Soil Physics, Not Plant Genetics, Identified as Primary Limiting Factor in Drought Resistance

ETH Zurich researchers discover that soil capillary forces, not plant traits, limit water uptake during drought. Learn why breeding programs have struggled.

By: AXL Media

Published: Mar 23, 2026, 4:56 AM EDT

Source: Information for this report was sourced from ETH Zurich

Defying Gravity Through Negative Water Potential

To survive, land plants must transport water from deep within the earth to their highest leaves, a process that requires working against the constant pull of gravity. This biological feat is achieved through "negative water potential," a form of internal tension that allows herbs, shrubs, and trees to act as organic suction pumps. For decades, the scientific community has debated whether the limits of this suction were determined by the plant's own vascular architecture or by external environmental factors. A new collaborative effort has finally provided a definitive answer, placing the burden of limitation on the soil itself.

The Invisible Grip of Capillary Soil Forces

Research led by Professor Andrea Carminati of ETH Zurich indicates that the primary bottleneck in water uptake occurs within the microscopic pores of the soil. As soil dries, the capillary and viscous forces holding water in these pores increase exponentially. When the soil water potential drops below -1.5 megapascals, the tension required to extract moisture becomes greater than what the plant can safely generate. This physical threshold acts as an external brake on the plant’s hydraulic system, regardless of the species' individual biological efficiency or root strength.

Stomatal Regulation: A Survival Balancing Act

Plants manage this external tension through stomata—highly sensitive valves on the underside of their leaves. According to Professor Tim Brodribb of the University of Tasmania, these valves are the plant's primary defense against "dying of thirst." When soil tension becomes too high, the stomata close to conserve internal moisture. However, this closure triggers a secondary crisis: starvation. Closed stomata prevent the intake of carbon dioxide, halting the production of sugar molecules and slowing growth. The study suggests that the behavior of these tiny valves is ultimately dictated by the physics of the soil below rather than the atmosphere above.