RESEARCH ARTICLE

I. Gomez Æ N. Ulloa Æ M. Orostegui

Morpho-functional patterns of photosynthesis and UV sensitivityin the kelp Lessonia nigrescens (Laminariales, Phaeophyta)

Received: 28 January 2005 / Accepted: 23 May 2005 / Published online: 28 September 2005� Springer-Verlag 2005

Abstract The photosynthetic responses of the southPacific kelp Lessonia nigrescens of the coast of Valdivia,Chile (40�S), were investigated by exposing its differentthallus parts, fronds, stipes and holdfasts, to UV radi-ation in the laboratory. Biologically effective doses(BEDphotoinhibition300) between 400 and 800 kJ m�2 wererequired for a 40% inhibition in photosynthesis underUVA+UVB radiation. At BEDphotoinhibition300 close to250 kJ m�2 (in treatments without UVB), the inhibi-tion of photosynthesis did not exceed 20%. These UVdoses were in the range of current daily doses measuredin Valdivia on cloudless summer days. In general,exposure to UVB for periods longer than 12 h reducedphotosynthesis, measured as maximal quantum yield(Fv/Fm) and electron transport. The fronds were themost UV-sensitive section of this alga, coinciding withthe highest pigments contents and carbon fixation.Evidence of a photodamage was also seen. After a 48 hexposure to PAR+UVA+UVB, a decrease of Fv/Fm inthe fronds was close to 41%, while in the stipes andholdfasts it was 12 and 18%, respectively. Although thethalli from the different size classes showed markeddifferences in their morphology and morphometry, noobvious differences in the UV tolerance of the frondswere detected. The results indicated that the UV-relatedresponses are integrated in the suite of morpho-func-tional adaptations of the alga. Although the fronds arespatially more exposed to solar radiation than basalstructures (stipes and holdfast), due their high turnoverrate they may compensate better detrimental effects ofUV. In contrast, stipes and the holdfast are key supportstructures characterized by low replacement rates and

designed to confer hydrodynamic resistance to dragforces.

Introduction

Kelps attain a complex morphology, and consequentlyan intrinsic differentiation of metabolic processes alongthe thallus can be distinguished (Luning et al. 1973;Kuppers and Kremer 1978). Such a morpho-functionalorganization has also been reported in some Fucales(Kuppers and Kremer 1978) as well in species of theAntarctic genera Desmarestiales and Ascoseirales (Drewand Hasting 1992; Gomez et al. 1996). The occurrence ofgradients in photosynthesis rates, synthesis and accu-mulation of reserve carbohydrates and biomass alloca-tion, which are determined by the localization of carbonassimilatory and ‘‘sink’’ regions, have been reported(Kremer 1981). In species of the order Laminariales, theapical zone is the photosynthesis specialized part ofthallus, while the meristematic growth zone is located inthe basal region of the lamina. Under dim light ordarkness, the action of the meristem can be powered byreserved carbohydrates translocated from the apicalzones (Kremer 1984; Schaffelke 1995; Cabello-Pasiniand Alberte 2001). In general, light is regarded as themajor environmental factor regulating the expression ofsuch processes, which link photosynthesis and growth.Critical levels of irradiance and/or daylengths, normallyduring winter or winter/spring season, trigger the startof the new blade growth, which normally require the useof storage carbohydrates synthesized in the previousspring-summer season (Kremer 1981; Gomez and Lun-ing 2001).

Taking into account that the thallus architecture ofthe kelp Lessonia nigrescens (Bory; Laminariales, Les-soniaceae) implies differences in the morpho-functionaldesign among its structural parts and consequently dif-ferent rhythms of development due to the action of thebasal meristem, gradients of sensitivity to solar radiation

Communicated by O. Kinne, Oldendorf/Luhe

I. Gomez (&) Æ N. Ulloa Æ M. OrosteguiInstituto de Biologıa Marina, Universidad Austral de Chile,Casilla 567, Valdivia, ChileE-mail: igomezo@uach.clTel.: +56-63-221210Fax: +56-63-221455

Marine Biology (2005) 148: 231–240DOI 10.1007/s00227-005-0043-0

may intuitively be expected. For example, the questionwhether younger thallus parts are more sensitive to UVradiation than older ones has not often been addressed.However, it is necessary to look at the intra-thallusdifferences in UV tolerance in order to further evaluatethe response of the whole plant. These changes could beassessed using quenching analysis, in particular, chlo-rophyll fluorescence of PSII (photosystem II), whichgives insights into the short-term photochemical reac-tions, hence the photobiological performances of thethallus regions. This should be the first step in order tofurther examine other photosynthetic responses such ascarbon assimilation and allocation as well as theirimplications for primary productivity of coastal systems,where the Laminariales account for a great fraction ofthe whole algal biomass.

