Atmospheric and Soil Drought Interact Subadditively to Constrain Pasture Grass Productivity

Plant responses to severe drought arise from the interaction of soil water deficits and atmospheric dryness, yet atmospheric dryness is rarely manipulated in drought studies. In a controlled-environment experiment with the pasture grass Dactylis glomerata, soil and atmospheric drought reduced productivity subadditively. These declines were associated with biochemical limitations, increased respiratory costs, and reduced water-use efficiency, driven by their interactions, highlighting the need to incorporate VPD–soil drought interactions into climate projections.