The study, led by researchers from the South China Botanical Garden of the Chinese Academy of Sciences, is based on 40 throughfall reduction experiments carried out in forests around the world. Together, the experiments represent one of the most extensive field-based investigations of drought acclimation—the ability of an organism to adjust its functional traits in response to persistent environmental change. The findings, published in the Proceedings of the National Academy of Sciences on Aug. 24, challenge a widely held assumption that mature trees can gradually adapt to a drier climate by making their water-conducting tissues safer or by modifying their photosynthetic machinery.

The experiments were designed to reproduce drought while preserving the ecological complexity of a real forest. Researchers installed gutters and other collection systems beneath forest canopies to intercept a portion of rainfall before it reached the ground. This reduced the amount of water entering the soil, while trees remained rooted in natural soils and continued growing alongside neighboring plants, fungi, microbes, and other members of their forest communities. The approach avoided a major limitation of many earlier studies, which examined potted seedlings or compared forests located along natural rainfall gradients. Those methods can reveal important biological responses, but they may not fully represent how established trees behave under long-term drought in their natural surroundings.

Across the 40 experiments, researchers examined 24 physiological traits associated with water transport, drought resistance, and carbon acquisition. These included characteristics related to xylem function, the specialized vascular tissue that carries water from roots to leaves; embolism resistance, which describes a tree’s ability to prevent air bubbles from blocking that transport system; hydraulic efficiency; leaf nutrient concentrations; and photosynthetic capacity. Across forests experiencing different climates and levels of water stress, most of these traits changed little. The trees did not substantially increase their resistance to embolism, improve their hydraulic efficiency, or alter their leaf nutrient composition and photosynthetic machinery in ways that would indicate strong physiological acclimation.

That apparent stability may initially sound encouraging, but the study revealed a potentially serious cost. As drought intensified, the water potential of tree tissues declined. Water potential is a measure of the energy status of water inside a plant, and increasingly negative values indicate that the tree is under greater tension as it pulls water from drying soil toward its leaves. At the same time, the trees’ embolism resistance remained largely unchanged. This combination narrowed what scientists call the hydraulic safety margin—the difference between the water conditions a tree normally experiences and the threshold at which its xylem becomes vulnerable to catastrophic water-transport failure.

Hydraulic safety margins function much like a buffer. When the margin is wide, a tree can tolerate a substantial decline in tissue water potential before air enters its xylem and disrupts the continuous water columns needed to supply leaves. When the margin narrows, comparatively small additional changes in soil or atmospheric dryness can push the tree toward hydraulic dysfunction. Once embolism spreads through enough of the xylem, leaves may be starved of water, photosynthesis can collapse, and entire branches or trees may die. The global experiments indicate that trees under prolonged drought were increasingly close to this threshold without making a corresponding physiological adjustment to move the threshold farther away.

The study also identified a striking separation between carbon uptake and carbon storage. Net photosynthesis declined under drought, largely because stomata—the microscopic pores on leaf surfaces that regulate gas exchange—closed to limit water loss. Stomatal closure helps prevent dehydration, but it also restricts the entry of carbon dioxide, reducing the raw material available for photosynthesis. Despite this decline in carbon assimilation, the researchers found that nonstructural carbohydrates, including soluble sugars and starch, remained relatively stable. These compounds serve as internal reserves that can support maintenance, growth, defense, and recovery when conditions improve.

The stability of stored carbohydrates suggests that reduced photosynthesis did not necessarily translate into immediate carbon starvation during the drought periods represented in the experiments. Trees may have drawn on existing reserves, reduced growth, or adjusted the allocation of carbon among different tissues while preserving their internal stores. This finding complicates a common explanation for drought-related tree decline, in which mortality is expected to result primarily from the gradual exhaustion of carbohydrates. The results instead point to hydraulic failure as a potentially more immediate danger, especially when drought causes water transport to approach its physical limits before stored carbon is substantially depleted.

The researchers propose that maintaining existing hydraulic and photosynthetic capacities could still provide an advantage during brief periods of improved water availability. After rainfall, a tree that has not significantly reduced its photosynthetic machinery may be able to resume carbon assimilation rapidly and take advantage of favorable conditions. However, that strategy may carry increasing risks as drought becomes more intense or persistent. A tree can remain capable of rapid carbon gain after rainfall while simultaneously operating with a dangerously narrow hydraulic safety margin. In other words, physiological capacity does not automatically equal physiological safety. The ability to continue functioning under favorable conditions may coexist with a limited ability to withstand further drying.

The findings have broad implications for ecological models and projections of future forests. Many models assume that plants will acclimate to climate change by altering traits such as hydraulic resistance, photosynthetic capacity, leaf chemistry, or drought tolerance. If trees in natural forests generally make only limited adjustments to these traits during prolonged drought, models that assume substantial acclimation could overestimate forest resilience. As droughts become more frequent and severe, the decisive factor may not be whether trees can preserve their carbon reserves, but whether their water-transport systems can continue operating as soil moisture falls and atmospheric demand for water rises. The study’s central warning is therefore clear: forests may retain the machinery needed to recover after rainfall while moving ever closer to irreversible hydraulic damage. Recognizing that narrow margin will be essential for predicting forest mortality, improving climate forecasts, and protecting ecosystems that support biodiversity and human societies.