The kelp L. nigrescens is abundant at the rockyshores along the Chilean coast and in virtue of its greatsize and perennial characteristics, it is regarded as a keyorganism at intertidal locations (Santelices 1989).Moreover, L. nigrescens is also being harvested and ex-ported as raw material for alginate extraction (Vasquezand Santelices 1990; Anonymous 2003). The populationdynamics and the reproductive phenology of L. nigres-cens are markedly seasonal and regulated by strongcompetitive interactions with the other large seaweedfrom this region, the southern bull-kelp Durvillaea ant-arctica (Santelices et al. 1980; Westermeier et al. 1994).Although much of the ecological functions and demog-raphy of this species are relatively well known (Sante-lices and Ojeda 1984; Ojeda and Santelices 1984;Westermeier et al. 1994), data on morpho-functionalpatterns and light relations are scarce or not available.Two major aspects require particular attention: (a) anexamination of the photosynthetic acclimation of thisalga to different light conditions, including UV radiationand (b) the assessment of the longitudinal gradients inthe photosynthetic performance of L. nigrescens. Insouthern Chile, algae can currently be exposed to en-hanced solar UVB radiation (280–315 nm), especiallyduring spring–summer (Lovengreen et al. 2000). Re-cently, it was reported that algae inhabiting the infra-littoral zone, with the dominance of L. nigrescens, aremore susceptible to UVB radiation (expressed as a de-crease in photosynthesis) as compared to species grow-ing at upper locations (Gomez et al. 2004). On the otherhand, Westermeier and Gomez (1996) demonstratedthat the major organic constituents and energy alloca-tion in L. nigrescens are strongly linked to their mor-phology, characterized by multiple stipes and a greatnumber of fronds emerging from a single, massiveholdfast. The biomass allocated to the different thallusparts varies allometrically, so that fronds account forapproximately 70% of the allocated biomass in algaewith holdfasts <10 cm, whereas in attaining a holdfastdiameter >20 cm, fronds only represent 25% of thealgal biomass. The existence of sieve elements in thisspecies may also suggest the idea of a remobilization oforganic substances (Nunez and Alveal 1988). Thus in the

present study we examined whether highly differentiatedthallus parts of L. nigrescens exhibit different photo-synthetic performance also, measured as chlorophyllfluorescence, after exposures to UV radiation in thelaboratory.

Material and methods

Algal material and irradiation conditions

Lessonia nigrescens was collected at Playa Rosada,25 km from Valdivia, Chile (39�51¢S, 73�23¢W) at dif-ferent times between September and December (spring-summer) 2003. The algae were transported to the labo-ratory where they were cleaned of epiphytes and dividedin their different parts (fronds, stipes and holdfast).Previously, the diameter of the holdfast, the lengths offronds and stipes as well as the number of stipes wererecorded for each sample. Algae were maintained over-night under constant illumination provided by fluores-cent lamps (70 lmol m�2 s�1, Daylight Phillips) toallow acclimation. In September and previous to theexposure to UV radiation, the physiological character-istics and pigment contents in the different thallus partswere determined according to the methodology de-scribed below. For the experiments of UV susceptibility,three different algae were selected and sample-discs witha diameter of 8 mm were punched from each thallus partusing a cork borer. The sample-discs were incubated inseparate Petri dishes (52 discs in each dish) containing150 ml filtered seawater (0.45 lm, MFS GC50, Japan).A preliminary test indicated no differences in the pho-tosynthetic responses when different disc diameters (4, 8and 10 mm) were used (data not shown). Due to thelimited space, it was not feasible to use replicate Petridishes, but instead experimental series were repeatedthree times during the study period of 3 months. Samplediscs used for experimentation were generally punchedin a way that the cuts of each thallus part includedphotosynthetic cells. Due to the flattened shape of thefronds, these discs corresponded to a whole transversalsection, including epidermis, cortex, and medulla. In themassive stipes and holdfasts, the cut sections includedthe photosynthetic outer layer (epidermis) and somelayers of the cortex. Thus, the sample discs were opti-cally comparable and differences in UV susceptibilityreflect only the intrinsic variability along the thallus. Itmust be emphasized that physiological performance andpigments contents were standardized to weight unit inorder to outline the morphology of L. nigrescens better,which attains a massive leathery thallus anatomy (seebelow in discussion). The Petri dishes were maintainedin a thermoregulated water bath (13–15�C) under vig-orous aeration (Fig. 1) and the seawater was changedevery 12 h. A similar procedure was followed whenfronds from different size-class algae were exposed.

For physiological measurements of chlorophyll fluo-rescence (see below) the thallus discs were incubated

232

under three irradiation conditions using lamps emittingphotosynthetically active radiation (PAR) (DaylightPhillips), as well as UVA (315–400 nm) and UVB (280–315 nm) radiation (Q-panel 340 and Q-Panel 313, USA).In order to set three different UV treatments, the disheswere covered with different cut off filters:

(a) PAR+UVA+UVB = Ultraphan 295 (Digefra,Germany), for exposure to full spectrum

(b) PAR + UVA = Folex 320 (Folex, Germany), tofilter wavelengths <320 nm.

(c) PAR = Ultraphan 395 (Digefra, Germany), whichcut off UV wavelengths.

Incident irradiances under the different combina-tions of lamps and cut off filters are indicated in Ta-ble 1. The spectral characteristics of these lamps andfilters are described by Figueroa et al. (1997). Theexperimental irradiances were weighted using the actionspectrum for photoinhibition of photosynthesis asnormalized to unity at 300 nm (measured from isolatedchloroplasts; Jones and Kok 1966), following the cal-culations described by Gomez et al. (2001). The UVdoses are thus presented as biologically effective doses(BED). The samples were maintained for different timeperiods (2, 6, 12, 24 and 48 h) under these irradiationconditions, which with respect to UVB are in the rangeof cloudless summer days in Valdivia (Lovengreen et al.

2000). At each time interval, sample-discs of algae weretaken out for measurements and analyses. To examinethe capacity of recovery of photosynthesis and the ef-fect of UV radiation, samples were exposed to thedifferent radiation conditions described in Table 1 for12 h and then covered with a light shading screen inorder to reduce PAR by 50% (30 lmol m�2 s�1) andUV by 100%.

