Anatomical and physiological trade-offs underlying the leaf economics spectrum in tropical Andean montane forests

The leaf economic spectrum (LES) offers a comprehensive framework that elucidates the global covariation of leaf functional traits based on an investment and return analysis in leaf tissues, and reflects resource-acquisitive and resource-conservative plant strategies. Yet, this framework has focused on whole-leaf morphological, chemical and physiological traits, offering little insight about the role of the underlying anatomy. Anatomical traits vary widely and are likely to play a pivotal role in determining whole-organ traits, and also influence community assembly and ecosystem function. Here, using leaf anatomical metrics in 63 tropical Andean plant species we aimed to understand the fundamental anatomical trade-offs underlying the LES in these mountain forests.

We measured 50 traits (41 anatomical and 9 foliar) and used Spearman correlations, principal component analysis and reduced major axis regressions to examine the physiological trade-offs between leaf anatomical characteristics and foliar traits associated with the LES.

Thicker leaf tissues and larger vascular bundles were linked to conservative strategies, whereas traits related to carbon fixation - particularly palisade mesophyll size - were associated with acquisitive strategies. In addition, mesophyll organization, including the ratio of palisade to spongy mesophyll and cell shape, influenced resource acquisition and photosynthetic rate.

Our findings show that conservative strategies predominated in these upper Andean forests; however, a clear acquisitive-conservative gradient persisted and was strongly associated with leaf anatomical traits. These findings indicate that anatomical variation represents a key functional dimension of the LES and provides new insights into its structural basis in tropical montane ecosystems.