Hierarchical Bayesian Synthesis of Soil Respiration across Seven Desert Ecosystems

Quantifying soil carbon fluxes is critical to understanding the global carbon cycle and feedbacks to climate change. Although deserts cover more than 30% of the terrestrial biosphere, they are thought to play minor roles in the global carbon cycle. However, the magnitude of soil CO₂ efflux ("soil respiration") and the factors controlling it in desert ecosystems are not well understood. The dominant paradigm, based mainly on mesic ecosystems, is that soil respiration is primarily controlled by a ubiquitous response of soil microorganisms and plant roots to temperature. Water limitations, however, may override temperature influences in deserts. We test this by evaluating the temperature responses of soil respiration in seven deserts across North America and Greenland, spanning 66°C. We synthesized this large dataset within a hierarchical Bayesian framework that allowed us to quantifying important sources of uncertainty (e.g., measurement method calibrations, date within desert random effects, correlations between parameters describing site-specific responses) and obtain estimates of desert-specific parameters related to soil respiration. After accounting for water availability, a common peaked temperature response emerges. Similar to mesic ecosystems, soil respiration increases with temperature below 30°C, but it also declines with hotter (>35°C) conditions and is insensitive to temperatures exceeding 45°C. Compared to mesic ecosystems, the temperature sensitivity of soil respiration is remarkably low. The temperature sensitivity and magnitude of soil respiration are controlled by short- and long-term (antecedent) water availability, but desert-specific antecedent effects likely reflect differences in climatic regimes and belowground components. This synthesis suggests that the unique behavior of deserts is important for understanding the global carbon cycle.