ORIGINAL PAPER Effects of simulated herbivory on photosynthesis and N resorption efficiency in Quercus pyrenaica Willd. saplings Silla Fernando Æ Fleury Marina Æ Mediavilla Sonia Æ Escudero Alfonso Received: 11 October 2007 / Revised: 13 February 2008 / Accepted: 13 May 2008 / Published online: 6 June 2008 Ó Springer-Verlag 2008 Abstract We examined the effects of simulated folivory by caterpillars on photosynthetic parameters and nitrogen (N) resorption efficiency in Quercus pyrenaica saplings. We analyzed the differences between intact leaves in control plants, punched leaves in damaged plants, and intact leaves in damaged plants. We then established two levels of simulated folivory: low (&13% of the leaf area of one main branch removed per plant) and high (&26% of the leaf area of one main branch removed per plant) treatments. No differences were found in net assimilation rate and conductance between either leaf type or treatment during the most favourable period for photosynthesis. However, the N content was lower in punched than in intact leaves, and as a result PNUE was higher in damaged leaves from treated trees. In leaf-litter samples, N mass was significantly higher in punched than in intact leaves in treated plants, and LMA was significantly higher in dam- aged than in intact leaves of both the treated and control plants. Consequently, N resorption efficiency was around 15% lower in damaged leaves as compared with intact leaves from treated and control plants. Mechanical injury to leaves not only triggered no compensatory photosyn- thetic response to compensate a lower carbon uptake due to leaf area loss, but also affected the resorption process that characterizes leaf senescence. Keywords Compensatory photosynthetic response Á Herbivory Á N resorption efficiency Á PNUE Á Quercus pyrenaica Introduction Compensatory responses of plants to damage by herbi- vores have been found in several species as a mechanism to reduce detrimental effects on survival, growth, and reproduction. In this sense, compensatory photosynthesis, defined as an increase in photosynthetic rates in partially defoliated plants with respect to intact ones (Nowak and Caldwell 1984), is one of the best-documented responses (Nowak and Caldwell 1984; Welter 1989; Dyer et al. 1991; Oleksyn et al. 1998; Thomson et al. 2003; Retuerto et al. 2004). Compensatory photosynthesis can affect the remaining area of damaged leaves, or may extend towards intact leaves in damaged trees (Welter 1989; Retuerto et al. 2004). Most of the mechanisms invoked to account for compensatory photosynthesis generally fall into two categories: (a) an increase in limiting resources (light, water and/or nutrients) in the remaining foliage (McNaughton 1983; Nowak and Caldwell 1984; Anten and Ackerly 2001), and (b) an increase in the strength of the sink demand of carbon with respect to the source supply, known as the ‘‘sink-source hypothesis’’ (Dyer et al. 1991; Oleksyn et al. 1998; Thomson et al. 2003; Retuerto et al. 2004). Communicated by F. M. Canovas. S. Fernando (&) Á M. Sonia Á E. Alfonso A ´ rea de Ecologı ´a, Facultad de Biologı ´a, Universidad de Salamanca, Campus Unamuno, 37007 Salamanca, Spain e-mail: fsilla@usal.es F. Marina Laborato ´rio de Ecologia e Restaurac ¸ao ˜ Florestal (LERF), Escola Superior de Agricultura ‘‘Luiz de Queiroz’’, Universidade de Sa ˜o Paulo (ESALQ/USP), Sa ˜o Paulo, Brazil F. Marina Grupo de Fenologia e Dispersa ˜o de Sementes (GFDS), Universidade Estadual Paulista (UNESP), Sa ˜o Paulo, Brazil 123 Trees (2008) 22:785–793 DOI 10.1007/s00468-008-0239-2