Patterns and drivers of plant C:N:P stoichiometry across a 3000 km aridity gradient

Leaf element stoichiometry is crucial for understanding nutrient dynamics and carbon (C) cycling in terrestrial ecosystems. However, the biogeographical patterns of leaf C, nitrogen (N), and phosphorus (P) content and their stoichiometric relationships along aridity gradients remain poorly understood, particularly regarding their driving factors. This study examined leaf C:N stoichiometry across a 3000 km aridity gradient in China, encompassing 36 sampling sites representing forest, grassland, and desert ecosystems. We further investigated the relationships between leaf biochemical traits and environmental drivers. Results revealed that the mean leaf contents of C, N, and P at 588.29 ± 6.9, 19.11 ± 0.3, and 1.33 ± 0.03 g kg −1 , respectively. The C:N, C:P, and N:P ratios were obtained as 32.43 ± 0.64, 480.65 ± 11.36, and 15.71 ± 0.4, respectively. The leaf C:N:P stoichiometry exhibited a pervasive nonlinear pattern, and a threshold of approximately 0.7 on an aridity index (AI). Below this threshold (AI <0.7), the leaf C:P and N:P ratios decreased as AI increased, and N limitation became more evident. Conversely, these ratios increased above this threshold (AI >0.7), indicating that P availability increasingly constrained plant growth. Furthermore, plants in arid regions (AI <0.7) demonstrated strong stoichiometric homeostasis, suggesting effective physiological adaptation to environmental fluctuations. This homeostatic capacity substantially weakened in humid regions (AI >0.7), where plants showed greater stoichiometric plasticity. These findings advance our understanding of spatial patterns in leaf nutrient stoichiometry and provide critical insights for modeling ecosystem nutrient cycling under global climate change scenarios. • Leaf C:N:P stoichiometry exhibits a nonlinear pattern with a critical aridity index (AI) threshold of 0.7. • Below the threshold, leaf C:P and N:P ratios decrease, while above this threshold, these ratios increase. • In humid regions, plant growth is constrained by phosphorus limitation, while nitrogen limitation is evident near the threshold. • Plants in arid regions maintain strict homeostasis, adapting to environmental fluctuations, but this regulation diminishes in humid regions.