Applicability of a “multi-stage pulse labeling” 15N approach to phenotype n dynamics in maize plant components during the growing season

Abstract

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”15 N 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 112kg Nha−1 (112N) in 2013 (2 locations) and 2014 growing seasons. The equivalent of 3.2 (2013) to 2.1 (2014) kg of15 N 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 each15N application) in both years, and following a single long-term interval (at R6 after15N injection at R1) in 2014. Averaged across hybrids and site-years, the moderate N rate (112N) increased absolute15 N uptake at all stages; however, plants in the 0N treatment allocated proportionally more15 N to reproductive organs. Before flowering, short-term recovery of15N (15 Nrec) totaled ∼0.30 or 0.40kg kg−1 of the15 N applied, and ∼50% of that accumulated15Nu was found in leaves and 40% in stems. After flowering, plant15 Nrec totaled ∼0.30kg kg−1 of15 Napplied, and an average 30%of accumulated15 Nu was present in leaves, 17% in stems, and the remainder—usually the majority—in ears. At the R5 stage, despite a declining overall rate of15N uptake per GDD thermal unit, plant15 Nrec represented ∼0.25kg kg−1 of15 N applied, of which ∼65% was allocated to kernels. Overall long-term15 Nrec during grain filling was ∼0.45 and 0.70kg kg−1 of total15 N 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.