Tropical rainforest, Queensland (photo credit: Daniel Falster)
New research reveals the amount of carbon dioxide released by trees into the atmosphere under a warming climate could be considerably less than currently predicted.
Published in the prestigious journal Science today, the new findings are from an international research team that includes Chief Scientist at Western Sydney University's Hawkesbury Institute of the Environment, Distinguished Professor Ian Wright.
The research shows the amount of CO2 respiring from tree trunks is not expected to increase as sharply as currently thought under a warming climate.
The findings give scientists important insights for predicting the amount and movement of CO2 in our ecosystems as a result of warming temperatures, and strengthen scientists' understanding of plant thermal acclimation – the way that plants respond to changes in temperature.
Professor Wright and the international research team studied trees from around the world to measure the rate of carbon dioxide they produce from their stems, known as respiration, and to test new theory for how respiration rates respond to environmental changes.
Plants and trees respire to make energy to grow, and release carbon dioxide as a by-product. The respiration from their woody stems is a major contributor to the earth's annual carbon 'flux' – or the rate at which CO2 is added or removed from the atmosphere.
Scientists have long expected that a warming climate will inevitably lead to plants increasing the amount of carbon dioxide they release into the atmosphere – in turn, leading to even more warming.
"This is likely true, but this latest research reveals that carbon fluxes under warmer future climates will not increase as much as currently thought," said Professor Wright.
Professor Wright and colleagues tested their theory using a global dataset of wood respiration consisting of thousands of measurements made on hundreds of species, from field sites spanning all major climate zones of the world.
This included data from Australian savannas, rainforests and woodlands measured by Professor Wright and his team over the last decade.
He said the findings give scientists new information about how plant CO2 production changes over a long period, depending on environmental conditions.
Mallee woodland, western New South Wales
"Short-term, temperature-driven changes in plant respiration rates are measured in seconds, minutes and hours. Due to the quick-acting enzymatic processes in plant tissues the changes in plant respiration are very fast, and predictable," explained Professor Wright.
"This contrasts with the long-term, temperature-driven changes in respiration rates that are measured in months, years and decades. Most global ecosystem models in the past have assumed that the same short-term behaviour in plants also applies over a longer time period, but this is not the case.
"We now know that thermal acclimation over long time-scales will dampen the positive feedbacks between climate warming and carbon emissions from plants."
The research was led by scientists at Tsinghua University, together with researchers drawn from around the world including Western Sydney University, Imperial College London, University of Reading, and the University of California Berkeley.
Dr Han Wang and lead author Han Zhang from Tsinghua University said it has only been recently that the researchers have had sufficient global data to test if previous models were potentially overestimating stem respiration from trees.
Professor Sandy Harrison from the University of Reading, one of the world's leading vegetation modellers, said the global discovery has significant implications for how scientists predict global carbon fluxes under future climates.
"These findings give scientists a new approach for assessing the degree to which ecosystems around the globe can slow the rate of warming," said Professor Harrison.
Professor Wright said the research has significant impact, as future climates are predicted to have more frequent and more intense events such as heatwaves, fires, droughts and floods.
"We're already seeing that play out both here in Australia and around the world. However, these new findings suggest that, to some extent, ecosystems globally will slow the trends in one key driver of these changes – elevated atmospheric CO2," he said.
Professor Wright in the field, chiselling bark off a tree to get to the wood
