The sensitivity to ammonium nutrition is related to nitrogen accumulation

Ammonium and NO3- can be utilized as nitrogen sources by most plant species although the plant response to continuous ammonium nutrition is species dependent. The effect of the nitrogen source (nitrate and ammonium) on growth, photosynthetic parameters and nitrogen content in spinach (Spinacea oleracea L.), sunflower (Helianthus annuus L.) and pea (Pisum sativum L.) was studied. Results showed spinach to be highly sensitive, sunflower moderately sensitive and pea tolerant to ammonium nutrition. Ammonium accumulation in shoots was closely correlated to growth reduction. Moreover, ammonium accumulation was correlated to an increase of organic nitrogen content. The data suggest that the site of ammonium assimilation is a key factor controlling tolerance to ammonium nutrition in the different plant species. with plants being more tolerant when ammonium is assimilated in roots. (C) 2001 Elsevier Science B.V. All rights reserved.