3.4 Photosynthetic performance of macroalgae irradiated with variable UVR
3.4.2 High PAR and variable UVR
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Comparatively, α was reduced by more than 78% in S. chordalis and by more than 44% in L. digitata after irradiation with PAR+UVR at L3 (Fig. 41Ci). A distinctive effect between the two PAR+UVR treatments was observed in U. lactuca whereby PAR+UVA+UVB caused more reduction in α (i.e. 69%
reduction) than PAR+UVA (i.e. 56% reduction). In U. lactuca, α was slightly increased by PAR alone.
PAR+UVA+UVB showed a faster recovery of α in U. lactuca (i.e. increased to 89%) than PAR+UVA (i.e. increased to 74%) while PAR-affected algae did not show any recovery (Fig. 41Cii). The α in PAR+UVR-affected S. chordalis and L. digitata recovered to values higher than 55% and 85%, respectively.
After irradiation with PAR+UVR treatments, Ik of the algae increased to more than 35% in S. chordalis and to more than doubled their control values in L. digitata (Fig. 41Di). In U. lactuca, PAR+UVA+UVB caused a higher increase in Ik (i.e. 73% increase) than PAR+UVA (i.e. 34% increase). All affected algae showed signs of recovery with Ik in U. lactuca was fully recovered while a delay in recovery was observed in S. chordalis and L. digitata (Fig. 41Dii).
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The photosynthetic parameters of the macroalgae before irradiation (i.e. pre-irradiation or control) are listed in Table 22. As for L2/L3, the measurements for post-irradiation and post-recovery algae are standardized to 100% of these values.
Table 21: Irradiances of the different spectral ranges in the sun simulator experimental setups.
Setup Species PAR
(µmol m-2 s-1)
PAR (W m-2)
UVA (W m-2)
UVB (W m-2)
Ratio of PAR:UVA:UVB
H2 S. chordalis 476 100 7.0 0.42 100:7:0.4
P. palmata 498 105 6.6 0.38 100:6:0.4
L. digitata 496 104 7.0 0.41 100:7:0.4
D. dichotoma 540 114 10.0 0.59 100:9:0.5
U. lactuca 501 105 13.4 0.68 100:13:0.6
H3 S. chordalis 489 103 19.2 0.22 100:19:0.2
P. palmata 475 100 17.1 0.19 100:17:0.2
L. digitata 496 104 19.0 0.22 100:18:0.2
D. dichotoma 522 110 20.8 0.29 100:19:0.3
U. lactuca 512 108 20.0 0.25 100:19:0.2
Table 22: The maximal quantum yield (Fv/Fm) and photosynthetic parameters determined from rETR vs. actinic light curve in the macroalgae before irradiation at high PAR and variable UVR (i.e. pre-irradiation or control). Data are
means ±SD values of n=12.
Species
Photosynthetic parameters Fv/Fm
[rel. units]
rETRmax [rel. units]
α [rel. units]
Ik [µmol m-2 s-1]
S. chordalis 0.583 ± 0.02 45.16 ± 7.0 0.426 ± 0.03 106.55 ± 18.5
P. palmata 0.482 ± 0.04 11.36 ± 2.4 0.407 ± 0.06 28.52 ± 6.8
L. digitata 0.744 ± 0.02 62.77 ± 5.0 0.516 ± 0.06 124.59 ± 17.6
D. dichotoma 0.687 ± 0.02 48.39 ± 4.2 0.466 ± 0.05 106.69 ± 18.9
U. lactuca 0.736 ± 0.02 35.38 ± 7.8 0.574 ± 0.04 69.78 ± 7.8
At H2, UVA+UVB caused the least reduction of Fv/Fm in all the algal species examined with a 25%
reduction in S. chordalis, 37% in P. palmata, 22% in L. digitata, 18% in D. dichotoma and 35% in U.
lactuca (Fig. 42Ai). Following UVA+UVB was PAR alone with 58% reduction in S. chordalis, 60% in P.
palmata, 76% in L. digitata and 68% in U. lactuca. In D. dichotoma, however, similar trend was observed but was not significant. The highest Fv/Fm reduction was observed with PAR+UVR treatments.
