Root hydraulic redistribution underlies the insensitivity of soil respiration to combined heat and drought

Abstract

The release of CO2 from the soil into the atmosphere, due to soil respiration, is a major, yet poorly understood flux that regulates the terrestrial carbon balance. In particular, the apparent insensitivity of soil respiration to emerging combined extreme events of heatwave and drought makes terrestrial ecosystems likely to shift from being carbon sinks to sources. Limited understanding of the interactions underlying this response represents one of the key sources of uncertainty in forecasts of atmospheric CO2. Here, we explore plant–microbe–soil interactions under heat and drought using a millifluidic setup that enables direct observations of hydration and oxygen content (the primary factors controlling soil respiration) in the root zone. Our observations reveal movement of water between soil regions via roots (termed root hydraulic redistribution), creating soil respiration hotspots and becoming a carbon source under combined heat and drought.