynthetic characteris- tics, temperature Abbreviations: Ps – maximal production obtained in the absence of photoinhibition, PBmax – biomass specific maximal photosynthetic rate, Ik – photoadaptation parameter, Ic – compensation light intensity, α – initial slope of the curve, light utilization, β – photoinhibition parameter, RB – biomass specific respiration. * Corresponding author, e-mail: palmait@almos.uni-pannon.hu Introduction Red algae are mostly marine macroscopic organisms. Be- sides the 5000–5500 marine Rhodophyta species there are about 180 species living in fresh waters; most are limited to running waters. They are often considered as indicators of good water quality and clean habitats as they prefer very clear, transparent habitats (Skuja 1938, Sheath 1984). Ban- gia atropurpurea (Mertens ex Roth) C. Agardh and Batra- chospermum gelatinosum (Linnaeus) De Candolle are fila- mentous red algae with worldwide distribution, commonly growing attached to the surface of shoreline rocks of lakes and streams. Bangia atropurpurea is an unbranched filamentous red alga that grows along rocky shorelines. The species occurs both in fresh- and seawater. It was often mentioned under the name B. fuscopurpurea (Dillw.) till Geesink (1973) con- cluded that these two taxa are conspecific. B. atropurpurea was described in North America, Europe, the Middle East, and in Japan (Belcher 1960, Geesink 1973, Sheath and Cole 1980, Araki et al. 1994, Barinova 2013). Barinova (2013) found B. atropurpurea in a wide range of temperature (15.5– 35 °C), pH (6.6–8.0), and conductivity (0.82–4.0 mS cm–1). Temperature and day length dependence of the growth rate, maturation and size of the species were also reported (Som- merfeld and Nichols 1973). Monospore germination of B. at- ropurpurea is light-dependent (Charnofsky et al. 1982). Op- timum conditions for the photosynthesis were found at 20 °C and 750 µmol m–2 s–1 (Graham and Graham 1987). Batrachospermum gelatinosum is widely distributed in the running waters of North America and Europe. Popu- PÁLMAI T., SZABÓ B., HUBAI K. E., PADISÁK J. 136 ACTA BOT. CROAT. 77 (2), 2018 lations, as red algae usually, occur at cold temperatures (0–22 °C) in circumneutral (pH 6–8.5) waters with low con- ductivity (10–490 µS cm–1) (Kremer 1983, Vis et al. 1996, Vis and Sheath 1997, Carmona et al. 2011, Chiasson et al. 2014, Drerup and Vis 2014). B. gelatinosum was also described in Central and South America, Australia and in the Middle East under similar conditions (Vis and Entwisle 2000, Jiménez et al. 2004, Vis et al. 2008, Barinova 2013). Besides the dis- tribution, the physiology of some Batrachospermum species (B. ambiguum, B. delicatum, B. gelatinosum, B. helmintho- sum and B. vogesiacum) were also studied. It was shown that low irradiance is advantageous for the growth of red algae species. Species-specific temperature optima of the growth were established by Zucchi and Necchi (2001) and Drerup et al. (2015). Our knowledge about the Hungarian red algae flora is quite limited. The total number of taxa recorded in North- ern European countries is higher than that in Central- and South-Europe. In Hungary, nine taxa were reported (Kwan- drans and Eloranta 2010), two of these (Batrachospermum ectocarpum Sirodot and B. moniliforme Roth) were found in the springs of the Northern Bakony Mountains (Kol 1968). Additionally, some species (Audouinella ciolacea (Kütz.) Hamel, Audouinella chalybea, Chroodactylon ornatum (Ag.) Basson, Hildebrandia rivularis (Lieben) Ag., Porphyridium purpureum (Bory) Drew et Ross, Thorea hispida) were re- ported from the two main rivers (Danube and Tisza) (Kiss and Pelyhe 2004, Szemes 1967, Uherkovich 1957). Extend- ed stands of Bangia atropurpurea were described from the shoreline rocks of Lake Balaton (Tamás 1959) but, as a con- sequence of eutrophication, the species was suppressed in the last decades (Kiss and Pelyhe 2004). As a