PAR+UVA+UVB caused a significantly higher reduction in P. palmata (i.e. 81%) than PAR+UVA (i.e.
78%) while PAR+UVA caused a significantly higher reduction in D. dichotoma (i.e. 79%) and U. lactuca (i.e. 80%) than PAR+UVA+UVB (i.e. 73% and 76%, respectively). Fv/Fm of all affected D. dichotoma
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and U. lactuca showed a full or nearly a full recovery (Fig. 42Aii). There was a delay in the recovery with PAR+UVR-affected S. chordalis, P. palmata and L. digitata, especially in P. palmata where Fv/Fm in PAR+UVA+UVB increased to a lower 47% compared to the other light treatments. In general, Fv/Fm
recovery was fast in UVA+UVB especially in P. palmata which increased to a significant 88%, followed by PAR alone.
Similar to Fv/Fm, UVA+UVB caused the least effect on rETRmax with a 25% reduction in S. chordalis, 30% reduction in P. palmata, 3% reduction in L. digitata and 33% reduction in U. lactuca (Fig. 42Bi).
However, there was a 12% increase in D. dichotoma after irradiation with UVA+UVB. PAR alone caused the next least effect with a 57% reduction in S. chordalis, 51% reduction in P. palmata, 60% reduction in L. digitata and 58% reduction in U. lactuca. In D. dichotoma, this effect was not significant. The strongest effect was caused by the PAR+UVR treatments. In S. chordalis, rETRmax was reduced by 71%
under PAR+UVA+UVB and a higher reduction was observed under PAR+UVA (i.e. 78%). The opposite effect was observed in P. palmata with an 83% reduction under PAR+UVA+UVB and a 73% reduction under PAR+UVA. In the other species, PAR+UVA caused the highest reduction. There was a slower recovery of rETRmax in PAR+UVA-affected S. chordalis and D. dichotoma (i.e. increased to 65% and 75%, respectively) than the other light treatments which increased to values higher than 75% and 85%, respectively (Fig. 42Bii). In contrast, PAR+UVA+UVB-affected P. palmata showed the slowest recovery with an increase to 36% compared to more than 55% in other light treatments. Furthermore, rETRmax of L.
digitata was increased to values higher than their pre-irradiations with an increase to 149% in PAR, and, to 120% in both PAR+UVA+UVB and UVA+UVB but was 8% lower than the pre-irradiations in PAR+UVA.
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Fig. 42: Maximum quantum yield (Fv/Fm, A), maximum relative electron transport rate (rETRmax, B), photosynthetic efficiency (α, C) and light saturation parameter (Ik, D) of S. chordalis, P. palmata, L. digitata, D. dichotoma and U.
lactuca after 5 h irradiation at 476-540 µmol m-2 s-1 PAR, 6.6-13.4 Wm-2 UVA and 0.4-0.7 Wm-2 UVB (H2, post-irradiation, i) and after 18 h recovery under dim light (post-recovery, ii). Black bars: PAR, dark grey bars:
PAR+UVA, light grey bars: PAR+UVA+UVB, white bars: UVA+UVB. Data are means ±SD values. Different letters above bars indicate significant difference between different light treatments within similar species (ANOVA,
Fischer’s LSD test, p < 0.05, n=3).
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The trend in Fv/Fm and rETRmax changes was displayed by α as well (Fig. 42Ci). UVA+UVB reduced α of S. chordalis by 43%, P. palmata by 58%, L. digitata by 13% and U. lactuca by 37% but appeared not to affect D. dichotoma. In addition, PAR alone caused a 64% reduction in S. chordalis, 74% reduction in P.
palmata, 76% reduction in L. digitata and 61% reduction in U. lactuca. PAR+UVA+UVB caused the strongest effect in P. palmata with a 91% reduction while PAR+UVA caused the strongest effect in S.
chordalis and U. lactuca with an 85% reduction in both algal species. In D. dichotoma, it appeared that PAR+UVA caused the strongest effect, followed by PAR and PAR+UVA+UVB. A delay in α recovery was observed in PAR+UVA-affected S. chordalis which increased to 55% compared to more than 65% in other light treatments (Fig. 42Cii). On the other hand, PAR+UVA+UVB-affected P. palmata showed a delay in recovery (i.e. increased to 29%) compared to PAR+UVA (i.e. increased to 39%). In U. lactuca, UVA+UVB showed the fastest recovery (i.e. increased to 93%), followed by PAR (i.e. increased to 79%) and PAR+UVR treatments. All affected D. dichotoma and PAR-affected L. digitata showed nearly a full recovery while recovery in PAR+UVR- and UVA+UVB-affected L. digitata was delayed.
