Variation in plant carbon, nitrogen and phosphorus contents across the drylands of China

Determining large-scale patterns of plant elemental concentrations and
stoichiometry along environmental gradients is critical for understanding
plant adaptive strategies and predicting ecosystem biogeochemistry
processes. However, it remains unclear as to how plant carbon (C),
nitrogen (N), and phosphorus (P) concentrations and their stoichiometry in
different organs (leaves, stems, and roots) respond to large-scale
environmental gradients in drylands. We determined C, N, and P
concentrations and their ratios in leaves, stems, and roots of plants
growing in the dryland ecosystems of China. Using threshold indicator taxa
analyses, we identified indicator species of plant C, N, and P responses
to aridity and soil properties. The arithmetic averaged concentrations of
C, N, and P in drylands were 414, 18.7, and 1.38 mg/g for leaves,
respectively; 445, 12.1, and 1.08 mg/g for stems, respectively; and 418,
10.5, and 0.89 mg/g for roots, respectively. The C : N, C : P, and N : P
ratios were 25.2, 386, and 16.3 for leaves, respectively; 42.8, 592, and
14.8 for stems, respectively; and 46.8, 658, and 15.6 for roots,
respectively. Aridity and soil pH generally exerted positive effects on
plant N and negative effects on C and P concentrations and, thus, were
related negatively to C : N ratios and positively to C : P and N : P
ratios. The C, N, and P concentrations in organs generally increased with
increasing corresponding soil C, N, and P concentrations. Shrubs were
mainly positive indicators of plant C, N, and P concentrations in response
to aridity and soil pH, and negative indicators of soil nutrients. In
contrast, herbaceous species were mainly positive indicators of soil
nutrients and negative indicators of aridity and soil pH. These findings
indicate that plants tend to accumulate N rather than C and P with
increasing aridity and soil pH. The identification of indicator species
for plant elements in response to aridity and soil traits informs our
understanding of species-specific biogeographic patterns of organ elements
and potential adaptive strategies of plants in drylands.