Local soil conditions reshape how trees end their growing season under warming

What is it about?

This study is about why autumn xylem phenology responds to warming in unexpectedly different ways across regions, and how local soil conditions—especially nitrogen and moisture—can override simple temperature effects. Using Northern Hemisphere field observations of autumn xylem growth cessation, we show that higher soil nitrogen can delay the end of cell-wall thickening but advance the termination of cell enlargement, with the advancing effect strongest in humid forests. This counterintuitive pattern suggests that nutrient-rich conditions can amplify growth and water demand, so trees may end the highly water-consuming enlargement phase earlier to avoid seasonal water stress—even in regions typically considered “wet.” Overall, the work reframes autumn phenology as a nutrient–water–temperature coupled process, offers a new lens on drought vulnerability and mortality in humid forests, and highlights autumn cell-enlargement phenology as an early-warning indicator of emerging drought risk under climate warming.

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Why is it important?

Autumn phenology is a key, yet poorly understood, regulator of forest growth, carbon sequestration, and drought vulnerability. This study is important because it challenges the long-standing assumption that warming, when accompanied by sufficient water and nutrients, will universally delay autumn growth processes. Instead, it shows that local soil nitrogen and moisture can fundamentally alter—and even reverse—the response of autumn xylem phenology to rising temperature. By revealing that nutrient-rich conditions can amplify tree water demand and trigger earlier termination of water-intensive xylem cell enlargement—even in humid forests—this work redefines where and when water limitation occurs. It helps explain why severe drought impacts and tree mortality have recently been observed in traditionally wet ecosystems, such as parts of the Amazon, sometimes exceeding those in semi-arid regions. Importantly, the study highlights autumn xylem phenology as a sensitive, process-based early-warning indicator of drought stress, offering a new tool for anticipating forest decline before large-scale mortality occurs. More broadly, it underscores that reliable predictions of forest responses to climate warming require integrating temperature with local nutrient and water constraints, rather than relying on climate variables alone.

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