consequence of restoration measures (Istvánovics et al. 2007), B. atropur- purea reappeared in early spring, 2015 offering an opportu- nity to study its photosynthetic performance. Because of our scarce knowledge about the Hungarian red algae and a lack of physiological data, measurements were carried out to determine not only the temperature and light intensity optima but also the tolerance range of the pop- ulations. For this reason, we carried out experiments in a wide range of temperature and light conditions. Materials and methods Two populations of freshwater red algae were investigat- ed in this study. Samples were collected during the period of highest abundance from surfaces of stones then were kept in filtered (0.45 µm pore size membrane filter) stream or lake water depending on sampling site. Bangia atropurpurea was collected from shoreline rocks of Lake Balaton in February 2015 (water temperature was 4.9 °C) (46°54'53.9928" N, 17°53'34.4148" E). Lake Balaton is the largest shallow lake in Central Europe, with slightly alkaline water (pH~8.3). The dominant ions of the lake are Ca2+, Mg2+ and HCO3–, and Secchi transparency rarely ex- ceeds 1 m. Long sections of the lake’s shoreline are artificially covered by large red sandstone bricks to protect the shore- line constructions against wave action. These rocks provide suitable habitats for B. atropurpurea. Batrachospermum gelatinosum was collected from the Tapolca stream (46°51'1.224" N, 17°25'17.8248" E) in April 2015. The stream is fed by hot springs. Its temperature var- ies between 9.6 and 21 °C during the year and it cools down only slightly in winter. During the sampling, water tempera- ture was 16.1 °C. Small and medium size stones (5–15 cm) cover the streambed; red algae grew attached to the surface of this substrate. The following physical parameters were recorded dur- ing samplings: temperature, pH, dissolved oxygen concen- tration, oxygen saturation and conductivity with HQ40d Portable Multi-Parameter Meter (Hach Lange) and Intel- liCAL™ PHC101 Rugged Gel Filled pH Electrode, Intelli- CAL™ CDC401 Rugged Conductivity Probe, IntelliCAL™ LDO101 Rugged Luminescent/Optical Dissolved Oxygen (LDO) (Tab. 1). Photosynthesis measurements were carried out in a pho- tosynthetron developed by Üveges et al. (2011), which allows measurements at nine different light intensities at the same time at a given temperature. Light intensities were set be- tween 0–1150 µmol m–2 s-1 (0, 15, 35, 75, 150, 300, 600, 800, 1000 µmol m–2 s–1 were used for Bangia and 0, 10, 30, 75, 130, 200, 420, 1150 µmol m–2 s–1 were used for Batrachospermum), PAR was provided by daylight tubes (Tungsram F74). Light intensities in the different cells were measured with a spheri- cal (4 π) quantum sensor. A wide range of temperature was used to determine not only the temperature optima but also the tolerance ranges of the species. Incubation temperature was increased by 5 °C increments in the temperature range 5–35 °C. Permanent temperature was provided by Neslab RTE-211. Red algal samples were filtered onto 1.2 µm pore size GFC filters, and then fresh weight was measured with 0.1 mg accuracy. Known fresh weights of the field samples were placed into Karslruhe-flasks, which were then filled with fresh filtered (0.4 µm pore size mixed cellulose-ester mem- brane filter) stream or lake water before each measurement. Prior to the experiments, samples were pre-incubated at least for 2 h at each measuring temperature. Photosynthetic Tab. 1. Environmental data measured at sampling sites. Tapolca-stream Lake Balaton Collected species Batrachosper- mum gelatinosum Bangia atropurpurea Date 20 April 2015 16 February 2015 Location 46°51'1.224"N 17°25'17.8248"E 46°54'53.9928"N 17°53'34.4148"E Temperature (°C) 16.1 4.9 pH 7.61 8.5 Dissolved oxygen (mg L–1) 9.19 12.17 Oxygen saturation (%) 93.7 94.9 Conductivity (µS cm–1) 704 565 PHOTOSYNTHESIS OF TWO RHODOPHYTA SPECIES ACTA BOT. CROAT. 