As the global climate continues to evolve, its impact on ecosystems, particularly plant life, becomes increasingly evident. Plants, equipped with ingenious mechanisms to endure drought stress, play a crucial role in maintaining ecological balance. Yet, a critical question looms: Are plants more inclined to defend themselves against dry air or dry soil? This debate, rife among climate scientists, holds significance in determining effective strategies for preserving resilient plant life amid a changing climate.
Kaighin McColl, an assistant professor in the Department of Earth and Planetary Sciences and the John A. Paulson School of Engineering and Applied Sciences, led a team that recently published groundbreaking research in Nature Water. The study challenges prevailing notions, suggesting that plant drought-defense mechanisms, involving the closure of tiny leaf pores called stomata to limit photosynthesis and conserve water, are more likely triggered by dry soil than dry air.
This revelation contradicts prior research, which posited that plants close stomata in response to dry air rather than dry soils. McColl and his team, however, approached the inquiry with skepticism, emphasizing that correlation does not necessarily imply causation. McColl stated, “When plants close their stomata, that could actually be causing the air to get drier, rather than the other way around.”
To test their opposing hypothesis, the researchers utilized a natural laboratory devoid of plants—the barren salt flats of Utah and Nevada. Drawing on data from these salt flats, the team replicated earlier studies that correlated air dryness with moisture flux, attributing these values to plant stomatal closure. Surprisingly, their calculations aligned closely with previous findings, prompting the realization that an alternative explanation was needed due to the absence of plants in the salt flats.
In this plant-free environment, where evaporation responds solely to soil dryness, McColl and lead author Lucas Vargas Zeppetello found that plant responses to humidity scarcity may have been overstated in prior studies. Instead, the research suggests that plants are more attuned to dry soil, a stressor known to reduce transpiration and photosynthesis.
The implications of this discovery are profound: Soil dryness emerges as a more pivotal factor than air dryness in influencing global plant ecosystems. Vargas Zeppetello emphasized the relevance of these findings for future water projections, stating, “Our findings put emphasis on projections for water in the future. People talk about consensus on climate change, but that really has to do with global temperatures. There’s much less of a consensus on what regional changes to the water cycle are going to look like.”
As the scientific community grapples with the complexities of climate change, this research underscores the need for a nuanced understanding of how plants respond to environmental stressors. The implications of soil moisture on plant resilience could reshape strategies for mitigating the impact of climate change on global ecosystems, highlighting the importance of considering regional variations in the water cycle for comprehensive climate projections.