Are leaf anatomical traits strong predictors of litter decomposability? Evidence from upper Andean tropical species along a forest successional gradient.

Litter decomposability has been linked to "soft" traits of green leaves, but relationships with "hard" traits associated with leaf anatomy remain unexplored. Examining anatomical traits within the leaf economic spectrum may enhance our understanding of litter decomposability. In this study, we analyzed the relationships between leaf anatomical traits and decomposability at both species and community levels along a successional gradient of upper Andean tropical forests in Colombia. We conducted a reciprocal translocation field experiment with 15 upper Andean species in 14 permanent plots around Bogotá, collecting 2520 litterbags at four times (3, 6, 12, 18 months). Using a multiple regression model based on foliar traits, we estimated decomposability for the remaining 48 species that compose the plant community (63 species in total) in the studied successional gradient. We measured several leaf anatomical traits in all 63 species and calculated community-weighted means and functional diversity indices with the most effective anatomical predictors of decomposability. We found that thicker cuticles, larger vascular bundles, higher spongy mesophyll proportion, and lower palisade mesophyll proportion are related to low decomposability. Plant communities with thicker protective structures slow down decay rates, while large palisade tissues with cylindrical cells increase litter breakdown. Decomposability did not change along succession due to the balance between high functional evenness in secondary forests and high functional richness in mature forests. Despite potential circularity and interdependence between functional diversity metrics, our study provides novel insights into the anatomical basis of decomposability and community dynamics in successional gradients of upper Andean tropical forests.