Imbalanced plant stoichiometry at contrasting geologic-derived phosphorus sites in subtropics: the role of microelements and plant functional group

Subtropical soils are generally characterized as deficient in phosphorus (P), calcium (Ca) and magnesium (Mg), but rich in iron (Fe) and aluminum (Al). However, soils developed in phosphate rock are extremely P-rich in subtropical forests, southwestern China. Factors controlling plant stoichiometric traits across variable P sites are still not clear. We investigated leaf macroelements (C, N, P, K, Ca and Mg), microelements (Mn, Fe, Zn, and Cu), and non-essential elements (Na and Al) and their element:P ratios for 21 woody plant species at both P-rich and P-deficient sites. Plants between the two P type sites were mainly discriminated by Mn, Al, N and their P ratios, and between functional groups by Cu, Fe, Zn and their P ratios. There were higher leaf N, P, K, Ca, Fe and Zn concentrations but lower Mn, Cu and Al at the P-rich sites. Evergreen conifers displayed strict homeostasis while evergreen and deciduous broadleaf were more plastic and had variable ratios across different nutrients. Microelements have strong influences on plant stoichiometry to differentiate geologic-derived P sites in subtropics, and three functional group plants have adopted different stoichiometric strategies under variable nutrient conditions.