Physiological response of temperate microphytobenthos to freezing temperatures

2022

J. Mar. Biol. Ass.

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Microphytobenthos (MPB) communities are responsible for most primary production in shallow intertidal mudflats. The effects of short-term changes in temperature and light (1200, 500 and 0 μmol photons m−2 s−1) on the photosynthetic activity of intertidal MPB communities of Browns River, Tasmania, during winter (0, 5, 10 and 15°C) and summer (20, 25, 30, 35 and 40°C) were examined using a Pulse Amplitude Modulated (Water PAM) fluorometer. The MPB communities were primarily dominated by the diatom genera Navicula, Cocconeis and Amphora, with a difference in species dominance during seasons. During summer, Amphora coffeaeformis dominated communities were significantly impacted by temperatures above 30°C regardless of light intensities. The MPB was able to photosynthesize at temperatures only up to 25°C. The rETRmax at 25°C, ranged from 39.18 ± 3.42 (500 μmol photons m−2 s−1) to 22.83 ± 1.05 (0 μmol photons m−2 s−1), which was lower than the values recorded at an equivalent irradiance in in-situ summer. However, if ambient temperature exceeds 25°C in summer, it is likely that the photosynthetic capabilities of the MPB will be diminished and it will cause irreversible photoinhibition.

Section: Discussionmentioning

confidence: 95%

Combined effects of high temperature and light on the photosynthetic parameters and recovery of temperate microphytobenthos in Browns River, Tasmania

Salleh

2022

J. Mar. Biol. Ass.

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“…Furthermore, some of the variation could also have been caused by the fluorescence method itself and the duration of RLC exposure. For example, Lefebvre et al (2011) noted that α was systematically lower due to the slower relaxation of NPQ in 10 s RLCs.…”

Section: Effects Of Irradiance and Temperature Incubationsmentioning

confidence: 99%

“…The extent of photooxidative damage and the speed of recovery are related to the degradation rate of the D1 protein and the subsequent re-synthesis and replacement by new proteins (Derks and Bruce, 2018;Domingues et al, 2012). Similarly, benthic diatoms inhabiting sediment surfaces in estuaries are usually able to recover from extreme temperatures and light photoinhibition caused by tidal changes, since photoinhibition is only rarely recorded in these communities (Defew et al, 2004;Lee and McMinn, 2013;Perkins et al, 2006). Furthermore, many have the ability to migrate vertically, hence positioning themselves within the sediment at a depth that provides shading from excess irradiance and provides an optimal light environment for their photosynthetic activities (Cartaxana et al, 2011;Mouget et al, 2008;Perkins et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Tolerance of tropical marine microphytobenthos exposed to elevated irradiance and temperature

Salleh

2021

Biogeosciences

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Abstract. The photosynthetic productivity of tropical microphytobenthos (MPB) is largely driven by changes in light intensities and temperature at the surface of sediment flats during emersion. Here, the response of the MPB community to temperature and light was examined. Changes in temperature and irradiance during tidal cycles in the Tanjung Rhu estuary, Langkawi, Malaysia, in 2007 significantly affected the photosynthetic capacities of the MPB. Higher photosynthetic parameters, such as the maximum relative electron transport rate (rETRmax), photosynthetic efficiency (α), maximum quantum yield (Fv/Fm), and effective quantum yield (ΔF/Fm′), were recorded at high tide when the temperatures were lower. However, when the community was experimentally exposed to irradiances of 1800 µmol photons m−2 s−1, it was only able to photosynthesize at temperatures < 50 ∘C. Above this temperature, no photosynthetic activity was observed. Not only did high temperatures at high irradiance affect the algal communities, but limited photosynthetic activity was also observed in samples when exposed to limited irradiance. Recovery rates were highest at the lowest temperatures and decreased as the temperature increased. The recovery rates for samples exposed to temperatures of 40 ∘C were 4.01×10-3±0.002 s−1 and decreased to 1.01×10-5±0.001 s−1 at 60 ∘C, indicating irreversible damage to Photosystem II (PSII). These characteristics suggest that the MPB communities in this estuary were able to adapt to temperature variation. However, enhanced photoinhibition would result if exposed to elevated temperatures, especially during low tide where in situ temperature was already 43 ∘C. Hence, if in situ temperature were to further increase during tidal emersion, 50 ∘C could be a temperature threshold for photosynthetic performance of tropical estuarine benthic microalgal communities.

“…We have previously examined the photophysiological response of MPB in Tasmanian coastal ecosystems to elevated light levels (Jordan and McMinn , Jordan et al. ) and extreme temperatures (Lee and McMinn ). Cook et al.…”

mentioning

confidence: 99%

“…We have previously examined the photophysiological response of MPB in Tasmanian coastal ecosystems to elevated light levels McMinn 2008, Jordan et al 2010) and extreme temperatures (Lee and McMinn 2013). Cook et al (2004) examined carbon and nitrogen cycling in a nearby mudflat and concluded that a significant proportion of the production was exported as DOC and EPS rather than cellular production.…”

mentioning

confidence: 99%

Use of glucose biosensors to measure extracellular glucose exudation by intertidal microphytobenthos in southern Tasmania

Lee

2018

Journal of Phycology

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Micro glucose biosensors were used to measure net extracellular glucose produced by natural microphytobenthos and three diatom cultures (Amphora coffeaeformis, Navicula menisculus, Nitzschia longissima) from southern Tasmania, Australia. They were exposed to a light gradient in either nutrient-replete or nutrient-limiting conditions. Glucose exudation in the natural communities increased with increased light but the response in the cultures was variable. Similarly, nutrient-replete conditions elicited lower rates of glucose exudation in the natural communities but produced variable species-specific responses in the cultures. Increased glucose exudation mostly correlated with a reduction in maximum quantum yield (F /F ). The same trend was observed in the natural communities for relative maximum electron transfer rates (rETR ) but responses in the cultures were again variable and species-specific. Responses of the three species to increased light and nutrient deficiency were variable, although glucose exudation, F /F and rETR was mostly lower in the nutrient-limited media. In a second set of experiments species/communities were treated with/without antibiotics. In the dark, glucose concentrations in treatments with antibiotics remained unchanged, while in those with bacteria, it fell rapidly. In the sediment communities, glucose consumption in the dark was ~25% the rate of exudation at the highest light level. In culture, exudation rates were up to 100% greater than those with active bacteria. Rates of glucose consumption in the dark in the antibiotic-treated samples were negligible and up to 10 times lower than those with active bacteria. These results demonstrate the important role extracellular glucose exudation has on maintaining an active microbial loop.