Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning

Abstract

The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO $ − ), ammonium (NH % + ) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot-root biomass allocation were evaluated. The results indicated that NO $ − as an N source for plant growth is not substantially more expensive to utilize than either NH % + or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot-root biomass allocation.

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

“…For this to be the case, C utilization in processing N must be of a magnitude which could affect dry matter partitioning between shoot and root. There is general agreement that for higher plants usually 25-65% of C fixed in photosynthesis is lost via respiration (Byrd, Sage & Brown 1992;Amthor 1994;Zerihun et al 1998). Zerihun et al (1998) calculated the photosynthetic costs associated with the utilization of NO 3 -, NH 4 + or glutamine as N source and concluded that costs were similar with the different N forms particularly in the longer term when costs due to turnover of protein (primarily soluble protein) dominate the total cost of N utilization.…”

“…There is general agreement that for higher plants usually 25-65% of C fixed in photosynthesis is lost via respiration (Byrd, Sage & Brown 1992;Amthor 1994;Zerihun et al 1998). Zerihun et al (1998) calculated the photosynthetic costs associated with the utilization of NO 3 -, NH 4 + or glutamine as N source and concluded that costs were similar with the different N forms particularly in the longer term when costs due to turnover of protein (primarily soluble protein) dominate the total cost of N utilization. It has been estimated that 25-60% of total respiratory loss is due to protein turnover (Penning de Vries 1975;Barneix et al 1988; de Visser, Spitter & Bouma 1992).…”

“…The increase in organic N concentration is likely to be due to increases in a range of N-containing molecules but mainly amino acids and proteins. Soluble protein is likely to be of particular importance as it usually constitutes around 50% of total N in leaves although insoluble protein is likely to increase in parallel with soluble protein and also constitute a substantial fraction of organic N (Evans 1989;Anderson et al 1997;Zerihun, McKenzie & Morton 1998). Nitrate uptake, NO 3 -assimilation and protein synthesis are energy-requiring processes hence the increase in organic N concentration reflects an increased proportion of energy/C derived from photosynthesis being utilized in processing NO 3 -.…”

Analysis of Nitrogen Utilization Capability during the Proliferation and Maturation Phases of Norway Spruce (Picea abies (L.) H.Karst.) Somatic Embryogenesis

“…Embryogenic cultures grown without L-glutamine must synthesize this amino acid from the nitrogen sources available in the medium. This can be seen as an energetic disadvantage in comparison to PEM cultures which can take up the L-glutamine directly from the medium [25,26], although energy is not a limiting factor if sucrose is supplied in the medium. The beneficial effect of L-glutamine on growth of cell cultures has been shown for several conifer species including Pseudotsuga menziesii (Mirb.)…”

Carbon Assimilation, Biomass Partitioning and Productivity in Grasses

“…However, the N form is rarely considered. Zerihun et al [73] noted that there are significantly different C costs associated with assimilating nitrate, ammonium, or glutamine, and that the physical location and time of assimilation could also have effects. For example, malate derived from photorespiration acts as a source of reducing power for nitrate, where assimilation occurs in the leaves during the light period, without significantly affecting carbon fixation rates [23].…”