Data analysis
Metabolite and lipid identification were based on retention indices and total similarity scores found within MSDIAL, version 3.82 (Tsugawa et al., 2015). Compounds were normalized relative to the internal standard. An in-house custom library augmented with a library from Riken database (http://prime.psc.riken.jp/Metabolomics_Software/MSDIAL/index.html) was used for spectral matching of polar metabolites. To test metabolite profile difference between treatments, metabolite abundance were Hellinger-transformed (Ramette, 2007) and principal component analysis (PCA) was performed with PC-ORD v6.08 (McCune & Mefford, 1999).
Data on plant biomass, root system architecture (primary seminal root length, total root length, root surface area), ion content, lipid and metabolite abundance were subjected to statistical analysis by one-way ANOVA, using JMP software (SAS institute Inc., Cary, NC, USA). Significance was defined as a probability level of P ≤0.05. Total root length and root surface area were determined using WinRHIZO software (Regent Instruments Inc., Ontario, CA).