CHANGES IN NUTRIENT CONTENT OF PALMARIA PALMATA IN RESPONSE TO VARIABLE LIGHT AND UPWELLING IN NORTHERN SPAIN 1 Brezo Martı´nez A ´ rea de Biodiversidad y Conservacio ´n, Escuela Superior de Ciencias Experimentales y Tecnologı ´a, Universidad Rey Juan Carlos, C ⁄ Tulipa ´n s ⁄ n, E-28933 Mo ´stoles, Madrid, Spain and Jose M. Rico 2 A ´ rea de Ecologı ´a, Dpto. Biologı ´a de Organismos y Sistemas, Universidad de Oviedo, C ⁄ Catedra ´tico Rodrigo Urı ´a s ⁄ n, E-33071 Oviedo, Spain Light has been identified as one of the main factors affecting seaweed ecophysiology. We investi- gated the dependence of nutrient metabolism on sun and shade light conditions and whether epi- sodes of upwelling of nutrient-rich subsuperficial water could reduce the summer nutrient limitation driving physiological changes in Palmaria palmata (L.) Kuntze. We measured the major nutrient pools, photosynthetic pigments, and light curves, under sun and shade conditions during a summer period when one upwelling was recorded. The redundancy analysis (RDA) produced two clear groups: sun- and shade-acclimated algae. Light was the major predic- tive factor. Sun-acclimated algae exhibited higher carbon (C) and lower nitrogen (N) and phosphorus (P) content in association with the storage of flor- idoside (main C reserve) to benefit from higher irra- diance (under nutrient limitation). Among N pools, N reserves (phycoerythrin, nitrate) were a lower pro- portion of the total N in sun-acclimated algae, sug- gesting their degradation to fulfill the N demands of the cell. The orthophosphate content was also lower in sun-acclimated algae, indicating its utiliza- tion as a nutrient reserve. In contrast, N within cell walls and membranes and chl a contributed to a similar proportion of the total N in sun- and shade- acclimated algae, suggesting a response to sustain cell integrity. Transient high nutrient concentration due to the upwelling was unrelated to the nutrient content of the thallus. The storage of C as florido- side from high light exposure was shown to be the driving force for the metabolic adjustment of P. palmata at the end of summer before the onset of dormancy. Key index words: carbon; light; nitrogen; nutrient; Palmaria palmata; phosphorus; shade; sun; upwelling Abbreviations: DIVING-PAM, underwater port- able pulse amplitude fluorometer; DMF, N, N-dimethylformamide; ETR, apparent photo- synthetic electron transport rates; FAA, free amino acids; PC, phycocyanin; PCA, principal component analysis; PE, phycoerythrin; RDA, redundancy analysis; TIN, total insoluble nitrogen Light environment has been identified as the key factor affecting the physiology of autotrophs (Lu ¨n- ing 1990, Dring 1992, Lo ´pez-Figueroa 1992, Kirk 1994, Lobban and Harrison 1997, Prescott et al. 1999, Buchanan et al. 2000). Plant canopies signifi- cantly decrease irradiance, reducing light penetra- tion and causing major changes in light quality (i.e., green and far-red light are enriched compared to red or blue light; Smith 1982, Kirk 1994, Salles et al. 1996). Acclimation to such changes is common in macroalgae (Lo ´ pez-Figueroa et al. 1990, Ru ¨ diger and Lo ´pez-Figueroa 1992, Talarico 1996, Talarico and Maranzana 2000, Figueroa et al. 2003a) as well as phytoplankton and seagrasses (Kirk 1994). Typi- cally, shade-acclimated plants synthesize photosyn- thetic pigments, such as chl and phycobilins, to enhance their efficiency in absorbing energy at sub- saturating irradiances (Ru ¨diger and Lo ´pez-Figueroa 1992, Salles et al. 1996, The ´ry 2001, Figueroa et al. 2003a), and they show lower light-saturation values in light-response curves (Beach and Smith 1996, Sagert and Schubert 2000, The ´ry 2001, Figueroa et al. 2003b). Moreover, a wide range of metabolic responses, including enhancement of C fixation in sun conditions and reallocation of nutrient-rich con- stituents within the thallus, is also common (Young and Smith 1980, Lo ´pez-Figueroa and Ru ¨ diger 1991, Lo ´pez-Figueroa 1992, Figueroa 1993, Vergara 1993, Figueroa 1996, Ha ¨der et al. 1997, McGlathery and Pedersen 1999, Figueroa et al. 2003b). These eco- physiological responses have been identified among the various factors that result in the efficient cap- ture and utilization of incident radiant energy by macroalgae and thus influence the potential competitive ability of each species (see review in Carpenter 1990). 1 Received 8 September 2006. Accepted 26 June 2007. 2 Author for correspondence: e-mail jmrico@uniovi.es. J. Phycol. 44, 50–59 (2008) Ó 2008 Phycological Society of America DOI: 10.1111/j.1529-8817.2007.00440.x 50