Relationship between photosynthetic capacity, nitrogen assimilation and nodule metabolism in alfalfa (Medicago sativa) grown with sewage sludge

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

Zaragoza

Congreso; XIII Reunión Nacional de la Sociedad Española de Fijación de Nitrógeno y II Congreso Luso-Español de Fijación de Nitrógeno; 2010

Sewage sludge has been used as N fertilizer because it contains some of inorganic N, mainly as nitrate and ammonium ions. However, sewage sludge addition to legumes could result in impaired nodule metabolism due to the presence of inorganic N from sludge. A greenhouse experiment was conducted to examine the effects of sewage sludge on growth, photosynthesis, nitrogen assimilation and nodule metabolism in alfalfa plants. The experiment included three treatments: (1) plants inoculated with rhizobia and amended with sewage sludge at rate of 10% (w/w) (RS); (2) plants inoculated with rhizobia without any amendment (R); and (3) non-inoculated plants fed with ammonium nitrate (N). N2-fixing plants had lower growth but higher photosynthesis than nitratefed plants. Sewage sludge-treated plants evidenced lower photosynthetic capacity and N2 fixation efficiency than untreated plants. Besides, sewage sludge addition did no affect nodulation but induced a decrease in nodule enzyme activities involved in carbon and N metabolisms that may lead to accumulation of toxic N-compounds.