Quantifying remobilization of pre-existing nitrogen from cuttings to new growth of woody plants using 15N at natural abundance

Plant Methods

Robert D Guy¹  Lee A Kalcsits¹ 

[1] Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T1Z4, Canada

关键词: δ¹⁵N;    Poplar;    Nitrogen remobilization;   

Others  :  820327
DOI  :  10.1186/1746-4811-9-27

 received in 2013-02-25, accepted in 2013-07-01,  发布年份 2013

【 摘 要 】

Background

For measurements of nitrogen isotope composition at natural abundance, carry-over of pre-existing nitrogen remobilized to new plant growth can cause deviation of measured isotope composition (δ¹⁵N) from the δ¹⁵Nof newly acquired nitrogen. To account for this problem, a two-step approach was proposed to quantify and correct for remobilized nitrogen from vegetative cuttings of Populus balsamifera L. grown with either nitrate (δ¹⁵N = 58.5‰) or ammonium (δ¹⁵N = −0.96‰). First, the fraction of carry-over nitrogen remaining in the cutting was estimated by isotope mass balance. Then measured δ¹⁵N values were adjusted for the fraction of pre-existing nitrogen remobilized to the plant.

Results

Mean plant δ¹⁵N prior to correction was 49‰ and −5.8‰ under nitrate and ammonium, respectively. Plant δ¹⁵N was non-linearly correlated to biomass (r² = 0.331 and 0.249 for nitrate and ammonium, respectively; P < 0.05) where the δ¹⁵N of plants with low biomass approached the δ¹⁵N of the pre-existing nitrogen. Approximately 50% of cutting nitrogen was not remobilized, irrespective of size. The proportion of carry-over nitrogen in new growth was not different between sources but ranged from less than 1% to 21% and was dependent on plant biomass and, to a lesser degree, the size of the cutting. The δ¹⁵N of newly acquired nitrogen averaged 52.7‰ and −6.4‰ for nitrate and ammonium-grown plants, respectively; both lower than their source values, as expected. Since there was a greater difference in δ¹⁵N between the carried-over pre-existing and newly assimilated nitrogen where nitrate was the source, the difference between measured δ¹⁵N and adjusted δ¹⁵N was also greater. There was no significant relationship between biomass and plant δ¹⁵N with either ammonium or nitrate after adjusting for carry-over nitrogen.

Conclusion

Here, we provide evidence of remobilized pre-existing nitrogen influencing δ¹⁵N of new growth of P. balsamifera L. A simple, though approximate, correction is proposed that can account for the remobilized fraction in the plant. With careful sampling to quantify pre-existing nitrogen, this method can more accurately determine changes in nitrogen isotope discrimination in plants.

【 授权许可】

   
2013 Kalcsits and Guy; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

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