Chlorophyll fluorescence measurements

In vivo chlorophyll fluorescence of PSII was measuredusing a computer-aided portable pulse modulationfluorometer (PAM 2000, Walz, Germany). Ten discswere taken from each treatment, incubated for 20 min inthe dark and measured for optimal quantum yield offluorescence (Fv/Fm), which is an indicator of quantumefficiency (Schreiber et al. 1994).

Electron transport rate (ETR) was estimated from thephotosynthesis versus light curves (P�I). Thallus pieces(n=3) were put in a stainless-steel chamber and irradi-ated with increasing intensities of PAR (up to 400 lmolphoton m�2 s�1) provided by a LED lamp of the PAMdevice. ETR was estimated by relating effective quantumyield (FPSII) and the intensity of the radiation (Schreiberet al. 1994):

Table 1 Experimental design indicating irradiances from lamps and UV-cut off filter treatments

Treatment Experimental irradiance (Wm�2) Weighted irradiance (Wm�2)

UVB UVA PARa Inhibition of photosynthesis

PAR+UVA+UVB 2.35 8.57 64.20 4.57PAR+UVA 0.16 5.17 63.30 1.36PAR 0.03 0.78 62.20 0.17

Fig. 1 Schematic drawing (notto scale) of the thermoregulatedsystem used in incubating thesample discs of Lessonianigrescens under different UVconditions. See text for details

Weighted irradiances were calculated using a well know weightingfunction for biological UV responses, the inhibition of photosyn-thesis of isolated spinach chloroplasts (Jones and Kok 1966)

a PAR in lmol m�2 s�1 and was measured with a Licor 250 radi-ometer (Licor, USA)

233

ETR ¼ UPSII � EPAR � A� FII ð1Þ

where E is the irradiance of PAR, A the thallusabsorptance, and FII is the fraction of absorbed quantadirected to PSII, which was estimated by determiningthe fraction of the chlorophyll a associated to PSII andits corresponding light harvesting complex (LHC). Forbrown algae, this value is close to 0.8 (Grzymski et al.1997). The absorptance was measured placing samplediscs (maximum thickness 5 mm) above a Licor 190Squantum sensor connected to a Licor 250 radiometer(LI-COR Biosciences, USA) using natural sunlight(average of ten measurements) according to the tech-nique described by Mercado et al (1996):

A ¼ 1� T � R ð2Þ

where T is the transmittance (light transmitted throughthe sample) and R is the reflectance (reflected fraction).The ETR parameters were calculated fitting a modifiednon-linear function:

ETR ¼ ETRmax � tanhða � E=ETRmaxÞ ð3Þ

where ETRmax is the maximal ETR, tanh is the hyper-bolic tangent function, aETRis initial slope of the P�Icurve and defines the electron transport efficiency at lowirradiance (quantum efficiency), and E is the irradiance.The saturation irradiance for electron transport (Ek) wasalso calculated as the intercept between aETR and theETRmax values. It must be emphasized that ETR wasnormally saturated (Pmax) at irradiances close to400 lmol photon m�2 s�1 (the maximal irradianceprovided by the LED lamp), however, when saturatingpoints exceed the maximal irradiance, maximally mea-sured ETR in the curve was regarded as Pmax.

Pigment analysis and 14C assimilation

The determination of pigments (chlorophyll a, c andcarotenoids) was based on an extraction with N,N-dimethylformamide (DMF) as described by Inskeep andBloom (1985). After an incubation period of 24 h at 4�Cin darkness, the absorptions were measured in a scan-ning SUV-2120 spectrophotometer (SCINCO, Italy).

For the measurement of photosynthetic assimilationof 14C the discs were incubated in a chamber for 30 minat saturating irradiances (250 lmol m�2 s�1) of PARprovided by a halogen lamp. In parallel, samplesmaintained in the dark for 30 min were used for deter-mination of light independent carbon fixation. Thesamples were incubated with 0.7 lCi 14C ml�1 as NaH14

CO3 (Perkin-Elmer Inc., USA). After incubation, sam-ples were rinsed in unlabelled medium and solubilizedwith 0.5 ml 0.5 M NaOH and Triton X-100 (5% v/v) for24 h in darkness. The 14C that was not assimilated byalgae was let to evaporate overnight in a fume hood at50�C after addition of 0.5 ml HCl (1 N). Radioactivitywas measured in a Packard Tri-Carb 460C liquid scin-tillation counter adding 8 ml scintillation cocktail

(Ecoscint). Quenching correction was carried out usingthe external standard channels ratio (ESCR) method.

Statistical treatment

Data were compared by using three-way analysis ofvariance (ANOVA) followed by Tukey HSD post hocanalysis when differences were detected (STATISTICA5.0, Statsoft Inc. USA). As main factors, time of expo-sure, thallus part/size class and UV treatments wereconsidered. Data sets meet criteria for normal distribu-tion and homogeneity of variances which were examinedusing Chi-Square tests and Bartlett, respectively.

Results

Photoinhibition of photosynthesis in fronds

Fronds of L. nigrescens were sensitive to UV wave-lengths as shown in Fig. 2. The course of inhibition ofphotosynthesis followed an exponential curve and atBEDphotoinhibition300 ‡ 300 kJ m�2 Fv/Fm decreased 30–40% in the treatments including UVB. These doses(from 24 h to 48 h exposures) correspond to current UVdoses of cloudless summer days in Valdivia. In thetreatments deprived of UVB, maximal inhibition ofchlorophyll fluorescence reached 20% at BED of250 kJ m�2 . The electron transport rates measured insamples exposed for 24 h were affected by bothPAR+UVA and PAR+UVA+UVB treatments(Fig. 3). At PAR irradiances close to 160 lmol m�2 s�1,ETR decreased by 50% after a 2 h exposure. Similarpattern was observed in samples exposed for 24 h. In

Fig. 2 Inhibition of photosynthesis in the fronds of L. nigrescensmeasured as a decrease (%) of Fv/Fm in relation to an initial controlversus biologically effective doses (Jones and Kok 1966) of UVradiation during 48 h incubations. Data are means ± S.D., n=10measurements

234

general, in the treatments using only PAR, samplesshowed similar photosynthetic responses as the initialcontrols.

