ORIGINAL ARTICLE Alfredo O. Saldan˜a • Carolina Herna´ndez Rafael E. Coopman • Leo´n A. Bravo Luis J. Corcuera Differences in light usage among three fern species of genus Blechnum of contrasting ecological breadth in a forest light gradient Received: 17 February 2009 / Accepted: 16 September 2009 / Published online: 6 November 2009 Ó The Ecological Society of Japan 2009 Abstract In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse micro- habitats in a light gradient. We hypothesized that dif- ferences in the habitat preferences of three co-occurring Blechnum species would be associated with differences in the magnitude of responses of light capture [chlorophyll (Chl) content] and use (photosynthetic capacity and performance) to light availability. We measured the abundance, chlorophyll content, photosynthetic capac- ity (A), and photosynthetic performance (chlorophyll fluorescence of photosystems I and II) of juvenile indi- viduals of each species growing in different light levels in the field. While Blechnum magellanicum covers a broad light environments range, B. mochaenum is restricted to shade, and B. penna-marina occupies full sun sites. Despite significant interspecific differences in average total chlorophyll content, this trait did not differ among species along the light gradient. There was significant interspecific variation in both the mean value and the plasticity of Chl a:Chl b ratio and A to light availability. While B. penna-marina showed a flatter reaction norm (lower response) of Chl a:Chl b ratio to light availability than its two congeners, B. mochaenum showed a lower response of A to light availability. B. penna-marina and B. magellanicum individuals from open sites had higher light saturation points of the electron transport rate (ETR) of both photosystems (ETR LSP I and II) and photochemical quenching (qL and NA) than the shade restricted B. mochaenum. Additionally, non-pho- tochemical quenching values for both photosystems (NPQ and ND) were higher in ferns species occurring in shaded sites. The adjustment of the photosynthetic capacity and performance to light availability appears to be an important mechanism of acclimation in these three Blechnum species that differ in their habitat preferences across a light gradient. Keywords Ecological breadth Æ Forest light gradient Æ Blechnum Æ Chlorophyll content and fluorescence Æ Photosynthetic capacity Introduction Most pteridophytes live in moist and shady environments (Page 2002; Aldasoro et al. 2004; Karst et al. 2005), mainly because fern species are dependent upon a moist envi- ronment for growth of their nonvascular gametophyte generation. In addition, hydraulic characteristics of fern foliage result in poor control of water conduction and loss (Woodhouse and Nobel 1982; Robinson 1994; Brodribb and Holbrook 2004). Nonetheless, some fern species are able to recruit in high-irradiance sites (Saldan˜ a et al. 2005, 2007), thus having a wide ecological breadth despite the above constraints. Moreover, there are fern species that occupy almost exclusively open sites (Banister and Fagan 1989). It is widely known that plant species growing across different light environments should be able to produce leaves that are morphologically and physiologically suited to a wide range of light environments (Bjo¨rkman 1981; Walters and Field 1987; Lambers et al. 1998). Heteroge- neity of light environments can influence photosynthetic performance of ferns by means of a direct effect on the photosynthetic apparatus and its damage under stress conditions (Valladares and Pearcy 1997; Lambers et al. 1998; Walters 2005). The balance between the light energy absorbed and that used for metabolism is critical in pho- tosynthetic organisms (Hu¨ner et al. 2002), hence for the maintenance of a positive carbon balance in a wide range of environments and for successfully occupying diverse habitats (Chazdon 1992; Spencer et al. 1994). A. O. Saldan˜a (&) Æ C. Herna´ndez Æ L. A. Bravo Æ L. J. Corcuera Departamento de Bota´nica, Universidad de Concepcio´n, Casilla 160-C, Concepcio´n, Chile E-mail: asaldana@udec.cl Tel.: +56-41-2204418 Fax: +56-41-2246005 R. E. Coopman Instituto de Silvicultura, Facultad de Ciencias Forestales, Universidad Austral de Chile, Valdivia, Chile Ecol Res (2010) 25: 273–281 DOI 10.1007/s11284-009-0656-8