Tải bản đầy đủ - 0 (trang)
 Impact on Macroalgae Photosynthesis

 Impact on Macroalgae Photosynthesis

Tải bản đầy đủ - 0trang

204



E. WALTER HELBLING ET AL.



PAR (J m−2)



1.6x107

1.2x10



a



7



8.0x106

4.0x106

0.0x100



UVA (J m−2)



2.0x106

1.6x10



b



6



1.2x106

8.0x105

4.0x105

0.0x100



UVB (J m−2)



6.0x104



c



4.0x104

2.0x104

0.0x100



Ozone (D.U.)



440

400



d



360

320

280

240

200



1/1999 1/2000 1/2001 1/2002 1/2003 1/2004 1/2005 1/2006 1/2007

Figure 1. Daily doses of solar radiation and ozone concentration in the area of Bahía Engo from

1999 to 2007. (a) PAR (400–700 nm); (b) UV-A (315–400 nm); (c) UV-B (280–315 nm); (d) Ozone concentrations (in D.U.). Solar radiation data were obtained with a broadband ELDONET radiometer

(www.eldonet.org) permanently installed on the roof of Estación de Fotobiología Playa Unión. Ozone

concentrations data were obtained from NASA (http://jwocky.gsfc.nasa.gov). Note the low ozone values during springtime (inside ovals).



ULTRAVIOLET RADIATION EFFECTS ON MACROALGAE



205



throughout the upper eulittoral to the supralittoral zone in shallow rock pools.

Using a pulse amplitude modulated fluorometer (PAM, 2000, Walz, Effeltrich,

Germany), it was found that the nonphotochemical quenching (qN) rises with

increasing irradiances of actinic light starting as low as 10 W m−2, whereas the

photochemical quenching (qP) decreases antagonistically (Häder et al., 2000).

This physiological response has also been found in higher plants (Niyogy et al.,

1998). When exposed to solar radiation for 15 min during low tide and at solar

noon on a bright day, the photosynthetic yield (Y) decreased to about 50% of its

value in dark-adapted plants, but recovered rapidly within 30 min in dim light.

When solar UV-B radiation was excluded using filter foils (Montagefolie, Folex,

Dreieich, Germany), Y was significantly less impaired.

The Chlorophyte Enteromorpha linza occurs in the same habitat, but during

low tide, it is exposed on the rocky surface as it rarely grows inside the rock pools.

When exposed to solar radiation for 15 min during low tide and at solar noon, the

decrease in Y is even more pronounced than in U. rigida and decreases to ~0.2

from the initial dark-adapted value of 0.7 (Häder et al., 2001a). Cutting off the

UV-B wavelength band resulted in a less pronounced reduction in Y and cutting

off the total UV band (using Ultraphan UV Opak filter, Digefra, Munich,

Germany) caused an even less pronounced inhibition. The effects of the UV-B or

total UV components of solar radiation were still visible throughout the recovery

period in dim light. In the experiments described here, the thalli were confined to

a flow-through holder and constantly exposed to solar radiation. However, when

exposed free floating in a mesocosm, there was a decrease in Y by only ~35% during clear days and less pronounced on cloudy days; but in any case, the effects of

especially the UV-B band were noticeable.

The filamentous Rhodophytes Ceramium sp. and Callithamnion gaudichaudii

were found in the lower eulittoral inside rock pools. Both were strongly affected

by solar radiation (Häder et al., 2004). Both UV-A and UV-B had pronounced

effects compared with that of PAR (Fig. 2). Recovery was much slower than in

the Chlorophytes and the Y was back to the dark-adapted value only during the

night. However, it is interesting to note that the increase in qN and the decrease

in qP started at much higher irradiances than in the Chlorophytes (about 50 W m−2).

Similar results were found in the Rhodophyte Porphyra columbina, which grew on

the shaded sides of the rock pools in the lower eulittoral.

Two growth forms of Corallina officinalis were found in the middle and low

eulittoral (only accessible during very low tides), which differed in their morphology and calcification so that the skeleton of the low-eulittoral Corallina was less

calcified than that in the mid-eulittoral algae (45% (w/w) and 49% of the total dry

weight (DW), respectively (Richter et al., 2006)). Moreover, it was found that their

photosynthetic parameters were different as well (Häder et al., 2003). The induction curves with quenching analysis showed a faster decrease in the current and

maximal fluorescence (Ft and Fm) in the low eulittoral strain compared with the

mid eulittoral growth form. Simultaneously, qN rose much faster and higher in

the low eulittoral strain (Fig. 3).



206



E. WALTER HELBLING ET AL.

0.6



Photosynthetic yield



0.5

**



0.4



**



***



**



17:45



20:45



*



*



**



0.3

0.2

0.1

0

Dark



15 min

14:45

exposure



15:45



00:45



06:45



Control



Local time [h]



Figure 2. Effective photosynthetic quantum yield in Ceramium sp. measured after 30 min dark adaptation,

15 min exposure, and after increasing recovery times in the shade. Gray bars, specimens exposed to

unfiltered solar radiation. Black bars, specimens exposed to UV-A and PAR. Open bars, specimens

exposed to PAR only. (After Häder et al., 2004.)



The Phaeophyte Dictyota dichotoma was found in rock pools in the mid

eulittoral. After exposure to 15 min of solar radiation in a fixed position, the

effective Y decreased dramatically and did not fully recover until the next morning (Häder et al., 2001b). Free floating thalli were not affected as much as those

in a fixed position.

