Bedrock geology interacts with altitude in affecting leaf growth and foliar nutrient status of mountain vascular plants

Aims Altitude is often used as a proxy for ascertaining how warming affects plant growth and leaf level properties. However, we have a poor understanding of how the effects of altitude-related warming varies across geology. Therefore, this study examined the independent and interactive effects of altitude and geology and species on plant growth and foliar nutrient status. Methods We determined leaf growth rates and concentrations of major nutrients (nitrogen, N and phosphorus, P) in leaves of five species across two altitudinal gradients (1200-2200 m) in the Dolomites (south-eastern Alps, Italy). The two transects were located on carbonate bedrock and silicate bedrock, respectively. We also determined concentrations of inorganic and organic N and P forms in soils, and d N-15 signature in leaves and soils. Important Findings Foliar N concentrations were unrelated to bedrock geology. The negative foliar d N-15 signature suggested that organic N was the primary source of N supply across the gradients. Foliar P concentrations were strongly affected by bedrock geology and their altitudinal patterns depended on the concentrations of organic and inorganic P forms in the soil. Phosphates and organic P appeared to be the main sources of P supply. Leaf growth rates increased with higher altitude on silicate bedrock and decreased with higher altitude on carbonate bedrock and presented a significant positive correlation with foliar N: P. In conclusion, bedrock geology interacted with altitude in controlling the foliar nutrient status mainly owing to availability of soil P and its effect on foliar nutrient stoichiometry.