Effects of Nitrogen Deficiency on Photosynthesis and Chlorophyll a Fluorescence Attributes at Two Contrasting Legume Forages

Abstract

Exploration of genetic resources constitutes an eminent device for the selection of interesting tolerant forage species for nitrogen deficiency. In this regard, the performance of two legume forage species (Sulla carnosa (Desf.) B.H.Choi & H.Ohashi, wild halophytic species; Trifolium alexandrinum L., commercially cultivated species) to nitrogen deficiency was compared on the basis of the total dry weight, relative growth rate, nitrogen accumulation, nitrogen use efficiency, photosynthetic activity and chlorophyll a fluorescence. Plants were supplied with mixed nitrogen form (NO3NH4) at a concentration of 5.0 mM (NS–nitrogen sufficient) or 0.5 mM (ND–nitrogen deficiency) and cultivated under hydroponic controlled conditions. At S. carnosa, nitrogen deficiency reduced growth rate (68%), nitrogen use efficiency (16%), net photosynthetic assimilation rate (36%), maximum photochemical efficiency of PSII (7%), PSII operating efficiency (19%), photochemical quenching coefficient (8%) and non-cyclic electron transport rate (19%), while it had no deleterious effects on growth, photosynthesis and PSII photochemistry at T. alexandrinum. The data in the present research clearly indicated that S. carnosa was more sensitive to nitrogen deficiency than T. alexandrinum, which was mainly related to decline of NUE and to the damage of the photosynthetic apparatus and consequently to the decline of the photosynthetic activity. Despite its sensitivity, S. carnosa had the ability to use nitrogen more efficiently (27%) and to produce a biomass comparable to that of the cultivated legume species T. alexandrinum.