Leaf gas exchange, water status and radiation use efficiency of giant reed (Arundo donax L.) in a changing soil nitrogen fertilization and soil water availability in a semi-arid Mediterranean area

The aim ofthe present work was to ascertain, in a two-year field trial, leaf gas exchange, plant water status and radiation use efficiency of giant reed (Arundo donax L.) under different nitrogen fertilization and soil water availability in semi-arid Mediterranean area. Three levels of nitrogen (0, 60 and 120 kg N ha-1) and three levels of soil water availability (rainfed, 50% ETm restitution and 100% ETm restitution) were compared. Throughout the crop growing season significant effects of soil water availability, nitrogen fertilization and time of measurement on net photosynthesis (A), transpiration rate (E), stomatal conductance (gs), canopy temperature (Tc), midday (M) and predawn leaf water potential (PD) were found. Significant interactions of soil water availability x time of measurement were also observed, while nitrogen x time of measurement was significant only for A, gs, E and M. Radiation use efficiency (RUE) was lowest in rainfed and no-nitrogen fertilization (1.40 and 1.26 g MJ-1 in 1998 and in 1999, respectively) and highest in 100% ETm and 120 kg N ha-1 in both years (1.78 and 1.94 g MJ-1 in 1998 and in 1999, respectively). The fraction of intercepted PAR approached the asymptote when leaf area index was greater than 4.0, irrespective of soil water availability and nitrogen fertilization. The extinction coefficient (k) ranged from 0.38 to 0.44. Present results may have practical applications to help maximize physiological performances with improved WUE, optimized resource use efficiency and reduced irrigation demands.