Without water, forests lose their ability to absorb CO₂
To survive periods of drought, trees halt photosynthesis, a highly water-intensive process. For every molecule of CO₂ absorbed by a tree leaf, an average of around 400 water molecules are released. Entire forests may then end up emitting more CO₂ than they capture.
Trees rely on water for photosynthesis, a process that consumes carbon dioxide (CO₂) and releases water vapor through stomata, tiny openings on leaf surfaces. For every molecule of CO₂ absorbed, approximately 400 water molecules are released. As droughts become more common, trees may stop absorbing CO₂, turning from carbon sinks to sources.
Stomata, through which CO₂ enters, also release water, creating a cycle of transpiration. When water is scarce, trees close stomata to conserve moisture, halting transpiration and photosynthesis. This can lead to cavitation, where water turns to gas, blocking water flow and causing leaves to dehydrate. Drought-induced stomatal closure, coupled with tree death, can cause forests to emit more CO₂ than they absorb, reversing their role as carbon sinks.
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