This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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.
Many previous attempts to answer this question have relied on evidence from potted plants or natural rainfall gradients, leaving uncertainty over whether trees growing in natural forest environments respond in the same way. Now, a new global forest study that better reflects natural conditions has found that trees do not substantially alter their physiological traits to cope with prolonged drought. The study, led by researchers from the South China Botanical Garden (SCBG) of the Chinese Academy of Sciences (CAS), is based on 40 throughfall reduction experiments conducted across forests worldwide and represents one of the most comprehensive field-based assessments of drought acclimation to date.
It was published in Proceedings of the National Academy of Sciences. In the experiments, gutters installed beneath the forest canopy diverted part of the incoming rainfall before it reached the soil, reducing water availability while trees remained rooted in natural soils and surrounded by their forest communities. This approach allowed researchers to examine long-term drought responses under realistic forest conditions, rather than in artificial pot experiments or across natural rainfall gradients.
The researchers examined 24 physiological traits related to water transport, drought resistance and carbon gain. Across forests spanning contrasting climates and drought conditions, traits including embolism resistance, hydraulic efficiency, leaf nutrient concentrations and photosynthetic capacity showed little change. "Trees showed remarkably little adjustment in their hydraulic and photosynthetic capacities despite prolonged reductions in water availability," said Liang Xingyun from SCBG, the study's first author.
"By maintaining these capacities, trees may be able to maximize carbon assimilation during favorable periods following rainfall, when water becomes available and conditions for photosynthesis improve." However, this stability was associated with an important consequence. Drought caused tree tissue water potentials to decline, while embolism resistance remained largely unchanged. As a result, hydraulic safety margins—the buffer between the water status a tree experiences and the point at which its water-transport system becomes vulnerable to damage—became significantly narrower.
Trees were therefore operating closer to their hydraulic limits without substantially increasing their resistance to hydraulic damage. The researchers also revealed a contrasting pattern in carbon uptake and storage. Net photosynthesis declined under drought, largely because stomata closed to conserve water.
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