[ad_1]
When it comes to climate change and the Amazon rainforest, the news is never good. In 2019 and 2020, the news was dominated by images of burning forests and land ravaged by climate change and illegal logging.
But there are still many scientists who do not yet know the mysterious Amazon.
A new study published Friday in Scientific advances is a good example. In the study, scientists reveal puzzling ecological traits in the wetter parts of the Amazon, suggesting that the rainforest may be harder than we think.
Neural networks – In the study, scientists are examining the relationship between increased air dryness (also known as vapor pressure deficit) and gross primary production in the Amazon.
Gross primary production refers to the total amount of carbon that forest plants “fix” or take up during photosynthesis.
The scientists used observational data from a nine-year period between June 2007 and May 2016, inputting it into a machine learning tool called an artificial neural network. These networks helped the researchers analyze and compare their findings with existing models and simulations of how dry air alters the Amazon’s ability to act as a carbon sink.
“What I wanted to do was basically take different environmental predictors and input them into a model so that I could predict changes in photosynthesis,” Julia K. Green, lead author of the study and researcher at the Science Laboratory of the Climate and the Environment in France, says Reverse.
Simulation versus reality – Armed with their model, Green and his colleagues then compared the typical predictions of land surface simulations to what is actually happening in the Amazon.
“These are the models we use to make climate change predictions. And so our predictions may not be as good or as accurate as these models,” says Green.
The wetter parts of the Amazon boast trees with deep root systems. But models show that vegetation in these areas can become stressed due to “water deficit,” caused by increasingly drier air or soil, Green says. This water deficit can have a significant impact on photosynthesis.
“Plants have these little pores on their leaves called stomata. And what ends up happening is that in order to absorb carbon dioxide, the plant has to open the stomata of their leaves to allow the gas to be absorbed, ”says Green.
But because “the plant absorbs carbon dioxide, it loses water through the surface of the leaves because the air is drier,” says Green. Result: “the drier the air, the more the stomata will become closed” to conserve water, she explains.
The researchers speculated – and their models too – that closing the stomata from the air drought would reduce photosynthesis.
“What we were seeing is that in model simulations with just a little bit of drought, photosynthesis in those areas of rainforest was really decreasing in the models. And we weren’t sure if that necessarily sounded realistic, ”says Green.
This is where artificial neural networks came in – Green used their results to come to a startling conclusion: The simulation models were wrong.
“What we ended up seeing was that as the vapor pressure deficit increases, this photosynthesis in these really very humid areas of the forest. [increases],” she explains.
The reason has to do with the nature of the Amazon rainforest itself. The Amazon has a very “dynamic” forest cover, says Green, which compensates for stomata closure, counterintuitively increasing photosynthesis.
“Once the air starts to dry, what ends up happening is the forest ends up shedding a lot of those old leaves at the top of the canopy,” says Green. “New, younger leaves eventually replace them. And these new, younger leaves have a much higher photosynthetic capacity than the leaves they replace.”
Natural resilience – The Amazon serves one of the world’s most important carbon sinks. And that carbon sink relies on photosynthesis to survive.
But these results suggest that the Amazon has its own natural resilience during periods of drier air. But whether the results suggest the Amazon is more resistant to extreme weather events, such as drought brought on by climate change, is unclear, Green says.
“This study, although it shows that forests are more air drought tolerant than we thought and what is described, does not say that the air should dry to levels we do not have. seen so far so that everything goes well ”. Green said.
Abstract: Earth system models predict that increased atmospheric and soil drought will reduce photosynthesis in the Amazon rainforest, with big implications for the global carbon cycle. Using in situ observations, sun-induced fluorescence, and non-linear machine learning techniques, we show that in reality this is not necessarily the case: in many wetter parts of this region, photosynthesis and biomass tend to increase with increased atmospheric dryness. , despite the associated reductions in the conductance of the canopy in CO2. These results can be largely explained by changes in the properties of the canopy, in particular, the new leaves rinsed during the dry season have a higher photosynthetic capacity than the leaves they replace, compensating for the negative stomatal response to increased drought. . As atmospheric drought increases with climate change, our study underscores the importance of reframing how we represent the photosynthetic response of ecosystems to atmospheric drought in high humidity regions, to accurately quantify the terrestrial carbon sink.
[ad_2]
Source link