PHOTOSYNTHETICA 42 (3): 371-376, 2004 371 Leaf physiological traits and their importance for species success in a Mediterranean grassland J.T. TSIALTAS *,*** , T.S. PRITSA ** , and D.S. VERESOGLOU * Aristotle University of Thessaloniki, School of Agriculture, Laboratory of Ecology & Environmental Protection (267) * and Laboratory of Biology of Horticultural Plants ** , 541 24 Thessaloniki, Greece Abstract We related leaf physiological traits of four grassland species (Poa pratensis, Lolium perenne, Festuca valida, and Taraxacum officinale), dominant in a Mediterranean grassland, to their origin and success at community level. From early May to mid-June 1999, four leaf samplings were done. Species originating from poor environments (P. pratensis, F. valida) had low carbon isotope discrimination (∆), specific leaf area (SLA), leaf water and mineral contents, and net photosynthetic rate on mass basis (P mass ) but high chlorophyll content. The reverse traits were evident for the fast- growing species (L. perenne, T. officinale). Under the resource-limiting conditions (soil nitrogen and water) of the Mediterranean grassland, the physiological traits of P. pratensis and F. valida showed to be more adapted to these conditions leading to high species abundance and dominance. Additional key words: carbon isotope discrimination; chlorophyll; leaf water content; nitrogen; photosynthesis; specific leaf area. Introduction Plants are grouped, according to their Relative Growth Rate (RGR), to fast- and slow-growing species with fast- growing ones being more adapted to rich environments while slow-growing ones succeed better in poor habitats (Poorter and Bergkotte 1992, van Arendonk and Poorter 1994, Reader 1998). Leaf anatomy and chemical compo- sition are related to species RGR and considered to be a determinant factor for species adaptation to different environments (Lambers and Poorter 1992). In general, fast-growing species are characterized by high specific leaf area (SLA, the ratio of the leaf area per g leaf dry mass) or low areal leaf mass (ALM, the ratio of leaf dry mass per leaf area unit, i.e. the SLA reciprocal), high water content, high nitrogen content, and low investment in the photosynthetic machinery. Their leaves have a short life span and show lower construction cost [kg(glucose) kg -1 (dry matter)], compared to the slow- growing species (Poorter and Remkes 1990, Poorter et al. 1990, Poorter and Bergkotte 1992, Shipley 1995, Poorter and Evans 1998, Baruch and Goldstein 1999). Further- more, significant differences exist between fast- and slow-growing species in leaf anatomy and chemical composition, as previously mentioned. Specifically, fast- growing species are characterized by thick leaves with wide mesophyll and high contents of minerals and organic N-compounds. Slow-growing species have more rigid cell walls and invest more in secondary compounds such as lignin and (hemi-)cellulose (van Arendonk and Poorter 1994, van Arendonk et al. 1997). Species from resource-rich environments are directed to resource capture and thus show higher net photosynthetic rates (P N ) and photosynthetic nitrogen use efficiency (PNUE, the amount of assimilated CO 2 per unit leaf nitrogen), compared to species from poor environments (Lambers and Poorter 1992, Poorter and Evans 1998). In water limited environments (poor environments), high water use efficiency (WUE) has been considered as a trait contributing to species success at the community level (Ehleringer 1993, Tsialtas et al. 2001). Since carbon isotope discrimination (∆), which depends on the ratio of intercellular and ambient partial pressures of CO 2 (p i /p a ), is negatively related to transpiration efficiency for C 3 species (Farquhar et al. 1989, Turner 1997), it is expected that species would be differentiated in their ∆ values ——— Received 24 October 2003, accepted 7 June 2004. *** Corresponding author; present address: Hellenic Sugar Industry SA, Larissa factory, Department of Experimentation, 411 10 Larissa, Greece; fax: +30 2410 575119, e-mail: tsialtas01@hotmail.com Acknowledgements: We thank Dr C.M. Scrimgeour at Scottish Crop Research Institute for the analyses of elemental and isotopic composition of the samples and P. Skenteridis for his help during the experimentation. This research was funded by the Ministry of Industry, Energy, and Technology of Greece and was partially supported by scholarships provided to the first two authors by the Greek National Scholarship Foundation.