MORPHO-FUNCTIONAL PATTERNS OF PHOTOSYNTHESIS IN THE SOUTH PACIFIC KELP LESSONIA NIGRESCENS: EFFECTS OF UV RADIATION ON 14 C FIXATION AND PRIMARY PHOTOCHEMICAL REACTIONS 1 Iva´n Go´mez, 2 Marcela Orostegui Instituto de Biologı ´a Marina, Universidad Austral de Chile, Isla Teja s/n, PO Box 567, Valdivia, Chile and Pirjo Huovinen Department of Biological and Environmental Science, University of Jyva ¨skyla ¨, PO Box 35 (Survontie 9), FIN-40351 Jyva ¨skyla ¨, Finland; and Centro de Investigacio ´n y Desarrollo de Recursos y Ambientes Costeros ‘‘i-mar,’’ Universidad de Los Lagos, Camino a Chinquihue km. 6, PO Box 557, Puerto Montt, Chile The morpho-functional patterns of photosynthe- sis, measured as 14 C-fixation and chl fluorescence of PSII, also as affected by different doses of UV ra- diation in the laboratory were examined in the South Pacific kelp Lessonia nigrescens Bory of the coast of Valdivia, Chile (401 S). The results indicated the existence of longitudinal thallus profiles in physiological performance. In general, blades exhibited higher rates of carbon fixation and pig- mentation as compared with stipes and holdfasts. Light-independent 14 C fixation (LICF) was high in meristematic zones of the blades (3.5 lmol 14 C . g  1 fresh weight [FW] . h  1 ), representing 2%–16% (percentage ratio) of the photosynthetic 14 C fixation (20 lmol 14 C . g  1 FW . h  1 ). Exposures to UV radi- ation indicated that biologically effective UV-B doses (BED photoinhibition300 ) of 200–400 kJ . m  2 (cor- responding to current daily doses measured in Valdivia on cloudless summer days) inhibit photo- synthetic 14 C fixation of blades by 90%, while LICF was reduced by 70%. The percentage ratio of LICF to photosynthetic 14 C fixation increased under UV exposure to 45%. Primary light reactions measured as maximum quantum yield (F v /F m ) and electron transport rate (ETR) indicated a higher UV suscep- tibility of blades as compared with stipes and hold- fasts: after a 48 h exposure to UV-B, the decrease in the blades was close to 30%, while in the stipes and holdfasts it was <20%. The existence of transloca- tion of labeled carbon along the blades suggests that growth at the meristem may be powered by non- photosynthetic processes. A possible functional role of LIFC, such as during reduction of photosynthetic carbon fixation due to enhanced UV radiation, is discussed. These results in general support the idea that the UV-related responses in Lessonia are inte- grated in the suite of morpho-functional adapta- tions of the alga. Key index words: carbon fixation; chlorophyll fluorescence; Lessonia nigrescens; light-independent carbon fixation; photosynthesis; translocation; UV radiation Abbreviations: BED, biologically effective doses; ETR, electron transport rate; LICF, light-independ- ent carbon fixation; PEPC, phosphoenol pyruvate carboxylase; PEP-CK, phosphoenol pyruvate car- boxykinase Large Laminariales (kelps) are characterized by complex morpho-functional processes including a temporal synchronization between photosynthesis and growth as well as the long-distance transport of organic substances (Lu ¨ning et al. 1973, Schmitz 1981). Such characteristics represent strategies to cope with the marked seasonality in polar and cold-temperate regions (Chapman and Lindley 1980, Go ´mez and Lu ¨ning 2001). In contrast to filamentous or sheet- like algae, photosynthetic carbon fixation in massive brown algae does not occur uniformly along the thallus (Arnold and Manley 1985, Go ´mez et al. 1995, Cabello- Pasini and Alberte 2001), and regions of carbon syn- thesis and sink can often be identified. In general, sugars are synthesized and stored as polysaccharides (e.g., laminarin) in the distal, assimilatory tissues of the algae, from which they are then translocated as low- molecular-weight compounds (e.g., mannitol) to the growth region (Kremer 1981a, b). This morpho- functional pattern can be associated with the perenni- al characteristics: (a) the biomass allocation of the algae as a consequence of the allometric growth and the ac- tion of an intercalary meristem normally result in dif- ferent metabolic development along the thallus, and (b) due to ecological constraints (such as light availabil- ity, protection against predation, etc.), these organisms 1 Received 21 December 2005. Accepted 1 November 2006. 2 Author for correspondence: e-mail igomezo@uach.cl. 55 J. Phycol. 43, 55–64 (2007) r 2007 by the Phycological Society of America DOI: 10.1111/j.1529-8817.2006.00301.x