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 δ 15N signature in leaves and soils. Important Findings: Foliar N concentrations were unrelated to bedrock geology. The negative foliar δ 15N 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 Pand its effect on foliar nutrient stoichiomctry.