BIOLOGIA PLANTARUM 38 (3): 413-420, 1996 Photosynthesis of natural cocksfoot populations under water and salt stresses P. RAMOS, N. PEDROL and M. J. REIGOSA* Fisiologia Vegetal, Departamento de Recursos Naturales y Medto Ambiente, Facultad de Ctencias, Universldad de Vigo, Apdo 874, 36200 Vigo, Spain Abstract Sampling of natural cocksfoot (Dacfylis glomerata L.) populations was carried out on the O Morrazo peninsula in NW Spain, characterized by a strong moisture gradient. The plants were kept in greenhouse under standard conditions. Nevertheless, they differ in height of plants, length and width of flag leaves, panicle size, stomatal density and size as well as in flowering period. The effects of two levels of soil water deficit and two levels of salinity on photosynthetic rate were tested. One population was exceptionally well adapted to its original environment with great tolerance to water deficit and salinity. Additional key words: Dactylis glomerata L., Gramineae ecophysiology. Introduction To understand the distributional limits of plants it is proposed to uncover the physiological responses to suboptimal environmental conditions, that is, when absorption of water or nutrients, the process of photosynthesis, respiration, etc., are limited during some part of the life cycle of the plant (Levitt 1980, Salisbury and Ross 1992). Our interest is centered on the study of a grass species, Dac(ylis glomerata L., whose great adaptive potential allows it to colonize very diverse ecosystems. Numerous subspecies have been described with different cytotypes: diploid, tetraploid and hexaploid (Stebbins and Zohary 1959, Borril 1961, Lumaret et al. 1987, Ortiz and Rodriguez-Oubifia 1993). In Galicia there is sympatry between Received 30 October 1995, accepted 23 January 1996. Acknowledgements: The authors would like to thank the Xunta de Galicia (XUGA 3010 4B 92) as well as the DGICYT (PB92-0321) and the Universityof Vigo (60902.C.227), for financingprojects which include this one. We would like to express our most sincere thanks to Marina Horjales and Nieves Redondo of the Universityof Vigo for their collaborationand Carlos Bolafiofor his skilfuU assistance. * To whom correspondenceshouldbe sent. FAX 34-86-812556. 413