Influence of N form on growth and water status of tomato plants

Abstract

A greenhouse experiment with tomato plants (cv. Daniella) was carried out in order to characterise the interaction between different N forms and the water availability. Since several indicators suggested that ammonium supply results in impaired water status the effect of Cl as an inorganic osmolyte replacing the osmotic function of NO₃ was tested. NH₄ supply resulted in reduced leaf area and impaired shoot growth, while root weight ratio (RWR) was increased. Among the plants grown with 100% NH₄, those without Cl showed a higher RWR at low water supply (as did the nitrate-grown plants) while those receiving 10 mM Cl showed the inverse response. Concerning the water status of the leaves, the water content was reduced by NH₄ supply, but it tended to be increased by Cl supply at low water availability only. However, transpiration rate based on leaf area was significantly increased by NH₄ supply, particularly when Cl was provided. All this indicates that the water status on the tissue level are impaired in NH₄-grown plants, which is also supported by the higher osmolyte and water contents when Cl was provided.