Soil respiration insensitivity under combined extremes: Insights from laboratory experiments

Abstract:

Sensitivity of soil respiration to emerging combined extreme events (i.e., heatwave and drought) is yet poorly understood. In particular, the release of carbon dioxide (CO₂) into the atmosphere, due to plant root and rhizomicrobial activities, which is a major flux that regulates the terrestrial carbon balance. In this work, we explore plant-microbe-soil interactions under controlled climate conditions using a millifluidic setup that enables direct 2D visual observations of hydration condition and oxygen content, the two factors primarily controlling root and microbial respiration in the root zone. We observe that the passive movement of water between different soil parts via plant roots, the so-called root hydraulic redistribution, sustains the soil respiration under such combined extremes, which leads to a strong reduction in land’s carbon sink potential. This root-mediated control on soil fluxes provides new insights into hidden mechanisms not accounted for by large-scale Earth system models.