Forty forest drought experiments reveal trees show little physiological acclimation
Forests support much of the world's biodiversity and play a vital role in regulating Earth's climate, but they are increasingly exposed to drought. To understand the potential consequences of drought, a key question is whether trees can acclimate to prolonged water stress by altering their physiology.
A recent global study involving 40 forest experiments has found that trees show minimal physiological changes when exposed to prolonged drought conditions. Led by researchers from the South China Botanical Garden, the research challenges the assumption that forests will significantly adapt to a drier climate. Conducted across various forests worldwide, the experiments involved diverting rainfall to reduce water availability while trees remained in natural soils and surrounding forest communities.
Across the 40 experiments, traits related to water transport, drought resistance, and carbon gain showed little change. Trees maintained their hydraulic and photosynthetic capacities despite reduced water availability, suggesting they may continue to maximize carbon assimilation during periods of favorable conditions. However, this stability came at the cost of reduced hydraulic safety margins.
As trees became closer to their hydraulic limits, their ability to cope with further drought stress became compromised. The study also revealed that while net photosynthesis decreased due to stomatal closure to conserve water, nonstructural carbohydrate stores remained stable. Therefore, reduced carbon uptake did not lead to clear depletion of stored carbon during the experimental droughts.
The findings suggest that carbon depletion may not be the primary limitation for trees exposed to prolonged drought, but rather the narrowing of hydraulic safety margins. The authors emphasize that maintaining physiological capacity does not guarantee trees' safety during drought. They highlight hydraulic safety margins as a critical concern for forests facing increased drought frequency and severity.
By recognizing trees' limited capacity for acclimation, researchers can better understand and potentially protect forests in the face of ongoing climate change.
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