Drought, Climate Shift Disrupt Grassland Soil Water

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.