Millennial Torreya Trees Are Quietly Starving for Potassium

Some of the oldest cultivated trees on Earth are quietly running out of a nutrient that ecologists rarely worry about. In the misty hills of Zhejiang Province, groves of Chinese nutmeg trees have been tended by farmers for up to sixteen centuries, producing prized edible nuts. Now a new study finds that these ancient torreya trees face a progressive and potentially severe depletion of potassium in their soils, and the shortage is quietly unraveling the nutrient recycling that has sustained these torreya trees for generations.

The findings, published in the journal Plant and Soil in 2026, come from a team led by Mengyuan Chang and Zongxing Wang of Zhejiang A and F University, as reported by ScienMag in early October 2026. The researchers took advantage of an extraordinary natural experiment: a chronosequence of Torreya grandis stands ranging from about a century old to sixteen centuries old. Because the trees in each age group grow under broadly similar climate and management traditions, differences among the groups can be attributed largely to age itself. The team sampled the full leaf, litter, and soil continuum, measuring carbon, nitrogen, phosphorus, and potassium in green leaves, fallen litter, and soil at two depths, then calculated how efficiently the torreya trees pulled nutrients back from dying leaves before dropping them.

What a Thousand Years Did to Torreya Trees

The soil results told a story of slow but relentless change. Organic carbon and total nitrogen in the soil actually increased as stands aged, a pattern consistent with centuries of litter accumulation and organic matter buildup. Total phosphorus stayed roughly stable across all age groups in both soil layers tested. Potassium broke the pattern dramatically: soil total potassium declined consistently with tree age, signaling what the authors describe as progressive potassium depletion. In other words, the nutrient plants need in large quantities for enzyme activation, stomatal regulation, and stress tolerance was steadily draining away over the centuries.

The torreya trees themselves reflected the depletion. Leaf concentrations of carbon, nitrogen, and potassium all decreased with tree age, while leaf phosphorus held comparatively steady. That divergence matters because leaf chemistry is a sensitive indicator of what a tree can actually extract from its environment. A falling leaf potassium concentration in the oldest stands suggests the trees could no longer take up enough of the element to maintain the internal levels seen in their younger counterparts, even as they kept growing on the accumulated organic capital of their soils.

Perhaps the most striking result concerned nutrient resorption efficiency, the process by which trees withdraw valuable nutrients from aging leaves before they fall, effectively recycling their own biochemical investments. Resorption efficiencies of nitrogen, phosphorus, and potassium all declined substantially as tree age increased, but the potassium pathway showed by far the largest drop, falling from about three-quarters in the youngest stands to just under a third in the oldest. For a tree, losing the ability to salvage most of the potassium in its leaves represents a fundamental shift in nutrient economy, forcing greater dependence on an increasingly depleted soil pool.

Why Potassium Became the Weak Link in Torreya Trees

The drivers behind these shifts were traced through statistical modeling of soil chemistry. Nitrogen resorption efficiency responded primarily to soil nitrogen availability, specifically the nitrate and ammonium forms plants can absorb directly. Phosphorus and potassium resorption, by contrast, were more sensitive to soil potassium levels and pH. This split suggests different nutrients answer to different environmental levers, and that a one-size-fits-all fertilization strategy would fail to fix the specific bottlenecks emerging in ancient stands.

A network analysis of the pathways revealed that tree age influences nutrient resorption mostly indirectly, through its effects on the elemental balance of soil, leaves, and litter around the torreya trees. Crucially, potassium-related imbalances exerted the most negative influence on resorption efficiency of any factor examined. The implication is that potassium is not merely one nutrient among several running low. It acts as a keystone element whose scarcity destabilizes the balance of nitrogen and phosphorus cycling throughout the whole ecosystem, according to the study's listing on Springer.

This finding resonates with a growing body of global evidence. A 2023 meta-analysis cited in the study highlighted that potassium limitation is far more widespread in terrestrial ecosystems than classical nutrient thinking, long focused on nitrogen and phosphorus, would suggest. Potassium is unusual among macronutrients because it does not form part of any structural organic compound. It exists in plant tissue as a free ion, which means it is easily leached from litter and soils and cannot be locked into stable organic pools the way nitrogen and phosphorus can. Over sixteen centuries of continuous cultivation and harvest, that mobility appears to have worked against the ancient torreya trees.

What Ancient Torreya Trees Teach Conservation

For conservationists, the practical implications are concrete. The authors argue that soil test-based nutrient management, including targeted potassium fertilization and measures to prevent soil acidification, could help sustain the ancient torreya trees, which are both culturally treasured and economically important for their edible nuts. The study also touches on a complication: the region's history of high atmospheric nitrogen deposition, which earlier work on Torreya plantations suggested can blunt the benefits of conventional fertilization. The picture that emerges is one of multiple nutrient stresses compounding one another in the oldest stands.

To be fair, the study has a built-in caveat worth stating. A chronosequence substitutes space for time: no one watched a single grove for sixteen hundred years. The researchers controlled for climate and management traditions across the age groups, which makes the age interpretation credible, but the work still captures one province's torreya tree plantations, and targeted potassium fertilization has yet to be field-tested as a fix. The authors are describing a diagnosis, not yet a cure.

Still, the broader lesson travels far beyond one hillside in China. Ancient trees are not simply younger trees scaled up in time. They occupy a distinct biogeochemical state shaped by centuries of nutrient cycling, and protecting them may require understanding and correcting elemental deficits that only become visible across millennial timescales. As the world's oldest living trees face mounting pressures from climate change and land-use intensification, this research suggests that what lies beneath them, in the slow chemistry of their soils, may matter as much as what threatens them above ground. Explore more tree science on our Plants and Trees topic page, and read how protecting the forest floor helped another logging study hold onto its carbon in this related story.