Contrastingly, PAR+UVR treatments caused a 50% increase in Ik of S. chordalis while PAR alone caused the least effect, followed by UVA+UVB (Fig. 42Di). Ik was increased between 68% and 90% and between 11% and 28% in post-irradiation P. palmata and D. dichotoma, respectively. UVA+UVB caused the least increase in L. digitata with 12% while in the rest of the light treatments, Ik increased by more than 65%. In addition, whilst Ik was increased the least by UVA+UVB in U. lactuca with only 6%, in the rest of the light treatments, Ik was increased by about 50%. All post-recovery algae showed signs of recovery except for L. digitata under PAR+UVA+UVB (Fig. 42Dii). A delay in Ik recovery was observed in PAR-affected P. palmata (i.e. reduced to 106%), PAR+UVA-affected L. digitata (i.e. reduced to 128%) and UVA+UVB-affected U. lactuca (i.e. reduced to 96%). Furthermore, Ik in PAR+UVR-affected D. dichotoma was reduced to ca. 85% after the recovery period.
Interestingly, most of the algae showed a higher reduction of Fv/Fm at H3 (Fig. 43Ai) than H2 (Fig. 42Ai) after post-irradiation treatment with additional UV. This was noticeable with S. chordalis (p=0.019), D.
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dichotoma (p=0.040) and U. lactuca (p<0.001). In contrast, L. digitata showed a higher reduction at H2
than H3 (p=0.045) while a similar trend was also observed with P. palmata but with insignificant difference (p=0.310). When compared with H1 (Fig. 16Ai), reduction was higher at H1 than H3 in S.
chordalis (p<0.001) and D. dichotoma (p=0.003) but was lower at H1 than H3 in U. lactuca (p=0.001).
Furthermore, H1 caused higher reduction than H2 for L. digitata (p<0.001) and P. palmata (p=0.001).
Similar to H2, the least effect was still caused by UVA+UVB at H3 but with a 40% reduction in S.
chordalis, 29% reduction in L. digitata, 32% in D. dichotoma and 45% in U. lactuca. The next least effect was observed with PAR alone with a 69% reduction in S. chordalis, 72% in L. digitata, 73% in D dichotoma and 77% in U. lactuca. PAR+UVR treatments caused the strongest effect on Fv/Fm of the algae. The effect was stronger under PAR+UVA in S. chordalis (i.e. 83% reduction) and U. lactuca (i.e.
96% reduction) than under PAR+UVA+UVB (i.e. 77% and 92% reductions, respectively) while PAR+UVA+UVB was stronger in D. dichotoma (i.e. 83% reduction) than under PAR+UVA (i.e. 77%
reduction). Fv/Fm recovery was faster at H3 than H2 in S. chordalis (p<0.001), P. palmata (p=0.468) and U. lactuca (p=0.993) while H2 showed faster recovery than H3 in L. digitata (p=0.049) and D. dichotoma (p<0.001). In addition, PAR+UVA+UVB had the slowest Fv/Fm recovery in S. chordalis which increased to 43% while PAR+UVA was the slowest in U. lactuca which increased to 72%. UVA+UVB was the fastest to recover which increased to 82% in S. chordalis, 95% in P. palmata, 90% in L. digitata, 97% in D. dichotoma and 98% in U. lactuca. The next to recover following UVA+UVB was PAR alone which increased to 72% in S. chordalis, 79% in both P. palmata and L. digitata, and 92% in D. dichotoma.
However, PAR+UVA+UVB was the next to recover in U. lactuca which increased to 92%.
