Uptake and Assimilation of NO₃⁻ and NH₄⁺ by Nitrogen-Deficient Perennial Ryegrass Turf

Abstract

Assimilation of NO3-and NHI' by perennial ryegrass (Lolium perenne L.) turf, previously deprived of N for 7 days, was examined. Nitrogen uptake rate was increased up to four-to five-fold for both forms of N by N-deprivation as compared to N-sufficient controls, with the deficiencyenhanced N absorption persisting through a 48 hour uptake period.Nitrate, but not NH4R, accumulated in the roots and to a lesser degree in shoots. By 48 hours, 53% of the absorbed NO3-had been reduced, whereas 97% of the NH4 had been assimilated. During the early stages (O to 8 hours) of N03 uptake by N-deficient turf, reduction occurred primarily in the roots. Between 8 and 16 hours, however, the site of reduction shifted to the shoots. Nitrogen form did not affect partitio ing of the absorbed N between roots (40%) and shoots (60%) but did affect growth. Compared to N03-, NH.g uptake inhibited root, but not shoot, growth. Total soluble carbohydrates decreased in both roots and shoots during the uptake period, principally the result of fructan metabolism. Ammonium uptake resulted in greater total depletion of soluble carbohydrates in the root compared to N03-uptake. The data indicate that N assimilation by ryegrass turf utilizes stored sugars but is also dependent on current photosynthate.Nitrogen deficiency enhances N uptake by turfgrasses (3,4) as well as other crop plants (1,20). Periods ofN deprivation, ranging in duration from 1 to 4 weeks (3) to as short as 4 h (4), increased the uptake of both N03 -N and NH4+-N by mature perennial ryegrass turf. Nitrogen equivalent to a normal 50 kg N ha-' application (approximately 1 lb N/1000 ft2) was absorbed in 2 d or less (3), and it was suggested that such rapid N absorption might be the principal cause of the short-lived growth response typically observed with turf following application of inorganic N fertilizers. Implicit in this suggestion is that the absorbed N is also rapidly assimilated. The literature contains numerous reports on NO3-assimilation by N-deficient graminaceous plants (7,8,12,17,23), which describe a pattern of accumulation, reduction, and translocation. Other studies (21, 22) have revealed the dominant role of shoots in the assimilation of NO3-and roots in assimilation ofNH4'. However, there are no comparable data for mowed turf systems recovering from N deficiency.In addition to increasing N uptake, nitrogen deprivation results in accumulation of soluble carbohydrates in roots, both in perennial ryegrass (4,29) and other species (7,17,28). High levels of carbohydrates may be involved both in the uptake and assimilation ofN (1,13,17,28) (13,17,28). It is apparently not known which of the various sugars in root systems are specifically involved in assimilation, although glucose preferentially stimulated both uptake and reduction of NO3-by dwarf bean (13).This paper presents results of an investigation into the assimilation ofboth NO3-and NH4' by N-deficient perennial ryegrass turf. Whereas N assimilation has typically been studied with seedlings or excised plant ...

Kinetics of NH4+ Influx in Spruce

“…This finding is in agreement with several other studies in higher-plant species (Ivanko and Ingversen, 1971;Lee and Rudge, 1986;Morgan andJackson 1988a, 1988b;Henriksen et al, 1992;Jackson and Volk, 1992;Mack and Tischner, 1994). Typically, initial fluxes are in the order of 2 to 3 times steady rates (Bowman et al, 1988;Lee et al, 1992). Similar responses have been documented for potassium, phosphate, sulfate, chloride, and bromide when plants were deprived of these ions (cf.…”

Mineral Nitrogen in Plant Physiology and Plant Nutrition

“…'~~J~~.~~~ Because NH, assimilation basically occurs in mots, and as NH, assimilation requires large amounts of carbohydrates, there is a decrease in root growth rates in plants grown under NH, n~t r i t i o n .~~.~ When the N supply to ryegrass roots in nutrient solution was suppressed for 7 d, root weight increased by 24%, while leaf weight was simultaneously reduced by 24%. 27 This reduction in shoot weight was attributed to the diversion of carbohydrates used in the assimilation of N since it takes five glucose equivalents for the fixation of eight N equivalents. There is a drastic reduction in corn root weight as NH, levels increase in the nutrient solution ( the soil solution reaches higher levels.…”

Relationships between shoot to root ratio, growth and leaf soluble protein concentration of Pisum sativum, Phaseolus vulgaris and Triticum aestivum under different nutrient deficiencies

“…There are several reports that at similar total plant DW, S : R is greater with NH 4 + than with NO 3 -as N source (Cox & Reisenhauer 1973;Timpo & Neyra 1983;Bowman & Paul 1988;Troelstra, Wagenaar & Smant 1992). However, where tested in these studies, the tissue N concentration for plants of similar DW was also greater with NH 4 + than with NO 3 -.…”