Global Change Factors Regulate the Apparent Thermal Acclimation of Soil Respiration: A Meta-Analysis

As the climate warms, the initial enhancement of soil respiration (Rs) induced by short-term warming has the potential to decrease in magnitude over time due to the apparent thermal acclimation of Rs. However, the existence and magnitude of this kind of thermal acclimation are highly uncertain, partly because the response of Rs to warming is regulated by multiple environmental factors acting simultaneously [e.g., drought, precipitation, nitrogen deposition and elevated atmospheric CO2] rather than by temperature alone. Although extensive manipulative field studies and a few meta-analyses have been conducted to determine the responses of Rs to a single global change factor, the interactive effects of multiple environmental factors on warming remain unknown. In this study, we performed a meta-analysis of 82 multifactor studies to examine the regulatory effect of four main global change factors on the thermal response of Rs to warming. Our results showed that each global change factor exhibited distinct influences on Rs when occurring simultaneously with warming. Elevated CO2 and precipitation largely enhanced the C-climate feedback in the context of warming; however, drought strongly promoted the apparent thermal acclimation of Rs. Nitrogen and warming had an additive effect on Rs. Additionally, the duration of manipulation might be critical in assessing the responses of Rs to global change factors because biotic responses to environmental change may vary over time. Our study demonstrated that after initially being enhanced by warming in the short term, Rs continuously recovered to previous levels—or even decreased—under long-term warming due to apparent thermal acclimation. We therefore suggest that global change experimental studies should focus more on the combined effects of warming with other global change factors. Additionally, long-term studies are needed to fully understand the interactions between warming, Rs, and other ecosystem limitations (e.g., C substrate depletion, C quantity and quality, nutrient availability, and changes in microbial communities and/or physiological modification).