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.