Experiments of photoinhibition versus recoveryindicated that photosynthesis of the fronds exposed toPAR+UVA+UVB for 12 h decreased by 45% (averagevalues of Fv/Fm from 0.73 to 0.38), and after 12 h undershaded conditions they did not show any recovery(P<0.05, ANOVA; Tukey HSD, Fig. 4). In contrast,algae deprived of UVB exhibited lower rates of pho-

toinhibition (10–20%), with recovery rates close to 70%(P<0.05, ANOVA; Tukey HSD).

Thallus profiles of physiological performance

The distinct thallus parts of L. nigrescens were charac-terized by different physiological attributes (Table 2).Although the photochemical parameters, Fv/Fm andquantum efficiency (a) did not vary along the thallus,other photosynthetic parameters such as Pmax, irradi-ance for saturation of photosynthesis (Ek) and carbonfixation showed marked differences. In general, electrontransport and carbon fixation rates (both light depen-dent and independent fixation) were significantly higherin apical regions as compared to basal zones. Likewise,fronds had higher amounts of pigments on a weightbasis than basal tissues located at the holdfast (Table 2).

Photosynthesis varied significantly when samplesfrom different thallus parts of L. nigrescens were exposedfor variable times to three treatments of UV radiation(P<0.001, three-way ANOVA; Tukey HSD, Table 3).

Fig. 3 Electron transport rates measured in the fronds of L.nigrescens after 2 and 24 h exposure to three different UVconditions. The initial control is also indicated for comparison.Data are means ± S.D., n=10 measurements

Fig. 4 Photoinhibition and recovery of photosynthesis measured asFv/Fm in the fronds of L. nigrescens exposed to three different UVconditions. Data are mean ± S.D., n=10 measurements. Similarletters connect homogeneous mean groups after Tukey HSD test

Table 2 Physiologicalcharacteristics of L. nigrescensmeasured in different thallusregions. Algae arerepresentative of the holdfastsize-class between 10 cm and20 cm. Data are means ± S.D.,n=10. Similar letters indicateno significant differences amongmeans (P<0.05; Tukey HSD).Details of the differentparameters are given in text

Physiological parameters Thallus part

Fronds Stipes Holdfast

Photosynthetic parametersFv/Fm 0.64±0.02a 0.67±0.04a 0.60±0.02bPmax (lmol e� m�2 s�1) 36.04±9.96a 35.33±1.50a 10.37±1.63ba [(lmol e� m�2 s�1)(lmol m�2 s�1)]�1 0.39±0.03a 0.38±0.10a 0.38±0.10aEk (lmol m�2 s�1) 93.97±31.39a 93.76±21.20a 28.99±12.46bPigments (mg g�1 FW)Chl a 0.28±0.05a 0.19±0.08a 0.08±0.03bChl c 0.04±0.01a 0.03±0.01a 0.01±0.01bTotal carotenoids 0.07±0.01a 0.06±0.03a 0.03±0.01b14C-fixation (lmol14C g�1 FW h�1)fLight carbon fixation 47.49±3.89a 7.17±1.44b 6.42±1.06bb-carboxilation (LIC) 9.61±0.85a 2.34±0.16b 2.72±0.02b

235

The fronds were the most susceptible region of the alga(P<0.05, ANOVA; Tukey HSD). After a 48 h exposureto PAR+UVA+UVB, photosynthesis decreased by41% in relation to the initial control, whereas in algaeincubated under PAR+UVA inhibition of photosyn-thesis was close to 16%. In the case of pieces cut fromstipes and the holdfasts, decreases in photosynthesiswere significantly lower and ranged between 6.5% and21.3% after a 48 h exposure to PAR+UVA+UVB andPAR+UVA. Under PAR alone, inhibition of photo-synthesis relative to the initial control, which did notexceed 10.8%, was also detected, particularly in holdfasttissues, and in general was lower than that recorded inthe treatments including UVB radiation (P<0.05, Tu-key HSD, Table 3).

Photosynthesis in relation to algal size

Photosynthesis varied according to the size also, mea-sured as the holdfast diameter as well as a combinedeffect of the duration of the exposure and the UVtreatment (P<0.001; three-way ANOVA, Fig. 5). Ingeneral, larger algae attaining holdfast with a diameter>20 cm experienced decreases in photosynthesis closeto 33% after a 2 h exposure, whereas in algae with aholdfast diameter of <20 cm, the inhibition of photo-synthesis did not exceed 23%. However, after a 48 h

exposure, the three age/size classes showed similar de-creases in photosynthesis (35–42%). For the three cases,treatments that included UVB had a higher effect onphotosynthesis as compared to PAR+UVA or PAR(P<0.05, ANOVA, Tukey HSD).

When the decrease in photosynthesis (after 48 h)along with the size classes were plotted against theinhibition among thallus parts, it was found that the lastfactor represents a higher variability source thansize classes (Fig. 6). For algae incubated underPAR+UVA+UVB this situation was evident (between17% and 36%), however the within-group dispersion(S.D.) for these samples was higher in the size-class axis(from 13 to 40%). In algae irradiated under PAR+UVA, decreases in photosynthesis were less scattered,and values were mainly computed around 20% for bothaxes. Similarly, under PAR treatments, inhibition ofphotosynthesis was <8%.

