PNNL

Abstract

Soil respiration, the soil-to-atmosphere flux of CO2, is a dominant but uncertain part of the carbon cycle, even after decades of study. This review focuses on the last two decades of progress in understanding Rs from laboratory incubations, surveys key developments of in situ ecosystem-scale Rs observations and manipulations, synthesizes Rs meta-analyses and global flux, and discusses the most compelling challenges and opportunities for the future. Increasingly sophisticated lab experiments have yielded insights about the interaction between heterotrophic respiration, microbial dynamics, substrate supply, and enzymatic kinetics, while novel studies have applied incubation-based analyses across space and time. Using rapidly-improving measurement approaches, both observational and manipulative field-based experiments have improved our understanding of the integrated effect of environmental change and disturbance on Rs. The rise of freely-available observational databases has powered a generation of syntheses, meta-analyses, and new constraints on and understanding of the global Rs flux. Key challenges for the field include expanding Rs measurements, experiments, and opportunities to historically under-represented communities and ecosystems; reconciling independent estimates of global respiration fluxes and trends; testing the power of machine learning models; and continuing the field’s tradition of exploring diverse mechanisms and ecosystems using novel experimental approaches.