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Vegetation can undergo various adaptations in response to drought, including changes in its structure and physiology. Researchers at the Max Planck Institute for Biogeochemistry in Germany, led by Dr. Wantong Li and Dr. Rene Orth, have conducted a new study that examines the different pathways of vegetation’s response to drought globally.

By utilizing state-of-the-art satellite-derived datasets and explainable machine learning methods, the researchers have discovered that vegetation’s physiology in many ecosystems deviates from its structure during drought on a global scale. This breakthrough finding, published in Nature Communications, enhances our understanding of how Earth’s ecosystems react to water scarcity.

Soil moisture drought is becoming more prevalent and severe worldwide, impacting vegetation by increasing the risk of carbon starvation and hydraulic failure, which can ultimately lead to plant death. How vegetation responds to drought, in turn, has diverse effects on climate.

Previous assessments of drought’s impact on vegetation have primarily focused on changes in plant structure. For example, satellite data has provided measurements of leaf surface area, vegetation coverage, and density. However, this new study takes a different approach by utilizing satellite-based measurements and explainable machine learning methods to isolate physiological changes from structural changes in response to drought. The researchers analyzed high-resolution satellite data collected between 2018 and 2021, which encompassed years with intense drought events, giving a comprehensive global perspective.

By examining severe droughts, the team successfully identified physiological responses related to photosynthesis, evaporation, and water content. Two plant functions were found to be most affected: the exchange rates of CO2 and water vapor regulated by stomata, and the efficiency of solar radiation utilization for photosynthesis or absorption by leaves.

The advantage of this new approach is manifold. Firstly, it provides a more complete understanding of vegetation’s response to drought by incorporating the global effects on the biological functioning of plants, rather than solely considering their structural appearance. The previous approach might have underestimated the timing, severity, and scale of vegetation affected by drought. Secondly, vegetation’s physiology typically responds faster to stress than its structural appearance, allowing for earlier recognition of drought impacts. For instance, while a brownish meadow may visibly indicate drought stress, other plants, especially trees, can appear normal while already experiencing significant drought-induced physiological changes.

The study also revealed that vegetation in semi-arid and arid regions showed the most pronounced effects, indicating a strong correlation between background climate and physiological responses. In wetter regions, vegetation may still appear green or even greener during drought events, but their functioning is reduced, highlighting a clear disparity between functional and structural changes observed during severe drought.

Dr. René Orth, co-author and head of the research group at MPI-BGC, emphasizes the importance of understanding vegetation’s response to drought for predicting and mitigating the effects of climate change. These findings provide a more accurate foundation for comprehending the biological and environmental feedback mechanisms of ecosystems, which play a crucial role in shaping the future of our planet.

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