Table 3 Longitudinal profiles of photoinhibition of photosynthesis(%) in L. nigrescens after exposure for 48 h to three differentconditions of UV radiation and PAR using cut-off filters

Thallus parts/treatments Exposure time (h)

12 24 48

FrondsPAR+UVA+UVB 27.13±7.93e 35.08±6.77e 41.13±9.63ePAR+UVA 10.52±3.56c 13.77±1.82d 16.45±5.06dPAR 4.65±2.90b 6.62±3.39c 5.75±1.39bStipePAR+UVA+UVB 6.72±3.10c 18.50±5.40d 12.42±2.35dPAR+UVA 6.59±1.78b 13.28±5.52 10.81±4.07cPAR 0±0 3.24±2.52b 2.58±1.52bHoldfastPAR+UVA+UVB 12.12±8.8d 19.99±2.79d 18.34±6.74dPAR+UVA 10.02±3.71c 21.33±4.52 11.22±2.17cPAR 10.84±1.28c 7.51±0.80c 7.31±8.33cThree-way ANOVAMain factors MS F-valuesThallus part (A) 1319.59 F(2; 145)=59.51**Time (B) 413.75 F(2; 145)=18.66**Treatment (C) 2533.93 F(2; 145)=114.27**Interaction(A·B) 105.61 F(4; 145)=4.76*(A·C) 961.43 F(4; 145)=43.36**(B·C) 79.95 F(4; 145)=3.6*(A·B·C) 44.55 F(8; 145)=2.01 ns

Photoinhibition rates were estimated in relation to an initial con-trol. Data are means ± S.D., n=10–20. Results of the three-wayANOVA are also indicated. Similar letters connect homogeneousmeans (P<0.05, Tukey HSD)*P<0.01;**P<0.001

Fig. 5 Photoinhibition of photosynthesis (%) in fronds of L.nigrescens from three size classes after exposure for 48 h to threedifferent conditions of UV and PAR using cut-off filters.Photoinhibition rates were estimated in relation to an initialcontrol. Data are means ± S.D., n=10–20. Results of the three-way ANOVA and Tukey test are described in text

236

Discussion

UV wavelengths and photoinhibition of photosynthesis

Photosynthesis of L. nigrescens was affected byUV radiation in the experimental treatments.BEDphotoinhibition300 between 400 and 800 kJ m�2 re-sulted in approximately 40% decrease in photosynthesis.In the treatments without UVB, the photosynthesis de-creased by 17% at BED of 200 kJ m�2. These resultsfrom UV exposures with daily doses corresponding tocloudless summer days in Valdivia (40�S) confirm pre-vious findings indicating the UV susceptibility of algaeinhabiting the lower intertidal zones in this region(Gomez et al. 2004). Because the algae were subjected tolow PAR conditions during the exposure, the decline inphotosynthesis mainly reflects the effects of UV radia-tion. Furthermore, the results from the short-termexposure indicated low or no recovery of photosynthesisin algae during 12 h under shaded conditions. It is wellknown that PAR mainly causes dynamic photoinhibi-tion, i.e. a photoprotective mechanism that involves areversible down-regulation of the PSII, whereas UVBradiation delays recovery and under elevated UVB ir-radiances photosynthesis can be strongly impaired(Hanelt 1998).

The effects of UV radiation on photosynthesis of thespecies of Laminariales from the northern hemispherehave been relatively well documented especially at aphotochemical level. In general, susceptibility of pho-tosynthesis to UV radiation, measured as chlorophyllfluorescence, varies in relation to the position on theshore (Aguilera et al. 1999; Bischof et al. 1998; Apprill

and Lesser 2003) and to endogenous factors such as lifehistory phase and ontogeny (Hanelt et al. 1997; Wie-ncke et al. 2000). In the case of L. nigrescens, a highersusceptibility of photosynthesis to UV radiation ascompared to upper/midlittoral algae (e.g. Enteromor-pha) has previously been found. Similar responses werereported for the giant kelp Macrocystis pyrifera fromthe same site and location on the shore, which exhibitedthe highest UVB-related decreases of photosynthesiswithin 18 intertidal species (Gomez et al. 2004). If oneemphasizes the extent of the light stress versus depthdistribution, then algae from the lower intertidal shoresare less exposed to full solar radiation than algaegrowing at upper locations (Hanelt et al. 1994). Even insubtidal species, such as Laminaria saccharina, amarked photoinhibition occurs at ebb tide, while pho-tosynthesis recovers during rising tide (Gevaert et al.2003). Interestingly, in algae like Lessonia, the perennialcharacteristics, and hence a prolonged life-span, allowthe algae to develop and ‘‘test’’ different morpho-physiological mechanisms in response to changing(daily, seasonal, interannual) solar radiation conditions.On the other hand, the complex population dynamicsof L. nigrescens on the exposed rocky shores in central/southern Chile configures highly changing light sce-narios: cycles of mortality and recruitment modify algaldensity (Santelices and Ojeda 1984; Westermeier et al.1994) and consequently permit incident light to pene-trate under the canopy. For small, early recruitedplants growing commonly in shaded areas under thecanopy of adult algae, enhanced incident solar radia-tion after a removal of the oldest individuals influencesthe photosynthetic metabolism; in general, youngsporophytes are more sensitive to solar stress (includingUV radiation) than adult individuals (Dring et al. 1996;Hanelt et al. 1997).

