Aims
Subtropical ecosystems are generally characterized by phosphorus (P)-deficient soils; however, extreme P-rich soils develop on phosphate rocks. We aimed to integrate metabolomic and ionomic analyses to survey how in situ trees adaptively respond to such contrasting P soils.

Methods
Gas (GC-MS) or liquid (LC-MS) chromatography-mass spectrometry and inductively coupled plasma-optical emission spectrometer (ICP-OES) were used to analyze leaf metabolome and ionome of Quercus variabilis, which grew at two geologic P-rich and P-deficient sites in subtropical China.

Results
Two Q. variabilis populations were significantly discriminated in terms of metabolome and ionome, with major contributions from 25 identified metabolites (e.g. sugars and P-containing compounds) and P and four other chemical elements. And of these 25 metabolites, orthophosphate was predominant in influencing the variation in the metabolomes of Q. variabilis between the two P-type sites. Moreover, orthophosphate was correlated with leaf P (r = 0.85, p < 0.001), while leaf P was significantly influenced only by soil resident P at the P-rich site. Furthermore, the metabolic pathway analysis indicated four critical metabolic pathways: galactose metabolism, amino sugar and nucleotide sugar metabolism, glyoxylate and dicarboxylate metabolism, fructose and mannose metabolism.

Conclusions
These findings suggested that there were distinct ionome-metabolome interactions in Q. variabilis populations, between P-rich and P-deficient sites, which contributed to novel insights into how plants interactively adapt to P-limiting soils.