Water Status and Leaf Elongation of$C_{3}-$and C4Grasses of Flooding Pampa Grassland

Question: Do warm season (i.e. mainly C4) grass species exhibit a higher water status than winter-growing competitors, (mainly C3plants) and is this part of their competition ability? Location: Flooding Pampa grassland at Balcarce, eastern Argentina. Methods: Predawn leaf water potential was measured in five species: (1) three cool-season species: Festuca arundinacea, Lolium multiflorum and Stipa neesiana, and (2) two warm-season species: Sporobolus indicus and Paspalum dilatatum, throughout a summer season. The sensitivity of leaf growth to low water status was investigated in a greenhouse experiment where plants were grown in pots at three levels of water deficit. Results: The field study revealed strong differences of water status between the five species likely indicating large contrasts in soil water availability, irrespective of their photosynthetic metabolism. By contrast, the response of leaf elongation rate to predawn water potential was similar in all species studied. Species to which water was less available did not compensate with a lesser sensitivity to water status. Conclusion: Competition for water may play an important and specific role within natural semi-grasslands of these regions, independently of the metabolic pathway of grasses.