Fig 1.
Illustration of the experimental design.
Six manipulative steps are shown along the experiment timeline: 1) seeds germination at d 0; 2) potting at d 5; 3) labelling with ammonium nitrate solution, including 3 treatments (T, each on 30 replicated pots) with the same isotopic ratio, i.e. δ15NAir-N2 = 2100 mUr, but differing by the labelled chemical species (ṄH4, ṄO3 or ṄH4ṄO3), plus the untreated control (C, 10 replicates) administered with the same dose of unlabelled ammonium nitrate (N); 4) destructive sampling (6 replicates per treatment at each of 5 observation stages from d 60 to d 120) and separation of leaf, stem and root materials (L, S and R, respectively); 5) DNA extraction and purification from leaf ad root materials; 6) CHN-IRMS analysis of dry aliquots of plant materials and corresponding DNA samples. See methods for further details.
Fig 2.
Dynamics of dry biomass and percent N content in B. napus leaves, stems and roots of plants grown for 120 days in controlled conditions and fertilized with ammonium nitrate according to different N isotopic labelling treatments differing by the labelled chemical species (ṄH4, ṄO3, or both) but with the same isotopic ratio (δ15NAir-N2 = 2100 mUr).
Arrows on the left panels indicate the labelling administration date at plant age of 10 d. Data refer to mean of 6 plants for each treatment combination. Deviation bars are omitted to improve readability. Statistical support in S2, S3 and S4 Tables.
Fig 3.
Dynamics of N isotopic composition in B. napus leaves and roots (left) and DNA samples extracted therefrom (center) across the labelling treatments.
Right panels show the corresponding δ 15N Normalized Difference Index (NDI) dynamics. Data refer to mean of 6 plants for each treatment combination. Statistical support in Tables 1 and 2, and S8, S9 and S10 Tables.
Table 1.
Results of GLM for δ 15N of plant materials and DNA extracted thereof.
Table 2.
Results of GLM for δ 15N NDI.