Overall, there is a wide range of photosynthetic responses of Patagonian

macroalgae to solar radiation. All results from Patagonia and other coasts confirm

that the sensitivity to solar radiation increases with their depth of growth (Häder,

1997). It can be discussed whether this is due to the fact that more sensitive species

select a habitat lower in the water column or whether resistance increased with

higher exposure to solar radiation. In any case, macroalgae have developed a

number of protective mechanisms against excessive solar radiation. In addition to

UV-absorbing compounds (see Section 5), most macroalgae use an effective repair

mechanism for damaged DNA and proteins in the photosynthetic apparatus. To

prove that the D1 protein in the reaction center of photosystem II is resynthesized

after photodamage and proteolysis, streptomycin or chloramphenicol were

applied during recovery of several macroalgae (Ulva, Porphyra, Dictyota). Both

delayed the recovery indicating that the D1 protein resynthesis was inhibited

(Häder et al., 2002). Several macroalgae groups use the xanthophyll cycle to dispose of excessive radiation by thermal dissipation (Niyogi et al., 1998).

Dithiothreitol is an inhibitor of the violaxanthin de-epoxidase, so when administered to the same algae it affected both photoinhibition and recovery (Häder

et al., 2002). However, this was also found in the red algae, which are believed not



207



ULTRAVIOLET RADIATION EFFECTS ON MACROALGAE



Fluorescence parameters [a.u.]



a



0.7

0.6



Fluorescence parameters [a.u.]



Fm

Ft



0.4

0.3

0.2



qP



0.1

0.0



b



qN



0.5



Y



0



50



100



150

Time [s]



200



250



300



0.9

0.8



qN



0.7

0.6

0.5

0.4



Fm

Ft



0.3

0.2



qP



0.1

0.0



Y



0



50



100



150



200



250



300



Time [s]

Figure 3. Induction curve with quenching analysis in the mid-eulittoral strain (a) and the low eulittoral

strain (b) of Corallina officinalis. (After Häder et al., 2003.)



to possess the xanthophyll cycle. This indicates that the inhibitor should be used

with caution since it seems to have strong side effects.

5. Presence and Dynamics of UVR-Absorbing Compounds

in Patagonian Macroalgae

Macroalgae constitute a source of UV-absorbing compounds, typically mycosporinelike amino acids (MAAs). These compounds are known to protect organisms

against UVR stress because of their ability to absorb short wavelengths, but

other ecophysiological functions such as protectors against desiccation or as

osmotic regulators, antioxidants, and even as accessory pigments have been

reported (Korbee Peinado et al., 2006). Therefore, the capacity of synthesizing

and accumulating these compounds would provide an adaptive advantage for

organisms exposed to different ambient stressors. This is especially important



208



E. WALTER HELBLING ET AL.



for Patagonian macroalgae that are subjected to high radiation levels and suffer

desiccation, especially during low tides and at summer time. Studies dealing with

these compounds in Patagonian macroalgae have focused on two main aspects:

(a) to determine their presence and abundance in key species of the community

and (b) to assess their dynamics throughout daily cycles and considering the tide

effects. These studies are particularly important in the context of climate change,

as they give insight into the capacity of different algae to cope with increasing

solar radiation.

Specific studies were carried out with the two strains of the Rhodophyte

Corallina officinalis (i.e., low- and mid-eulittoral forms). High-performance liquid

chromatography (HPLC) analysis indicated the presence of two MAAs, shinorine

and palythine, with the absolute concentration of the latter being about tenfold

higher than that of the former (Fig. 4). The amount of MAAs in low-eulittoral

samples was significantly lower than that in the mid-eulittoral strain. Significant

diurnal changes in the MAAs concentration and in the ratio between shinorine

and palythine of the low-eulittoral Corallina algae were also observed (Richter

et al., 2006): Both MAAs concentration increased around local noon, but the

ratio between shinorine and palythine decreased during midday owing to a higher

increase in palythine over shinorine (Fig. 4). In the afternoon, the MAAs concentration decreased again. In the mid-eulittoral strain, MAAs dynamics showed an

opposite pattern so that around noon the palythine concentration decreased compared with shinorine, whereas in the afternoon the palythine concentration

tended to increase. Although the data indicate a strong influence of solar radiation on MAAs synthesis in C. officinalis, it is still an open question, whether

endogenous circadian or circatidal rhythms are also involved in this process.

Concentration of UV-absorbing compounds and photosynthetic pigments as a function of different radiation treatments throughout daily cycles

were done with the Rhodophyte Porphyra columbina. Five MAAs were identified: mycosporine–glycine, shinorine, porphyra-334, palythine, and asterina.

Porphyra-334 was the most abundant MAA (~80% of the total concentration)

and it was always present regardless of the conditions under which the algae

were exposed. Shinorine was also present in high concentrations (~20%),

whereas the remaining MAAs occurred at much lower concentrations.

UV-absorbing compounds in P. columbina generally decreased throughout the

daily cycles in the two radiation treatments implemented (i.e., PAR+UVR and

PAR only) but, in contrast to Corallina officinalis, higher values were determined at night; also, and in general, slightly lower values at the end of the

experiment were determined in samples exposed only to PAR. The concentration of photosynthetic pigments, on the other hand, remained low throughout

the experiment. Results from ammonium-enrichment experiments on the synthesis of MAAs and photosynthetic pigments (Korbee Peinado et al., 2004)

showed no significant increase in the concentration of MAAs during a 6-day

exposure at concentrations of 0 and 50 mM NH4+. On the other hand, samples



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

 Impact on Macroalgae Photosynthesis

Tải bản đầy đủ ngay(0 tr)

×