The rETRmax of L. digitata was increased by 9% when irradiated with UVA+UVB at H3 (Fig. 43Bi). In D.
dichotoma, UVA+UVB caused no effect on rETRmax but a 38% reduction in S. chordalis and 23%
reduction in U. lactuca. In S. chordalis, the highest reduction was observed under PAR+UVA with 84%.
It appeared that PAR+UVA caused the highest reduction in P. palmata and L. digitata as well but the highest reduction in D. dichotoma and U. lactuca was under PAR+UVA+UVB. In addition, PAR alone caused a 76% reduction in U. lactuca, the least affected after UVA+UVB. All affected P. palmata
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Fig. 43: Maximum quantum yield (Fv/Fm, A), maximum relative electron transport rate (rETRmax, B), photosynthetic efficiency (α, C) and light saturation parameter (Ik, D) of S. chordalis, P. palmata, L. digitata, D. dichotoma and U.
lactuca after 5 h irradiation at 475-522 µmol m-2 s-1 PAR, 17.0-20.8 Wm-2 UVA and 0.2-0.3 Wm-2 UVB (H3, post-irradiation, I) and after 18 h recovery under dim light (post-recovery, II), details as in Fig. 42.
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showed an increase of rETRmax to values higher than 60% after the recovery period (Fig. 43Bii). In S.
chordalis, PAR+UVR showed a slower recovery than PAR and UVA+UVB. In D. dichotoma, all light treatments showed a tendency to a full rETRmax recovery except in PAR+UVA+UVB. Whilst UVA+UVB showed a full recovery in U. lactuca, other light treatments showed a delay in recovery. Contrastingly, rETRmax of L. digitata increased to values exceeding that of their pre-irradiations especially with PAR+UVA+UVB which increased to 150%.
UVA+UVB caused the least effect on α of the algae as well (Fig. 43Ci). There was a 60% reduction in S.
chordalis, 5% reduction in L. digitata, 9% reduction in D. dichotoma and 53% reduction in U. lactuca after irradiation with UVA+UVB. In S. chordalis, α was the strongest affected by PAR+UVA with a 91%
reduction, followed by PAR and PAR+UVA+UVB. P. palmata showed the strongest effect with PAR+UVR treatments, followed by PAR and UVA+UVB. In U. lactuca, the strongest effect was observed with PAR+UVR treatments as well, followed significantly by PAR with an 82% reduction.
Furthermore, a trend was observed in the brown algae L. digitata and D. dichotoma whereby PAR+UVA showed the strongest effect on α, followed by other light treatments. Recovery of α was the fastest with UVA+UVB especially in S. chordalis, P. palmata and U. lactuca which increased to 75%, 55% and 83%, respectively (Fig. 43Cii). In general, recovery was the slowest with PAR+UVR treatments followed by PAR while most of affected L. digitata and D. dichotoma had their α fully or nearly fully recovered.
Ik of S. chordalis increased by more than 50% after irradiation with all light treatments with the least under UVA+UVB, followed by PAR+UVA+UVB, PAR and PAR+UVA (Fig. 43Di). In P. palmata, PAR+UVA+UVB caused the highest increase with 90%, followed by PAR+UVA, PAR and UVA+UVB.
UVA+UVB caused the least increase in L. digitata and D. dichotoma with 14% and 10%, respectively, followed by PAR+UVR and PAR in L. digitata and the opposite in D. dichotoma. In addition, PAR caused the least increase in Ik of U. lactuca followed by PAR+UVR and UVA+UVB. The slowest recovery of Ik in S. chordalis appeared to be in PAR while in the rest of light treatments, full recovery
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was attained (Fig. 43Dii). In P. palmata, Ik recovered the fastest under UVA+UVB which was reduced to 114% and the slowest was observed under PAR+UVA+UVB which was reduced to 171%. There appeared to be a delay in recovery under PAR+UVA but a faster recovery under PAR compared to the other light treatments in U. lactuca. All affected D. dichotoma either fully recovered or nearly fully recovered. Contrastingly, Ik of PAR+UVA+UVB-affected L. digitata showed an increasing trend after the recovery period. However, when compared with the post-irradiation algae, there was no significant difference. In addition, PAR was the fastest to recover in L. digitata, followed by PAR+UVA and UVA+UVB.
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