Morpho-functional components of UV responses

The thallus parts of L. nigrescens have different physi-ological performance. The fronds appear to be the keyelements as photosynthetic processes particularly elec-tron transport and carbon fixation were significantlyhigher in this region than in the stipes and holdfasts.However, the photochemical attributes, such as quan-tum efficiency (Fv/Fm), were similar along the thallus(Table 2), indicating that the whole alga is undifferen-tiated in terms of its capacity for photon capture(comparable pigment contents on an area basis).However, when the discs from the different thallus re-gions were exposed to PAR+UVA+UVB, decreases inthe maximal quantum efficiency were higher in thefronds (27–41%) as compared to the stipes (6.7–18.5%)and the holdfasts (12–19.9%). Taking into account thatunder the UVB lamps the photosynthesis of the frondsdid not recover after a 12 h exposure (probably due tophotodamage), it is possible to argue that this repre-sents the most sensitive thallus region. In terms of an

Fig. 6 The relationship of the photoinhibition of photosynthesisbetween different thallus parts and size classes in L. nigrescens.Percentage photoinhibition was estimated as a decrease in Fv/Fm

relative to the initial control. Axes represent the variability(means ± S.D.) for three different UV treatments. Thallus parts= holdfast, stipes and fronds; holdfast size classes =<10 cm,10–20 cm and >20 cm

237

ecological strategy, two major factors contribute to thissituation: (a) the fronds in L. nigrescens are aerialstructures, and thus are more exposed to solar radia-tion than the stipes and the holdfasts, which generallyremain under shaded conditions under the canopy, and(b) the fronds are multiple, have a high turnover rateand allocate less energy and biomass than the stipesand holdfasts (Westermeier and Gomez 1996). Thendecreases in photosynthesis (not only due to solarstress) in the fronds can more easily be compensateddue to their dynamic demography. The strategy impliesa compromise between a rapid growth of new fronds inorder to guarantee photosynthetic tissue and a thresh-old of tolerance to solar stress that allows frond toperform metabolic activities. In our study, fronds ex-posed for 12 h to UVB exhibited marked decrease inphotosynthesis and no recovery was recorded. Thiscould be associated to chronic photoinhibition with asubsequent irreversible damage of components of thephotosynthetic apparatus, e.g. D1 proteins (Russellet al. 1995) or RuBisCo (Bischof et al. 2000). However,reductions in quantum yield of fluorescence (Fv/Fm) dueto UV not always are strictly correlated to reductionsin e.g., O2 evolution or RuBisCo activity, which wouldbe UV targeted independently of the primary photo-synthetic reactions (Laisk et al. 1992; Allen et al. 1997).

Lessonia nigrescens inhabits wave-battered rockyshores and thus its morpho-functional characteristics arestrongly determined by wave exposure (Santelices et al.1980). In this sense, the biomass is allocated in the mostcompact thallus parts, the holdfasts and stipes, bothdesigned basically to support the fronds and to with-stand mechanical tensions due to waves. In contrast, thefronds are multifunctional structures concentratingmuch of the metabolic and life-history processes of thisalga, e.g., photosynthesis, growth and reproduction.Morphologically, they are highly plastic attaining a di-vided intercalary meristem, which through a successivesplitting produces main and secondary stipes. Therefore,non-lethal effects of UVB on the fronds would havehigher consequences for algal metabolism (not for sur-vival) than if the stipes and holdfasts were primarilytargeted. The question whether UVB affects the mor-pho-function in stipes and holdfasts in the naturalhabitat, e.g., flexibility of stipes or detachment of hold-fast, has not been addressed.

In large brown algae, physiology varies as a functionof the intra-thallus location and concomitantly with age(ontogeny) (Khailov 1976; Gomez et al. 1996). Lightrequirements for photosynthesis as well as the opticalcharacteristics vary in relation to thallus thickness(Ramus 1978). Thereby, algae can attain differentphotobiological characteristics during their life cycle(Khailov et al. 1978). A relationship between size andUV sensitivity has been addressed in microalgae,emphasizing that in larger cells detrimental effects ofUV radiation can be ameliorated in virtue of theirlonger cross-section and pathlength for UV absorption(Garcıa-Pischel 1994; Karentz 1994). In the case of

macroalgae, few data on these topics are available.Some evidence indicates that early stages of sporo-phytes not only are more susceptible to UV than adultindividuals but they also show lower requirements forphotosynthesis, and hence, are strongly inhibited byenhanced PAR (Hanelt et al. 1997; Gomez and Wie-ncke 1996). A marked effect of UVB on differentdevelopmental stages of early phases of Lessonia hasalso been reported, especially decreases in the sporegermination and the reproduction capacity of gameto-phytes. Such findings suggest that UV tolerance be-longs to the whole suite of adaptations related to life-history, size and form in these algae, at least whenmicroscopic and macroscopic developmental stages arecontrasted. However, if dramatic changes in the mor-phology (morphometry) and biomass allocation withinthe thallus permanently occur along with the ontogenyin adult plants, it would be interesting to examinewhether the photosynthetic UV susceptibility vary inlarge sporophytes attaining different size and form.Based on our results, the differences in the UV sensi-tivity between the algae of different size classes(<10 cm, 10–20 cm and >20 cm holdfast diameter)were erratic (Fig. 5). It is possible to argue that at thisrange of sizes (the smallest exemplar measured in ourstudy had a holdfast diameter of 5 cm) sporophyteshave already developed a massive anatomy, whosemain optical feature is a well developed self-shading.This is relevant in terms of the distribution of photo-synthetic cells: although pigments contents (hence thelight absorbing capacity) do not vary significantlyamong thallus parts on an area basis (data not shown),their different concentration on a weight basis hasecological relevance, as the holdfast and stipes aremassive structures in which pigmented, photosyntheticcells account for a minor fraction of the whole cellbiomass. Such a cell allocation pattern is exacerbatedwith increasing growth/age of the plant. Thus, a rapidincrease in thickness has two contrasting morpho-functional consequences: (a) the decrease in the ratiobetween assimilatory and non-assimilatory cells and (b)an increase in the self-shading within the thallus whichattenuate the damage from excessive solar stress whenthe young sporophytes are still vulnerable in theirnatural habitat.

