Plant material

The most dominant canopy and subcanopy evergreen tree species were chosen for the study. For each species, individual trees were randomly selected from within the VCR2 plot. Branches from the same set of individual trees were sampled during both the seasons. Leaf samples were collected during two seasons: 1) the hottest and driest period of the year during October 2017, referred to as ‘end of dry’ period and 2) the end of the wet season during March–April 2018, referred to as the ‘wet’ period (Supporting Information Figure S1). Plant material was collected in both seasons from three individuals from each of five commonly occurring evergreen tree species: Hymenaea courbaril L. (Fabaceae), Brosimum rubescens Taub. (Moraceae), Amaioua guianensis Aubl. (Rubiaceae), Cheiloclinium cognatum (Miers) A.C.Sm. (Celastraceae) and Mouriri apiranga Spruce ex Triana. (Melastomataceae). Plant material from three individuals of two further species, Chaetocarpus echinocarpus (Baill.) Ducke (Peraceae) andTetragastris altissima (Aubl.) Swart (Burseraceae), was only collected in the wet period; and one tree was sampled during the end of dry period for C. echinocarpus (Supporting Information Table S1). Among the species studied, H. courbaril is the most dominant emergent tree with an average height of 29.9±0.9 m. C. echinocarpus (12.7±0.5 m), T. altissima (11.6±0.5 m), B. rubescens (10.4±0.6 m) and A. guianensis (9.5±0.3 m) are mid storey trees while C. cognatum (7.1±0.2 m) and M. apiranga(6.8±0.4 m) being the understorey trees.
Trained climbers harvested sunlit canopy branches of the trees between 07:00 to 08:00 AM. The excised branches were separated into small twigs and transported to the lab (~35km) in closed Styrofoam boxes with ice packs. Heat treatment assays were done typically within 12h of branch harvest. Fully expanded mature leaves were sampled in all cases, but during the end of the dry period campaign, H. courbaril trees had a new flush of leaves and hence, unavoidably for this species younger leaves were also sampled.