Ionic balance, biomass production, and organic nitrogen as affected by salinity and nitrogen source in annual ryegrass

Abstract

Studies on the effects of salinity and nitrogen (N) fertilization on ionic balance, biomass, and organic N production of annual ryegrass (Lolium multiflorum Lam.) were conducted. Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS#lbm^‐1, and N in the form of sodium nitrate (NaNO₃), ammonium nitrate (NH₄NO₃), or ammonium sulfate [(NH₄)₂SO₄] ranging from 0.5 to 9.0 mM. Salinity increased the concentration of total inorganic cations (C) in plants and specifically sodium (Na) by more than 3‐fold higher in plants grown at high salinity as compared with plants at low salinity. Sodium (Na) concentration in roots was higher than in shoots irrespective of the salinity level, suggesting a restriction of Na transport from roots to shoots. The concentration of total inorganic anions (A) increased with salinity and when plants were supplied with nitrate (NO₃), salinity increased the concentrations of NO₃ and chloride (Cl) in plants. Increasing salinity and N concentration in the growth medium increased organic anions concentration in plants, estimated as the difference between C and A. The effect of different N sources on C‐A followed the order: NH₄NO₃ > NO₃ > ammonium (NH₄). The base of organic anions and inorganic ions with salinity contributed significantly to the osmotic potential of plants shoots and roots. Changes in C affected N and organic acids metabolism in plants, since C were highly correlated (p=0.0001) with C‐A and organic N (N_org) concentrations regardless of the salinity level or N source in the nutrient solutions. A high and positive linear dependency was found between N_org and C‐A in plants grown at high and low salinity levels and different N sources, pointing out the close relationship between N_org and organic anions on metabolism under these conditions. The amount of biomass produced was correlated positively with organic anion concentration in plants exposed to different salinity levels. Plant biomass increased with N concentration in the nutrient solution regardless of the salinity level applied. Biomass accumulation decreased while N_org concentration increased with salinity. Organic N content remained unaffected in plants exposed to salinity when grown in N less than 9.0 mM.