Woody encroachment and leaf functional traits of ground-layer savanna species

Abstract

Changes in pyrodynamics, such as fire suppression, drive woody encroachment in savanna and grassland ecosystems worldwide. The filters imposed by encroachment promote floristic changes in the ground-layer community, decreasing species richness, and providing species replacement. However, functional aspects are still poorly understood, especially the role of leaf anatomical traits. Thus, our aim was to investigate the leaf trait changes in the ground-layer community of a Cerrado area in response to changes in litter and light, caused by woody encroachment. Through a field experiment, we simulated higher amounts of litter biomass and increased shading of the plant community for 2.5 years. We measured leaf tissue thickness, specific leaf area (SLA), pigment concentration and photosynthetic traits, such as carbon assimilation (A_max), stomatal conductance (g_s) and quantum efficiency of photosynthesis (α). Our results showed that shading is the main factor altering leaf functional traits, with the post-shading ground-layer community exhibiting more acquisitive resource-use strategies such as reduced leaf tissue thickness, higher SLA, and higher pigment concentration compared to plants under non-encroached conditions. However, these leaf responses were not sufficient to ensure the maintenance of higher photosynthetic performance (A_max, g_s and α) in the study species. Therefore, we demonstrate that the studied leaf functional traits of the ground-layer community are insufficient to ensure persistence and diversity in this new scenario. With the change in species composition promoted by encroachment, some shade-tolerant and generalist plants exhibit responses that contribute to their survival and occurrence.