Data from: Testing the biogeochemical niche hypothesis using leaves, stems and roots of 62 Artemisia species across China

The biogeochemical niche (BN) hypothesis is based on the concentrations of
the predominant elements of a given organism to be stoichiometrically
matched in order for it to function adequately. However, it is unknown how
BN is represented by different plant organs and to what extent environment
or evolution affects BN. We measured C, N, P, K, Ca and Mg concentrations
in leaves, stems and roots of 1,022 individuals of 62 Artemisia species
collected across China to quantify BNs of the three organs. The BN of
leaves was offset from and smaller in volume than that of stems and roots.
BNs of the three organs differed in their sensitivities to environmental
gradients, and leaves were less responsive to environmental variation than
stems and roots in both BN volumes and positions. Environmental gradients
had larger effects on BN positions than on BN volumes of all three organs.
The BN volumes and positions of leaves and roots had no phylogenetic
signal, while stem BN had a weak signal, i.e. repeated species divergences
from various Artemisia branches explained most of the BN variation of the
three organs. Synthesis. The BN hypothesis cannot be fully tested using
the elemental composition of a single organ owing to different
physiological mechanisms and diverse responses of BN among organs. At
least in Artemisia, leaves are strongly constrained in a limited elemental
niche space to support a relatively stable supply of elements for leaf
functioning, especially photosynthesis. In contrast, stems and roots
develop larger elemental hypervolumes also representing nutrient storage
and other functions. The BNs of Artemisia showed different environmental
responses between volumes and positions, allowing these species to adjust
elemental concentrations while maintaining the variation in overall
elemental composition under different environmental conditions. In
conclusion, BNs of extant Artemisia populations are determined mostly by
short-term phenotypic responses to current environmental conditions and/or
genotypic variation, while the recently evolved species diversity results
mostly from species-specific and organ-specific use of nutrients and
little by early divergence in the phylogeny.