Potential organic and inorganic N uptake by six Eucalyptus species

2006 ◽  
Vol 33 (7) ◽  
pp. 653 ◽  
Author(s):  
C. R. Warren

There are no published studies of organic N uptake by species of south-eastern Australia (e.g. Eucalyptus) despite several studies of ecosystem N cycling. This study examines uptake of nitrate, ammonium and glycine (an amino acid) by six species of 16-year-old Eucalyptus growing at two plantations (‘common gardens’). By using two plantations, one xeric / oligotrophic and one mesic / eutrophic, I was able to disentangle genotypic from phenotypic differences in preference for N forms. Measurements were made on three separate occasions during spring. N uptake was examined in situ with attached roots placed in uptake solutions containing equimolar 100 μmol L–1 concentrations of 15N-nitrate, 15N-ammonium and 2-13C215N-glycine. Water and KCl extracts were used to determine the relative abundances of nitrate, ammonium and amino acids at the two plantations. Nitrate dominated at the eutrophic site, but was nearly absent at the oligotrophic site. N at the oligotrophic site was dominated by ammonium and amino acids which were present in similar concentrations. The rate of uptake of ammonium (6.3 ± 0.4 μmol g h–1; mean ± s.e., n = 108), was faster than glycine (3.4 ± 0.2), which was faster than nitrate (0.62 ± 0.07). Plant ‘preference’ for N forms did not vary between sites despite large differences in the relative abundances of N forms (nitrate v. ammonium v. amino acids). Hence, there was little evidence for acclimation of Eucalyptus species to differences in the relative availability of N forms. This study suggests the possibility for considerable organic N uptake in the field. Previous studies of ecosystem N cycling in south-eastern Australia have only examined inorganic N. The N cycle in south-eastern Australia needs to be revisited with a new perspective, one that considers inorganic N and organic N.

2011 ◽  
Vol 8 (6) ◽  
pp. 11311-11335 ◽  
Author(s):  
E. Gioseffi ◽  
A. de Neergaard ◽  
J. K. Schjoerring

Abstract. Soil-borne amino acids may constitute a nitrogen (N) source for plants in various terrestrial ecosystems but their importance for total N nutrition is unclear, particularly in nutrient-rich arable soils. One reason for this uncertainty is lack of information on how the absorption of amino acids by plant roots is affected by the simultaneous presence of inorganic N forms. The objective of the present study was to study absorption of glycine (Gly) and glutamine (Gln) by wheat roots and their interactions with nitrate (NO3–) and (NH4+) during uptake. The underlying hypothesis was that amino acids, when present in nutrient solution together with inorganic N, may lead to down-regulation of the inorganic N uptake. Amino acids were enriched with double-labelled 15N and 13C, while NO3– and NH4+ acquisition was determined by their rate of removal from the nutrient solution surrounding the roots. The uptake rates of NO3– and NH4+ did not differ from each other and were about twice as high as the uptake rate of organic N when the different N forms were supplied separately in concentrations of 2 mM. Nevertheless, replacement of 50 % of the inorganic N with organic N was able to restore the N uptake to the same level as that in the presence of only inorganic N. Co-provision of NO3– did not affect glycine uptake, while the presence of glycine down-regulated NO3– uptake. The ratio between 13C and 15N were lower in shoots than in roots and also lower than the theoretical values, reflecting higher C losses via respiratory processes compared to N losses. It is concluded that organic N can constitute a significant N-source for wheat plants and that there is an interaction between the uptake of inorganic and organic nitrogen.


2012 ◽  
Vol 9 (4) ◽  
pp. 1509-1518 ◽  
Author(s):  
E. Gioseffi ◽  
A. de Neergaard ◽  
J. K. Schjoerring

Abstract. Soil-borne amino acids may constitute a source of nitrogen (N) for plants in various terrestrial ecosystems but their importance for total N nutrition is unclear, particularly in nutrient-rich arable soils. One reason for this uncertainty is lack of information on how the absorption of amino acids by plant roots is affected by the simultaneous presence of inorganic N forms. The objective of the present study was to study absorption of glycine (Gly) and glutamine (Gln) by wheat roots and their interactions with nitrate (NO3−) and ammonium (NH4+) during uptake. The underlying hypothesis was that amino acids, when present in nutrient solution together with inorganic N, may lead to down-regulation of the inorganic N uptake, thereby resulting in similar total N uptake rates. Amino acids were enriched with double-labelled 15N and 13C, while NO3− and NH4+ acquisition was determined by their rate of removal from the nutrient solution surrounding the roots. The uptake rates of NO3− and NH4+ did not differ from each other and were generally about twice as high as the uptake rate of organic N when the different N forms were supplied separately in concentrations of 2 mM. Nevertheless, replacement of 50% of the inorganic N with organic N was able to restore the N uptake to the same level as that in the presence of only inorganic N. Co-provision of NO3− did not affect glycine uptake, while the presence of glycine down-regulated NO3− uptake. The ratio between 13C and 15N were lower in shoots than in roots and also lower than the theoretical values, reflecting higher C losses via respiratory processes compared to N losses. It is concluded that organic N can constitute a significant N-source for wheat plants and that there is an interaction between the uptake of inorganic and organic N.


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