Overall, our results emphasize on the longitudinalprofiles of photosynthesis in L. nigrescens and provideadditional evidence that UV radiation affect photosyn-thesis in intertidal macroalgae from southern Chile(Gomez et al. 2004). The ecological implications of theseresponses appear to be relevant for Lessonia and therebyfurther studies on acclimation potential to UV radiation,effects on carbon assimilation as well as UV protectiveand repair mechanisms are necessary.

Acknowledgements The study was financially supported by CON-ICYT-Chile (FONDECYT 1030343 to I.G). The authors thank J.Landerretche for valuable technical assistance and P. Huovinenand two anonymous reviewers for critical reading of the manu-script.

238

References

Aguilera J, Karsten U, Lippert H, Vogele B, Philipp E, Hanelt D,Wiencke C (1999) Effects of solar radiation on growth, pho-tosynthesis and respiration of marine macroalgae from theArctic. Mar Ecol Prog Ser 191:109–119

Allen DJ, MacKee IF, Farage PK, Bakker NR (1997) Analysis oflimitations to CO2 assimilation on exposure of leaves of twoBrassica napus cultivars to UV-B. Plant Cell Environ 20:633–640

Anonymous (2003) Anuario Estadıstico de Pesca. Servicio Nac-ional de Pesca, Chile

Apprill AM, Lesser MP (2003) Effects of ultraviolet radiation onLaminaria saccharina in relation to depth and tidal height in theGulf of Maine. Mar Ecol Prog Ser 256:75–85

Bischof K, Hanelt D, Wiencke C (1998) UV radiation can affectdepth-zonation of Antarctic macroalgae. Mar Biol 131:597–605

Bischof K, Hanelt D, Wiencke C (2000) Effects of ultravioletradiation on photosynthesis and related enzyme reactions ofmarine macroalgae. Planta 211:555–562

Cabello-Pasini A, Alberte RS (2001) Expression of carboxylatingenzymes in Laminaria setchelli (Phaeophyceae). Phycologia40:351–358

Drew EA, Hastings RM (1992) A year-round ecophysiologicalstudy of Himantothallus grandifolius (Desmarestiales, Pha-eophyta) at Signy Island, Antarctica. Phycologia 31:262–277

Dring MJ, Makarov, V, Schoschina E, Lorenz, Luning K (1996)Influence of ultraviolet-radiation on chlorophyll fluorescenceand growth in different life-history stages of three species ofLaminaria (Phaeophyta). Mar Biol 126:183–191

Figueroa FL, Salles S, Aguilera J, Jimenez C, Mercado J, VineglaB, Flores-Moya A, Altamirano M (1997) Effects of solar radi-ation on photoinhibition and pigmentation in the red algaPorphyra leucosticta. Mar Ecol Prog Ser 151:81–90

Garcıa-Pichel F (1994) A model for internal self-shading inplanktonic microorganisms and its implications for the useful-ness of sunscreens. Limnol Oceanogr 39:1704–1717

Gevaert F, Creach A, Davoult D, Migne A, Lavavasseur G, ArzelP, Holl A-C, Lemoine Y (2003) Laminaria saccharina photo-synthesis measured in situ: photoinhibition and xanthophyllcycle during tidal cycle 247:43–50

Gomez I, Luning K (2001) Constant short-day treatment of out-door-cultivated Laminaria digitata prevents summer drop ingrowth rate. Eur J Phycol 36: 391–395

Gomez I, Wiencke C (1996) Photosynthesis, dark respiration andpigment contents of gametophytes and sporophytes of theAntarctic brown alga Desmarestia menziesii. Bot Mar 39:149–157

Gomez I, Wiencke C, Thomas DN (1996) Variations in photo-synthetic characteristics of the Antarctic marine brown algaAscoseira mirabilis in relation to thallus age and size. Eur JPhycol 31:167–172

Gomez I, Figueroa FL, Sousa-Pinto I, Vinegla B, Perez-RodrıguezE, Maestre C, Coelho S, Felga A, Pereira R (2001) Effects ofUV radiation and temperature on photosynthesis as measuredby PAM fluorescence in the red alga Gelidium pulchellum(Turner) Kutzing. Bot Mar 44:9–16

Gomez I, Figueroa FL, Ulloa N, Morales V, Lovengreen C, Hu-ovinen P, Hess S (2004) Patterns of photosynthesis in 18 speciesof intertidal macroalgae from southern Chile. Mar Ecol ProgSer 270:103–116

Grzymski J, Johnsen G, Sakshaug E (1997) The significance ofintracellular self-shading on the bio-optical properties ofbrown, red and green macroalgae. J Phycol 33:408–414

Hanelt D (1998) The capability for dynamic photoinhibition inArctic macroalgae is related to their depth distribution. MarBiol 131:361–369