Subject of Research: The physiological acclimation of forest trees to prolonged drought, with emphasis on hydraulic safety, water transport, photosynthesis, and carbon storage.

Article Title: Declining hydraulic safety in a drier world

News Publication Date: 24-Aug-2026

Web References: https://doi.org/10.1073/pnas.2622754123

References: Proceedings of the National Academy of Sciences; DOI: 10.1073/pnas.2622754123

Image Credits: Image by CHEN Zhicheng

Keywords: forests, drought, climate change, tree physiology, hydraulic safety margin, embolism resistance, xylem, photosynthesis, nonstructural carbohydrates, forest ecosystems, drought acclimation, water stress, plant hydraulics

The Scots pine is notable for its adaptability to harsh conditions and its widespread distribution across Europe and parts of Asia. This species plays a critical role in forest ecosystems, providing habitat for various wildlife and contributing to soil health. However, with the rise in air pollution, especially in urbanized and industrial regions, there are legitimate concerns about how these pollutants might affect the competitive relationships between Scots pine and neighboring plant species. The study undertaken by Simin and their colleagues seeks to investigate whether these pollutants hinder the positive interactions among plant communities or disrupt their overall health.

The methodology employed in this research is quite comprehensive. The scientists established experimental plots containing Scots pine trees alongside other native plant species. By exposing these plots to varying levels of air pollutants, the researchers could meticulously assess how these conditions impacted not just the Scots pine, but also the broader plant community interactions. The design of the experiment allowed for a controlled examination of factors such as nutrient exchange, root interactions, and even allelopathic effects — where one plant species produces biochemicals that influence growth, survival, and reproduction in other species.

One of the pivotal findings of the research was that, contrary to earlier hypotheses, air pollutants did not significantly impair the beneficial interactions between Scots pine and its neighboring plant species. The study indicated that these trees retained their ability to engage in important ecological functions such as nutrient cycling, which is vital for sustaining forest health. This revelation sheds light on the resilience of Scots pine as a species, suggesting that they possess mechanisms to thrive despite the presence of harmful pollutants in their environment.

Air pollutants, particularly sulfur dioxide and nitrogen oxides, are known to have detrimental effects on plant life. However, the research proposed that Scots pine’s physiological adaptations may play a role in mitigating these negative impacts. The tree’s thick bark and deep root system could provide it with certain levels of protection against pollutants, allowing it to continue supporting surrounding plant communities. This resilience may offer insights into how forest ecosystems can be managed under the pressures of pollution.

Achieving a deeper understanding of these interactions is vital not only for the health of forest ecosystems but also for global efforts to combat climate change. Forests act as significant carbon sinks, and their efficiency in sequestering carbon can be influenced by the health of plant interactions. If pollutants disrupt these natural processes, there could be long-term ramifications for carbon storage and overall climate stability.

In addition to its ecological implications, this research may offer valuable applications in forestry practices. As we strive for sustainable management of forest resources, knowing that Scots pine can sustain interspecies interactions despite the presence of air pollutants can inform reforestation and conservation efforts in degraded landscapes. It may encourage the planting of Scots pine in areas previously considered unsuitable due to pollution risks.

Moreover, the findings signal a need for continued research into the effects of air quality on flora and their interactions. As urban areas expand and industrial activities increase, understanding plant resilience becomes ever more critical. Researchers are poised to delve deeper into the molecular mechanisms underpinning these interactions, offering the potential for innovative strategies that promote healthier ecosystems in polluted environments.

Another potential avenue for future research could involve examining how different levels and types of air pollutants interact with various plant species beyond Scots pine. By broadening the scope of study to include diverse flora, scientists could map out a clearer picture of forest dynamics in polluted environments, contributing significantly to the fields of botany and ecology.

The research on Scots pine and air pollutants is not merely academic; it resonates with pressing environmental concerns that will shape policy decisions in the coming years. As we confront a future of climate uncertainty, it is crucial that our strategies are grounded in scientific evidence. The resilience of Scots pine highlights an important narrative of adaptation and ecological harmony that may inspire conservation initiatives worldwide.

In summary, the study sheds light on the surprising robustness of Scots pine against air pollutants, suggesting that while pollution poses serious threats to plant health, some species possess the resilience necessary to maintain vital interspecies relationships. This research opens up new pathways for sustainable forestry and conservation practices, ensuring that forests continue to thrive even in compromised environments. It serves as a testament to the incredible adaptability of nature and the importance of understanding ecological interactions in the face of environmental challenges.

With the knowledge gained from this study, the commitment to fostering resilient ecosystems has never been more critical. As we move forward, embracing the resilience of species like Scots pine may not only guide reforestation efforts but also inspire broader strategies aimed at protecting our planet for future generations.

Subject of Research: Interactions Between Scots Pine and Air Pollutants

Article Title: Between-plant interactions in Scots pine are not impaired by air pollutants

Article References:

Simin, T., Ryalls, J.M.W., Welling, O.E.I. et al. Between-plant interactions in Scots pine are not impaired by air pollutants. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-025-03175-3

Image Credits: AI Generated

DOI:

Keywords: Scots pine, air pollution, plant interactions, ecological resilience, forest management, environmental science.