Compounding drought and climate effects disrupt soil water dynamics in grasslands
Summary author: Walter Beckwith
A novel field experiment in Austria reveals that compounding climate conditions – namely drought, warming, and elevated atmospheric carbon dioxide (CO2 ) – could fundamentally reshape how water moves through soils in temperate grasslands. The findings provide new insights into post-drought soil water flow, in particular. Soil water, though a minuscule fraction of Earth's total water resources, plays a critical role in sustaining terrestrial life on Earth by regulating biogeochemical cycles, surface energy balance, and plant productivity. Soils also govern the fate of precipitation, directing it back to the atmosphere via evapotranspiration or into surface and groundwater systems, depending on soil water storage and flow properties, such as soil texture and structure. However, droughts – expected to become more frequent and severe under change – could disrupt these crucial processes. Atmospheric warming may increase evapotranspiration and soil water loss, while elevated atmospheric CO2 could reduce transpiration by narrowing plant stomata and conserving soil moisture. Thus, the combined effects of warming and elevated CO2 can produce complex, albeit poorly understood, hydrological outcomes. Grasslands, which cover 30-40% of Earth's land surface, depend heavily on shallow soil water, making them ideal for studying rootzone ecohydrological dynamics.
Jesse Radolinski et al. conducted a novel deuterium (²H) labeling field experiment in a temperate grassland in Austria to examine how elevated atmospheric CO2, warming, and recurring drought – individually and in combination – affect soil water. Radolinski et al. induced experimental drought conditions and then applied 2H-labeled rainfall under ambient and simulated future climate scenarios. According to the findings, elevated CO2 increased rootzone moisture, while warming reduced soil moisture, with soil water remaining well mixed under most conditions. However, combined summer drought, warming, and elevated CO2 drove grassland plants to conserve water by reducing transpiration, which restricted soil water flow to large, rapidly draining pores, limiting mixing with smaller pores. The findings suggest that future drought conditions could fundamentally alter soil water dynamics by limiting post-drought soil water flow and grassland vegetation water use.
Journal
Science
Article Title
Drought in a warmer, CO2-rich climate restricts grassland water use and soil water mixing
Article Publication Date
17-Jan-2025
New study reveals how climate change may alter hydrology of grassland ecosystems
UMD researcher finds shallow groundwater mixes less with rainwater and plants conserve more following drought in warmer, high-CO2 conditions
University of Maryland
image:
Panoramic view of the ClimGrass Facility in Styria, Austria which subjects a temperate grassland to individual and combined atmospheric warming (+3°C) and CO2 enrichment (+ 300 ppm), and recurring drought.
view moreCredit: Markus Herndl
New research co-led by the University of Maryland reveals that drought and increased temperatures in a CO2-rich climate can dramatically alter how grasslands use and move water. The study provides the first experimental demonstration of the potential impacts of climate change on water movement through grassland ecosystems, which make up nearly 40% of Earth’s land area and play a critical role in Earth’s water cycle. The study appears in the January 17, 2025, issue of the journal Science.
“If we want to predict the effects of climate change on Earth’s water resources, we need data showing how the hydrologic cycle will respond at a small scale where we can define mechanisms, but that just hasn’t been available,” said Jesse Radolinski corresponding author of the study, a post-doctoral research associate in the UMD Department of Environmental Science & Technology who began the work at the University of Innsbruck. “Our experiments found that under summer drought conditions, and higher air temperatures that are expected under a future with elevated CO2, two things change fundamentally: One, the structural properties of the soil in the root zone change so that water flows differently than we expected, and two, these altered climate conditions and soil properties cause the plants to access water differently.”
Currently, new rainfall tends to linger in the root zone where it mixes with existing soil water (i.e., previous rainfall) before percolating into local streams and rivers. Radolinski said this study suggests that under future climate conditions, intense rainfall may move more quickly through the soil into local water bodies, interacting less with this stored water and potentially bringing nutrients and pollutants with it. In addition, plants subjected to these future drought conditions conserve more water, releasing less back to the atmosphere through transpiration. That could mean less atmospheric cooling, triggering a feedback loop of more drought and more warming.
Radolinski and his colleagues conducted their experiment with the University of Innsbruck in open plots in an Austrian grassland. They simulated six different climate conditions by manipulating air temperature and CO2 levels, and introducing recurring drought with large, automatically deployed shelters that prevented natural rainfall from reaching the plots. When they simulated rainfall, they used water with a traceable isotope of hydrogen called deuterium, and then tracked its path through the plants and the soil.
Their results showed that after recurring droughts in plots with elevated CO2 and warming, the structure of pores in the soil changed so that older water could remain locked in smaller pores, while newer water flowed into larger pores that drained more quickly. In addition, the plants were effective at accessing the most readily available soil moisture and conserved water loss by releasing less to the atmosphere through transpiration. This may help plants adapt to water stress under future drought conditions, though more research is needed to tease out the effects on growth.
The study reveals that soil and plant water interactions could be much more complex than previously thought, with significant consequences for the ability of ecosystems to withstand and recover from drought. These insights will be critical in informing conservation strategies and managing ecosystems in a rapidly changing climate.
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Radolinski completed his fellowship as a post-doctoral research associate in the laboratory of Dr. Gurpal Toor in January, 2025. The study was an international collaboration co-led by researchers at the University of Innsbruck.
Automatic rainout shelters engaging to suppress rainfall from an approaching storm during experimental drought period at the ClimGrass Facility in Styria, Austria.
- Measuring water stable isotopic signatures of vapor in transpiration chambers to aid inferring the source of grassland water use.
- Measuring water stable isotopic signatures of vapor in transpiration chambers to aid inferring the source of grassland water use.
Credit
Camille Halais
Camille Halais
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