Uptake and assimilation of nitrate and ammonium by nitrogen-deficient perennial ryegrass turf

The uptake and assimilation of NO;Stimulation of N uptake was apparent after only 4 hr and reached a maximum after 2 to 3 days of N-stress. This response was not related to changes in growth, total soluble carbohydrate levels, or specific sugars in the tissue. Carbohydrates, however, did accumulate in leaves, shoots and roots, mainly as sucrose and fructans, over a 7 day period of N deprivation. The data suggest that enhanced N uptake may be controlled allosterically by tissue (NO;Assimilation of NO;Accumulated carbohydrates in root and shoot tissue were depleted rapidly and to a similar degree during uptake and assimilation of both N forms, due mainly to fructan metabolism (although some sucrose metabolism was indicated). Ammonium assimilation nearly depleted root carbohydrates while NO;These results support the observation that N absorption by N-deficient turf in the field is very rapid, and may explain why the growth response to inorganic N fertilizers is typically short-lived.