Photosynthetic quantum efficiency in <scp>south‐eastern</scp> Amazonian trees may be already affected by climate change
Rakesh Tiwari, Emanuel Gloor, Wesley Jonatar Alves da Cruz, Beatriz Schwantes Marimon, Ben Hur Marimon, Simone Matias Reis, Igor Araújo, H. Krause, Martijn Slot, Klaus Winter, David J. B. Ashley, Raiane G. Beú, Camila Mourão Borges, Maura Da Cunha, Sophie Fauset, Laura dos Santos Ferreira, Maélly Dállet Alves Gonçalves, Thaynara T. Lopes, Eduardo Q. Marques, Natalia G. Mendonça, Natana G. Mendonça, Pedro T. Noleto, Carla Heloísa Luz de Oliveira, Milene A. Oliveira, Saulo Pireda, Nayane Cristina Candida dos Santos Prestes, Denilson M. Santos, Eduarda Bernardes Santos, Ediméia Laura Souza da Silva, Izabel A. de Souza, Luciana Januário de Souza, Ângela Pierre Vitória, Christine H. Foyer, David Galbraith
Abstract
Abstract Tropical forests are experiencing unprecedented high‐temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high‐temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield ( F v / F m ) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T 50 was calculated as the temperature at which F v / F m was half the maximum value. T 5 is defined as the breakpoint temperature, at which F v / F m decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T 50 and T 5 varied between species, with one mid‐storey species, Amaioua guianensis , exhibiting particularly high T 50 and T 5 values. While the T 50 values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T 5 values of several species are now exceeded under present‐day maximum air temperatures.