Involvement of nodule N metabolism in the improvement of water use efficiency in drought-stressed alfalfa (Medicago sativa L.) grown with sewage sludge

MARIA LAURA FIASCONARO; MANUEL SÁNCHEZ-DÍAZ; MARIA CARMEN ANTOLÍN

Castelló de la PLana

Congreso; XIX Reunión de la Sociedad Española de Fisiología Vegetal/ XII Congreso Hispano-Luso de Fisiología Vegetal; 2011

nitrate and ammonium from the soil solution, or from atmospheric N (N2) fixation through asymbiotic association with N2-fixing bacteria. Thus, the operation of both metabolic processescould contribute to alleviate the impact of drought in sludge-treated plants. A greenhouseexperiment was conducted to evaluate the involvement of nodule N metabolism on the efficientuse of resources such as water and nitrogen in sludge-treated plants. The experiment includedthree treatments: (1) plants inoculated with rhizobia and amended with sewage sludge at rate of10% (w/w) (RS); (2) plants inoculated with rhizobia without any amendment (R); and (3) noninoculatedplants fed with ammonium nitrate (N). Two levels of irrigation were imposed: (1)well-watered and (2) drought stress during several cycles of moisture stress and recovery. Underdrought, sludge-treated plants had increased plant growth and higher photosynthetic and wateruse efficiencies (A/gw and PNUE) than untreated plants; moreover, there was no effect on themost relevant N2 fixation-related parameters (PEPC, MDH and leghemoglobin) whereas astimulation of NR and the GS/GOGAT activities was found. Results clearly showed that underdrought, the concurrence of both N2 fixation and N assimilation in sludge-treated nodules couldresult in improved drought tolerance of alfalfa plants.