77 (2), 2018 137 The increase of the PBmax was about 75–80% for both species and both had maxima at 25 °C. A remarkable difference was found between the photosynthetic production levels of the species. The highest PBmax of Batrachospermum was 0.683 µg C µg–1 FW h–1 in contrast to Bangia, which exhibited a photo- synthetic production higher by an order of magnitude (PBmax = 8.171 µg C µg–1 FW h–1). At 35 °C, the highest experimental temperature, both species’ photosynthetic activity dropped. The PBmax of Bangia decreased at 35 °C but it was still remark- able. The drop in the photosynthetic activity of Batrachosper- mum was about 95%, and gross photosynthetic activity at 35 °C was detected only at five light intensities. Ps values of Bangia were calculated only at 5 and 10 °C because at higher temperatures photoinhibition was not ob- served, and the obtained data were similar to PBmax. In the Ps values of Batrachospermum, differences were found: contrary to PBmax, Ps values increased with temperature and reached the highest value at 30 °C (1.195 µg C µg–1 FW h–1). A de- crease was observed only at the highest temperature (35 °C) but this drop was remarkable. Photoadaptation parameters (Ik) of Bangia varied be- tween 61.6 and 275.1 µmol m–2 s–1. They increased with the increasing temperature till 25 °C. At higher temperatures a slow decrease was observed in the Ik values. Ik values of Batrachospermum were lower and ranged from 32 to 165.8 µmol m–2 s–1. The highest value was found at 30 °C. Light utilization (α) of Bangia decreased with increasing temperature and changed between 1.39 × 10–2 and 3.26 × 10–5 µg C µg–1 FW h–1 (µmol m–2 s–1)–1, which means that the efficiency of light utilization of the species decreased with increasing temperature. α parameters of Batrachospermum also decreased along the temperature gradient: it varied from 6.8 × 10–3 to 9 × 10–4 µg C µg–1 FW h–1 (µmol m–2 s–1)–1. Photoinhibition (β) was not observed at any of the ap- plied temperatures. Bangia showed photoinhibition at a low- er part of the temperature range (5–10 °C): β was 6 × 10–4 and 1.5 × 10–3 µg C µg–1 FW h–1 (µmol m–2 s–1)–1. In contrast, Batrachospermum had β values at almost each measuring activity of the species were followed by measuring dissolved oxygen concentration (DO) with an IntelliCAL™ LDO101 sensor (Hach Lange). After the pre-incubation period, DO was measured at the beginning, then after 1 h and 2 h. The special design of the Karlsruhe-flasks prevents gas exchange with the environment. In the case of both species, measure- ments were conducted in three replicates at each of the nine light intensities. Respiration, gross- and net photosynthesis were deter- mined according to Wetzel and Likens (2000). Two equa- tions were used to determine the following photosynthetic parameters of the species: biomass specific maximal photo- synthetic rate (PBmax), maximal production obtained in the absence of photoinhibition (Ps; without photoinhibition it is equal to PBmax), photoadaptation parameter (Ik), compen- sation light intensity (Ic), initial slope of the curve (α), bio- mass specific respiration (RB). In the absence of photoinhi- bition, photosynthetic parameters were calculated according to Webb et al. (1974). If photoinhibition was observed, pho- toinhibition parameter (β) was also calculated according to Platt et al. (1980). Curves were fitted using GraFit software (Leatherbarrow 2009). To determine the compensation light intensity (Ic), a reordered form of the equation of Webb et al. (1974) was used in each case: I P R P C S B S� � � � � � ���� � � ln 1 � where Ic is the light intensity at which photosynthetic production becomes equal to respiration. Results Photosynthesis-light intensity characteristics The biomass specific maximal production (PBmax) of the species increased in parallel with the temperature (Figs. 1, 2). Fig. 1. Gross photosynthesis–irradiance (P–I) curves of Bangia atropurpurea measured along a temperature gradient. Data are average mean ± SD, n= 3. Fig. 2. Gross photosynthesis–irradiance (P–I) curves of Batra- chospermum gelatinosum measured along a temperature gradient. Data are average mean ± SD, n= 3. PÁLMAI T., SZABÓ B., HUBAI K. E., PADISÁK J. 138 ACTA BOT. CROAT. 