Background Plantlets grown in vitro with a mixed nitrogen source utilize sucrose and CO2 as carbon sources for growth. However, it is very difficult to obtain the correct utilization proportions of nitrate, ammonium, sucrose and CO2 for plantlets. Consequently, the biological effect of ammonium/nitrate utilization, the biological effect of sucrose/CO2 utilization, and the ammonium/nitrate use efficiency for new C input derived from CO2 assimilation/sucrose utilization are still unclear for plantlets. Results The bidirectional stable nitrogen isotope tracer technique quantified the proportions of assimilated nitrate and ammonium in Brassica napus plantlets grown at different ammonium/nitrate ratios. The utilization proportions of sucrose and CO2 could be quantified by a two end-member isotope mixing model for Bn plantlets grown at different ammonium/nitrate ratios. Under the condition that each treatment contained 20 mM ammonium, the proportion of assimilated nitrate did not show a linear increase with increasing nitrate concentration for Bn plantlets. Moreover, the proportion of assimilated CO2 did not show a linear relationship with the nitrate concentration for Bn plantlets. Increasing the nitrate concentration contributed to promoting the assimilation of ammonium and markedly enhanced the ammonium utilization coefficient for Bn plantlets. With increasing nitrate concentration, the amount of nitrogen in leaves derived from nitrate assimilation increased gradually, while the nitrate utilization coefficient underwent no distinct change for Bn plantlets. Conclusions Quantifying the utilization proportions of nitrate and ammonium can reveal the energy efficiency for N assimilation in plantlets grown in mixed N sources. Quantifying the utilization proportion of CO2 contributes to evaluating the photosynthetic capacity of plantlets grown with variable ammonium/nitrate ratios. Quantifying the utilization proportions of nitrate, ammonium, sucrose and CO2 can reveal the difference in the ammonium/nitrate use efficiency for new C input derived from CO2 assimilation/sucrose utilization for plantlets grown at variable ammonium/nitrate ratios.

Poor growth is often observed in artificial young forests due to insufficient inorganic nitrogen in karst soils. However, little is known about the assimilatory demand of the whole plant for nitrate and the partitioning of nitrate assimilation in roots and leaves in woody plants grown in karst habitats. In this study, Broussonetia papyrifera (L.) Vent (B. papyrifera) seedlings were grown under nearly hydroponic conditions. The isotope mass balance approach was employed to quantify the δ15N values of the N assimilates in plant organs and in whole plants for B. papyrifera seedlings grown at different nitrate concentrations. The δ15N values of the N assimilates in the whole B. papyrifera seedlings showed a rising trend with increasing nitrate concentration. Increasing the supply of nitrate decreased the leaf–root difference in the δ15N values of the N assimilates for B. papyrifera seedlings. Quantifying the δ15N values of N assimilates in the whole B. papyrifera seedlings grown under different nitrate concentrations contributes to estimating the assimilatory demand of the B. papyrifera seedlings for nitrate. The leaf–root difference in the δ15N values of the N assimilates can be used to estimate the partitioning of nitrate assimilation in the roots and leaves.

Turbine blades made of Ni‐based single crystal superalloys (NBSXs) have long‐strip shaped cross sections and rectangular‐sectional structures, where the secondary orientation produces potential effects even the primary orientation is fixed at [001]. Low cycle fatigue behaviors between [010] and [110] transversely oriented rectangular‐sectional NBSX specimens were compared. Obvious differences existed under 600°C but disappeared under 850°C, with the deformation mechanism and fracture mode transitions. Secondary orientation effects on stress asymmetry and fatigue life cannot be described by the conventional LCP model and critical plane method but were well explained by dislocation path length‐dependent back‐stress model and A.N. May's random slip model.

No abstract

BackgroundPlantlets grown in vitro with a mixed nitrogen source utilize sucrose and CO2 as carbon sources for growth. However, it is very difficult to obtain the correct proportion of assimilated nitrate, ammonium, sucrose and CO2 for plantlets. Consequently, the NH4+/NO3- use efficiency for carbon fixation derived from the assimilation of sucrose/CO2 is still unclear for plantlets. ResultsThe bidirectional stable nitrogen isotope tracer technique was employed to quantify the proportions of nitrate and ammonium utilized at different NH4+/ NO3- ratios, and the proportions of sucrose and CO2 assimilation were quantified by the foliar δ13C values of plantlets. There was an obvious difference in the assimilation of nitrate and ammonium under different NH4+/NO3- ratios for Brassica napus (Bn) plantlets. Increasing the supply of nitrate contributed to enhancing the assimilation of nitrate and ammonium simultaneously. The nitrate utilization coefficients of the Bn plantlets had no distinct change with increasing nitrate concentration, while the ammonium utilization coefficients of the Bn plantlets increased obviously with increasing nitrate concentration. The proportion of sucrose/CO2 assimilation depended on the NH4+/NO3- ratios of the Bn plantlets. Both nitrate and ammonium assimilation were independent of sucrose/CO2 assimilation. Based on the proportion of CO2, sucrose, nitrate and ammonium utilization, the nitrate/ammonium use efficiency (as indicated by the C/N ratio) for carbon fixation derived from the assimilation of sucrose/CO2 can be quantified for Bn plantlets.ConclusionsQuantifying the utilization proportions of nitrate and ammonium can reveal the difference in nitrate and ammonium utilization among plantlets at different NH4+/NO3- ratios. Foliar δ13C value in combination of the foliar δ15N value of plantlets can be used to quantify the nitrate/ammonium use efficiency for the carbon fixation derived from the assimilation of sucrose/CO2, which contributes to knowing the coupling process of carbon and nitrogen in plantlets and provides an alternate way to optimize the supply of inorganic nitrogen in culture media.