Hanelt D, Li J, Nultsch W (1994) Tidal dependence of photoin-hibition of photosynthesis in marine macrophytes of southChina Sea. Bot Acta 107:66–72

Hanelt D, Wiencke C, Karsten U, Nultsch W (1997) Photoinhibi-tion and recovery after high stress in different developmentaland life-history stages of Laminaria saccharina (Phaeophyta). JPhycol 22:387–395

Inskeep WP, Bloom PR (1985) Extinction coefficients of chloro-phyll a and b in N,N-dimethyl-formamide and 80% acetone.Plant Physiol 77:483–485

Jones LW, Kok B (1966) Photoinhibition of chloroplast reactions.1) Kinetics and action spectrum. Plant Physiol 41:1037–1043

Karentz D (1994) Ultraviolet tolerance mechanisms in Antarcticmarine organisms. In: Weiler CS, Penhale PA (eds) Ultravioletradiation in Antarctica: Measurements and Biological effects.Antarctic Research Series Vol 62, American Geophysical Un-ion, Washington DC. pp 93–110

Khailov KM (1976) The relationship between weight, length, ageand intensity of photosynthesis and organotrophy of macro-phytes in the Barent Sea. Bot Mar 19:335–339

Khailov KM, Kholodov VI, Firsov K, Prazukin AV (1978) Thalliof Fucus vesiculosus in ontogenesis: changes in morpho-physi-ological parameters. Bot Mar 21:289–311

Kremer BP (1981) Aspects of carbon metabolism in marine mac-roalgae. Oceanogr Mar Biol Ann Rev 19:41–94

Kremer BP (1984) Carbohydrate reserve and dark carbon fixationin the brown macroalga, Laminaria hyperborea. J Plant Physiol117:233–242

Kuppers U, Kremer BP (1978) Longitudinal profiles of carbondioxide capacities in marine macroalgae. Plant Physiol 62:49–53

Laisk A, Kiirats O, Oja V, Gerts U, Weis E, Heber U (1992)Analysis of oxygen evolution during photosynthetic inductionand in multiple turnover flashes in sunflower leaves. Planta186:434–441

Lovengreen C, Fuenzalida H, Villanueva L (2000) Ultraviolet solarradiation at Valdivia, Chile (39,8� S). Atmos Environ 34:4051–4061

Luning K, Schmitz K, Willenbrink J (1973) CO2 fixation andtranslocation in benthic marine algae. III. Rates and ecologicalsignificance of translocation in Laminaria hyperborea and L.saccharina. Mar Biol 23:275–281

Mercado JM, Jimenez C, Niell FX, Figueroa FL (1996) Compar-ison of methods for measuring light absorption by algae andtheir application to the estimation of the package effect. SciMar 60:39–45

Nunez M, Alveal K (1988) Estructuras cribadas en algunas algaspardas Chilenas. Gayana Bot 45:371–378

Ojeda P, Santelices B (1984) Ecological dominance of Lessonianigrescens (Phaeophyta) in Central Chile. Mar Ecol Prog Ser19:1–12

Ramus J (1978) Seaweed anatomy and photosynthetic perfor-mance: the ecological significance of light guides, heterogeneousabsorption and multiple scatter. J Phycol 14:352–362

Russell AW, Critcheley C, Robinson SA, Franklin LA, SeatonGGR, Chow WS, Anderson JM, Osmond CB (1995) Photo-system II regulation and dynamic of chloroplast D1 protein inArabidopsis leaves during photosynthesis and photoinhibition.Plant Physiol 107:943–952

Santelices B (1989) Algas marinas de Chile. Ediciones UniversidadCatolica de Chile, Santiago

Santelices B, Ojeda P (1984) Recruitment, growth and survival ofLessonia nigrescens (Phaeophyta) at various tidal levels in ex-posed habitats of central Chile. Mar Ecol Prog Ser 19:73–82

Santelices B, Castilla JC, Cancino J, Schmiede P (1980) Compar-ative ecology of Lessonia nigrescens and Durvillaea antarctica(Phaeophyta) in central Chile. Mar Biol 59:119–132

Schaffelke B (1995) Storage carbohydrates and abscisic acid con-tents in Laminaria hyperborea are entrained by experimentaldaylengths. Eur J Phycol 30:313–317

Schreiber U, Bilger W, Neubauer C (1994) Chlorophyll fluores-cence as a non-intrusive indicator for rapid assessment of invivo photosynthesis. In: Schulze ED, Caldwell MM (eds) Eco-physiology of photosynthesis. Ecological Studies. Vol 100.Springer, Berlin Heidelberg New York, pp 49–70

239

Vasquez JA, Santelices B (1990) Ecological effects of harvestingLessonia (Laminariales, Phaeophyta) in central Chile. Hydro-biologia 204/205:41–47

Westermeier R, Gomez I (1996) Biomass, energy contents andmajor organic compounds in the brown alga Lessonia nigres-cens (Laminariales, Phaeophyceae) from Mehuın, south Chile.Bot Mar 39:553–559

Westermeier R, Muller DG, Gomez I, Rivera PJ, Wenzel H (1994)Population biology of Durvillaea antarctica and Lessonia

nigrescens (Phaeophyta) on the rocky shores of southern Chile.Mar Ecol Prog Ser 110:187–194

Wiencke C, Gomez I, Pakker H, Flores-Moya A, Altamirano M,Hanelt D, Bischof K, Figueroa FL (2000) Impact of UV-radi-ation on viability, photosynthetic characteristics and DNA ofbrown algal zoospores: implications for depth zonation. MarEcol Prog Ser 197:217–229

240