77 (2), 2018 temperature including the higher temperature range (20–35 °C). They varied between 4.6 × 10–5 and 1.1 × 10–3 µg C µg–1 FW h–1 (µmol m–2 s-1)–1. Respiration of both species increased with tempera- ture. This increase was higher than 90% for both species. Although Bangia had a higher biomass specific respiration, these values for the two species were much more similar than their biomass specific productions. Photosynthesis-temperature characteristics Plotting the mean values of photosynthetic activity as a function of the temperature (P–T), it is possible to examine the temperature dependence of the photosynthesis at each light intensity. In the 75–1000 µmol m–2 s–1 light intensity range biomass specific productions of Bangia atropurpurea increased with the temperature and reached a maximum at 25 °C (Fig. 3.). Besides, at the highest temperatures (30 and 35 °C) a decrease was found. The highest level of photosyn- thesis was observed at 600 µmol m–2 s–1. At lower light inten- sities (35 and 15 µmol m–2 s–1) outliers were found at 10 °C. At light intensities between 1150 and 130 µmol m–2 s–1, the biomass specific maximal production of Batrachosper- mum showed normal distribution and had maxima at 20 and 25 °C (Fig. 4.). At 75 µmol m–2 s–1, PBmax of the species reached the highest value at 15 °C and after a slight decrease a remarkable drop was found at 35 °C. At low light inten- sities (30–10 µmol m–2 s–1), PBmax maxima were detected at the lowest temperature (5 °C) and a slight decrease was ob- served. Under low light conditions at the highest measuring temperature (35 °C), gross- and net photosynthetic activity were not observed. Discussion Physiological optima of different red algal species are thoroughly studied worldwide. Temperature and light inten- sity optima of the different species were determined in sev- eral studies (On-line Suppl. Tab. 1). Adaptation to low light intensity and temperature has been reported both for Batra- chospermum gelatinosum and for Bangia atropurpurea (Som- merfeld and Nichols 1973, Geesink 1973, Necchi and Zucchi 2001, Necchi and Alves 2005). Since previous studies applied many different and inconvertible units, direct comparisons are difficult. However, it is possible to compare trends. In contrast to many other red algae, Bangia atropurpurea is a well-studied species. Low temperature and light intensi- ty are considered the optimal conditions for the species. Be- cause Rhodophyta species are commonly found at low tem- Fig. 3. Gross photosynthesis–temperature (P–T) curves of Bangia atropurpurea measured at high (A) and low (B) incubation light intensities. Data are average mean ± SD, n= 3. Fig. 4. Gross photosynthesis–temperature (P–T) curves of Batra- chospermum gelatinosum measured at high (A) and low (B) incu- bation light intensities. Data are average mean ± SD, n= 3. PHOTOSYNTHESIS OF TWO RHODOPHYTA SPECIES ACTA BOT. CROAT. 77 (2), 2018 139 peratures and light intensities, most previous experiments were limited to low temperature and light intensity rang- es (On-line Suppl. Tab. 1). In most cases, these values var- ied between 9–20 °C and 4–200 µmol m–2 s–1 (Belcher 1960, Geesink 1973, Sommerfeld and Nichols 1973, Sheath and Cole 1980, Charnofsky et al. 1982). Graham and Graham (1987) carried out laboratory experiments on growth and reproduction of Bangia in a wide range of temperatures and light intensities. Their finding that Bangia has a tempera- ture optimum at 20 °C and a light intensity optimum at 750 µmol m–2 s–1 differs from previous findings as well as from our