AUTHOR=de Oliveira Silva Amanda , Camberato James J. , Coram Tristan , Filley Timothy , Vyn Tony J. TITLE=Applicability of a “Multi-Stage Pulse Labeling” 15N Approach to Phenotype N Dynamics in Maize Plant Components during the Growing Season JOURNAL=Frontiers in Plant Science VOLUME=8 YEAR=2017 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01360 DOI=10.3389/fpls.2017.01360 ISSN=1664-462X ABSTRACT=

Highlights

This work utilizes “multi-stage pulse labeling” ¹⁵N applications, primarily during reproductive growth stages, as a phenotyping strategy to identify maize hybrids with superior N use efficiency (NUE) under low N conditions.

Research using labeled isotopic N (¹⁵N) can precisely quantify fertilizer nitrogen (N) uptake and organ-specific N allocation in field crops such as maize (Zea mays L.). The overall research objective was to study plant N uptake patterns potentially correlated with N use efficiency (NUE) in field-grown maize hybrids using a “multi-stage pulse labeling” ¹⁵N phenotyping strategy with an emphasis on the reproductive period. Five hybrids varying in NUE were compared under zero N fertilizer application (0N) plus a moderate rate of 112 kg N ha⁻¹ (112N) in 2013 (2 locations) and 2014 growing seasons. The equivalent of 3.2 (2013) to 2.1 (2014) kg of ¹⁵N ha⁻¹, as labeled Ca(¹⁵NO₃)₂, was injected into soil on both sides of consecutive plants at multiple stages between V14 and R5. Aboveground plant biomass was primarily collected in short-term intervals (4–6 days after each ¹⁵N application) in both years, and following a single long-term interval (at R6 after ¹⁵N injection at R1) in 2014. Averaged across hybrids and site-years, the moderate N rate (112N) increased absolute ¹⁵N uptake at all stages; however, plants in the 0N treatment allocated proportionally more ¹⁵N to reproductive organs. Before flowering, short-term recovery of ¹⁵N (¹⁵Nrec) totaled ~0.30 or 0.40 kg kg⁻¹ of the ¹⁵N applied, and ~50% of that accumulated ¹⁵Nu was found in leaves and 40% in stems. After flowering, plant ¹⁵Nrec totaled ~0.30 kg kg⁻¹ of ¹⁵N applied, and an average 30% of accumulated ¹⁵Nu was present in leaves, 17% in stems, and the remainder—usually the majority—in ears. At the R5 stage, despite a declining overall rate of ¹⁵N uptake per GDD thermal unit, plant ¹⁵Nrec represented ~0.25 kg kg⁻¹ of ¹⁵N applied, of which ~65% was allocated to kernels. Overall long-term ¹⁵Nrec during grain filling was ~0.45 and 0.70 kg kg⁻¹ of total ¹⁵N applied at R1 with 0 and 112N, respectively, and most (~77%) ¹⁵N uptake was found in kernels. The “multi-stage pulse labeling” technique proved to be a robust phenotyping strategy to differentiate reproductive-stage N uptake/allocation patterns to plant organs and maize efficiencies with newly available fertilizer N.