Contrasting effects of light, soil chemistry and phylogeny on leaf nutrient concentrations in cave-dwelling plants

Abstract

The drivers of variations in leaf nutrient concentrations in cave-dwelling plants remain poorly understood. We aimed to explore the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations in cave-dwelling plants. We quantified light availability and sampled top-soils and leaves of the co-existing herbs and ferns in three caves. We used the traditional and phylogenetic comparative methods to determine the effects of light, soil chemistry and phylogeny on leaf nutrient concentrations and the cross-species correlations between leaf nutrients. Leaf nutrient concentrations differed little among caves due to the non-significant relationships of leaf nutrient concentrations with light availability and soil nutrient concentrations across caves. The phylogenetic signals in leaf nutrient concentrations were significant for Ca, Mg and N but non-significant for the remaining nutrients. The evolutionary rates of leaf nutrient concentrations tended to increase with decreasing phylogenetic signals and were faster in herbs than ferns. These contrasting degrees of phylogenetic conservatism in leaf nutrient concentrations were best generated by Ornstein-Uhlenbeck models, i.e., stabilizing selection towards an optimum across species for P, K, S, Fe, Mn and Zn or higher optimal concentrations in herbs than ferns for Ca, Mg and N. Strong cross-species correlations between leaf nutrient concentrations such as Ca vs Mg and N vs P were found. Leaf nutrient concentrations in cave-dwelling plants showed convergent adaptations to cave environments and presented contrasting degrees of phylogenetic conservatism to produce leaf nutritional diversity for the co-existing herbs and ferns in caves.