observations. The extremely high light optimum should be a result of the different data analysis. Our results regard- ing temperature preferences are similar to those of Graham and Graham (1987): we found a temperature optimum for photosynthetic production at 25 °C. This temperature is much higher than the usual cultivating temperatures and other findings reported previously. As to light preferences, we found a maximum of 275 µmol m–2 s–1 in Ik values at 25 °C. Light utilization of the species decreased with the increasing temperature, which suggested an acclimation to low light in- tensity and temperature in agreement with the previous find- ings (Sheath 1984). Photoinhibition was found only at low temperatures (5–10 °C) in contrast to Graham and Graham (1987). Even though they did not do the calculations, their results suggest that Bangia sp. had photoinhibition at elevat- ed temperatures (20–30 °C). Batrachospermum gelatinosum, like red algae in gener- al, occurs in cold, clean running waters (7–14 °C), Kremer (1983), Vis et al. (1996), Vis and Sheath (1997), Drerup and Vis (2014) and we also found it under such conditions (Tab. 1). Several experiments were carried out on the photosynthe- sis of different Batrachospermum species. In accordance with our results, Kremer (1983) found a temperature optimum at 20–25 °C for the photosynthetic production of Batracho- spermum sp. when a short temperature adaptation time was used before measurement; however, Kremer (1983) found a lower temperature optimum (15 °C) if the adaptation time was longer, and suggested that the use of a longer adapta- tion time is needed. Necchi and Zucchi (2001), Zucchi and Necchi (2001), Necchi and Alves (2005) and Drerup et al. (2015) investigated Rhodophyta species, including Batracho- spermum species (On-line Suppl. Tab. 1). Zucchi and Necchi (2001) found growth optimum for Batrachospermum species at 20 °C along with a preference for low light intensity (65 µmol m–2 s–1). Necchi and Zucchi (2001), Necchi and Alves (2005) and Drerup et al. (2015) conducted photosynthesis measurements at 20 °C and found differences between Ba- trachospermum species light optima for photosynthetic pro- duction. Ik values varied between 6 and 76 µmol m–2 s–1 which is lower than our findings at this temperature (122 µmol m–2 s–1). As to compensation light intensity, Ic values varied be- tween 2 and 16 µmol m–2 s–1 , which was similar to data by Necchi and Zucchi (2001), Necchi and Alves (2005) and Dr- erup et al. (2015). Confirming previous publications, we also found a high level of light utilization and photoinhibition at 20 °C (Necchi and Zucchi 2001, Necchi and Alves 2005, Dr- erup et al. 2015). In comparison to ecophysiological data of species oth- er than Rhodophyta, it is apparent that most species have photosynthesis maxima at higher temperature (e.g. Üveges et al. 2012, Pálmai et al. 2013, Lengyel et al. 2015, Pálmai et al. 2016) than these two Rhodophyta populations. Sim- ilar Ik values were found for Microcystis aeruginosa, Mer- ismopedia tenuissima and Oscillatoria sp. (Coles and Jones 2000), Porphyra species (Lin et al. 2008), Aphanizomenon flos-aquae (Üveges et al. 2012), Nitzschia frustulum (Lengyel et al. 2015), but there are also species with lower (Picocystis salinarum (Pálmai et al. 2013), and with higher photoadap- tation parameters, like Arthrospira fusiformis (Pálmai et al. 2013), Microcystis flos-aquae (Pálmai et al. 2016). Similarly, efficient light utilization was reported for Rhodophyta spe- cies (Necchi and Zucchi 2001, Necchi and Alves 2005, Dre- rup et al. 2015) but also good utilization was determined for Aphanizomenon flos-aquae (Üveges et al. 2012) and for Pi- cocystis salinarum (Pálmai et al. 2013). Acknowledgement This research was supported by the Hungarian Nation- al Research, Development and Innovation Office (NKFIH K-120595). 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