Photosynthetic quantum efficiency in South-Eastern Amazonian trees may
be already affected by climate change
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 (Fv/Fm)
of photosystem II was measured in seven dominant tree species using leaf
discs exposed to varying levels of heat stress.
T50 was calculated as the temperature at which
Fv/Fm) was half the
maximum value. T5 is defined as the breakpoint
temperature, at which
Fv/Fm) decline was
initiated. Leaf thermotolerance in the rapidly warming Southern Amazonia
was the highest recorded for forest tree species globally.
T50 and T5 varied between
species, with one mid storey species, Amaioua guianensis, exhibiting
particularly high T50 and
T5 values. While the T50
values of the species sampled were several degrees above the maximum air
temperatures experienced in southern Amazonia, the
T5 values of several species are now exceeded
under present-day maximum air temperatures.