Variation in leaf litter silicon concentration along soil fertility and climate gradients in tropical montane forests in western Panama

Background and aims: Leaf silicon (Si) accumulation may mitigate diverse biotic and abiotic stresses, including nutrient deficiencies. In tropical montane forests, we therefore predicted that leaf litter Si will be negatively correlated with soil fertility, and that leaf litter Si and soil water soluble Si will decrease in colder and wetter environments due to reduced uptake of Si through transpiration and Si leaching from soil. Methods: We examined leaf litter Si and soil water extractable Si from topsoil and subsoil along soil fertility and climate gradients in two tropical montane forest area, Fortuna (multiple parent materials) and Baru (uniform volcanic deposits) in western Panama. To consider the effects of species turnover on leaf litter Si along the gradients, we measured leaf Si in 136 tree species in this region. Results: Leaf litter Si was uncorrelated with soil fertility across Fortuna and Baru. As predicted, leaf litter Si and water extractable Si from subsoil increased with temperature and decreased with precipitation only in Baru. High leaf Si accumulation occurred in some families such as Burseraceae, Magnoliaceae and Ulmaceae. Leaf litter Si was correlated with community-weighted mean leaf Si and water extractable Si from subsoil, suggesting synergistic effects of species turnover and subsoil Si availability on leaf litter Si. Conclusion: Our study suggests that leaf litter Si concentration is not linked with soil fertility. However, variation in leaf litter Si could be driven by climate factors and possibly mediated by species turnover and subsoil Si availability in tropical montane forests.