Finnigan delta 5 advantage

Nitrogen stable isotope ratio was determined using an elemental analyzer (Flash EA 1112HT, Thermo Fisher Scientific, Inc., United States) coupled with an isotope ratio mass spectrometer (Finnigan Delta V Advantage, Thermo Fisher Scientific, Inc.). The total content of ¹⁵N in a specific organ type (leaf, stem, or root) was calculated as the product of DW and the ¹⁵N concentration of each organ type. Over the 20 days stress period, the ¹⁵N uptake flux was calculated based on the RGR, DW, and total contents of ¹⁵N in the root, stem, and leaf according to the equation of Liang et al. (2017) (link). Partitioning among leaves, stems, and roots was examined relative to the whole-plant contents of ¹⁵N.

The isotopic compositions were analyzed using an elemental analyzer (Flash EA 1112Ht, Thermo Fisher Scientific, Inc., San Diego, CA, USA) coupled with an isotope-ratio mass spectrometer (Finnigan Delta V Advantage, Thermo Fisher Scientific, Inc.). Stable isotope ratios are expressed in δ (‰) notation with respect to Pee Dee Belemnite (PDB) for δ¹³C and atmospheric N₂ for δ¹⁵N
$\mathrm{\delta }\mathrm{X}\left(\mathrm{‰}\right)=\left[\left({\mathrm{R}}_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}/{\mathrm{R}}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{a}\mathrm{r}\mathrm{d}}\right)-1\right]\times {10}^3$
where X is either ¹³C or ¹⁵N, R_sample is the ¹³C/¹²C or ¹⁵N/¹⁴N isotope ratio in the sample and R_standard is the ¹³C/¹²C or ¹⁵N/¹⁴N isotope ratio for the standard. An internal standard (glycine) was run for every twelve samples. Measurement precision was 0.1 ‰ and 0.2 ‰ for δ¹³C and δ¹⁵N values, respectively.