Studying the invisible in terrestrial ecosystems to save our planet

Our climate is warming rapidly and rising temperatures are impacting the physical environments that support entire ecosystems. Humans and animal species are facing daunting challenges to their survival due to climate change. The perspective is not lost on NUS climate change ecologist, Assistant Professor Luo Xiangzhong. For him, childhood admirations for the work of early natural philosophers such as German naturalist Alexander von Humboldt, coupled with a desire to tackle the problem of climate change, introduced him to the world of science. climate change ecology.

A doctoral trip to a Foucault covariance tower in a Canadian forest sealed the deal. There, looking at the colorful canopies of autumn, he realized that the tower was monitoring something invisible – the amount of water and carbon dioxide the forest was using and absorbing. Knowing that the uptake of carbon dioxide by the forest had increased for 10 years for reasons still unknown crystallized his interest in the links between the visible and the invisible, and how climate can impact on ecosystems in ways that we cannot directly see.

A recent study he conducted clearly illustrates this relationship. The study found that the amount of carbon dioxide absorbed by terrestrial ecosystems, such as forests, may be linked to the availability of water, which becomes scarce during droughts. This highlighted the significant impact of droughts on the ability of forests to absorb carbon dioxide (or CO2) – the main greenhouse gas causing climate change – from the atmosphere.

We recently caught up with the Faculty of Arts and Social Sciences geographer to learn more about the importance of climate change ecology, its sister questions of the carbon cycle and global photosynthesis, and his research.

What is the ecology of climate change?

Assistant Professor Luo: Climate change ecology studies the interactions between climate change and natural ecosystems. It is a two-way process. On the one hand, climate change is influencing ecosystems, leading to questions about whether rising temperatures and reduced rainfall can cause rainforests to collapse. On the other hand, ecosystems can impact climate by modulating the carbon and water cycles on Earth. For example, ecosystems can mitigate global warming by absorbing CO2 of the atmosphere through photosynthesis. Many environmental interactions and feedbacks morph into a rather complex relationship between terrestrial ecosystems and climate change.

When we talk about ecosystems, we often think of trees and leaves. However, advances in Earth observation techniques over the past 20 years, such as eddy covariance, leaf gas exchange, and Earth system modeling, have helped us see far beyond that. It also represents a great opportunity for us to push the boundaries of knowledge and better understand the dynamics of ecosystems.

Could you share more details about your recent study on the link between droughts and the ability of forests to absorb carbon dioxide?

Assistant Professor Luo: Ecosystems absorb different amounts of CO2 of the atmosphere each year, resulting in variations in atmospheric CO2 concentration (for example, when terrestrial ecosystems absorb more CO2CO2 the level of concentration in the atmosphere increases more slowly). Scientists discussed the reason for ecosystem CO variations2 absorption and atmospheric CO2 level of concentration, and provided rather contrasting explanations – some suggest temperature anomalies are the main reason, some suggest soil moisture, others point to historical land use changes.

In this study, we examined the change in magnitude of variation over the past 60 years and found a dominant role played by tropical extreme droughts in modulating atmospheric CO2 variation. This new discovery advances our understanding of the global carbon cycle, and sheds light on how tropical droughts, previously neglected and poorly accounted for in climate and carbon models, have in fact modulated the long-term variation of atmospheric CO2. When extreme droughts occur, ecosystems experience downregulation of photosynthesis, as well as tree mortality, fires, regeneration and decay of dead wood. These processes would make the ecosystem CO2 absorption more variable in the long term. In particular, we found that droughts in tropical Asian ecosystems have outsized impacts on the long-term variation of the global carbon cycle, which will motivate our future studies to examine the impacts of drought on ecosystems in Asia. Tropical Asia, including those from Singapore.

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