Temperature response of soil respiration largely unaltered with experimental warming

Abstract

The respiratory release of carbon dioxide (CO₂) from soil is a major yet poorly understood flux in the global carbon cycle. Climatic warming is hypothesized to increase rates of soil respiration, potentially fueling further increases in global temperatures. However, despite considerable scientific attention in recent decades, the overall response of soil respiration to anticipated climatic warming remains unclear. We synthesize the largest global dataset to date of soil respiration, moisture, and temperature measurements, totaling >3,800 observations representing 27 temperature manipulation studies, spanning nine biomes and over 2 decades of warming. Our analysis reveals no significant differences in the temperature sensitivity of soil respiration between control and warmed plots in all biomes, with the exception of deserts and boreal forests. Thus, our data provide limited evidence of acclimation of soil respiration to experimental warming in several major biome types, contrary to the results from multiple single-site studies. Moreover, across all nondesert biomes, respiration rates with and without experimental warming follow a Gaussian response, increasing with soil temperature up to a threshold of ∼25 °C, above which respiration rates decrease with further increases in temperature. This consistent decrease in temperature sensitivity at higher temperatures demonstrates that rising global temperatures may result in regionally variable responses in soil respiration, with colder climates being considerably more responsive to increased ambient temperatures compared with warmer regions. Our analysis adds a unique cross-biome perspective on the temperature response of soil respiration, information critical to improving our mechanistic understanding of how soil carbon dynamics change with climatic warming.

Keywords: biome; climate change; experimental warming; soil respiration; temperature sensitivity.

Fig. 1.

Ln respiration (µmol C⋅m⁻²⋅s⁻¹) as a function of soil temperature (°C) across biome types. Data are instantaneous measurements from control (blue circles) and warmed (red circles) treatments, with best fit regression lines fitted through control and warmed values (for coefficients, see Table 1). Temperature sensitivity in control versus warmed plots was not significantly different, except in desert and boreal forest biomes (Table 1). Note that y axis scales are all equal, except for desert, which had lower respiration rates compared with all other biomes (SI Appendix, Fig. S4). For partial regression plots of respiration on temperature and moisture, see SI Appendix, Fig. S7.

Fig. 2.

Conceptual diagram of instantaneous delta respiration (∆R) and temperature (∆T) response between warmed (red symbols) and control (blue symbols) treatments on a given day of measurements at the lower end of the temperature range (<25 °C). Circles represent sampling date in spring, whereas stars represent sampling date in summer. (A) All nondesert biomes, except boreal forests. Despite the increase of respiration with warming on a given day of measurements, the temperature response function (the dashed line) across the different colors (the warming effect) is similar to that across the different symbols (the seasonal temperature variation). (B) Boreal forests. Warmed plots (dashed line) had lower sensitivity compared with control plots (solid line). However, no significant differences in the y intercept were observed. (C) Desert. Warmed plots (dashed line) had a lower y intercept but higher sensitivity compared with control plots (solid line). (D) Temperate forest. Despite displaying similar temperature sensitivities, y intercepts of warmed plots (dashed line) were marginally (P = 0.06) lower than control plots (solid line). Delta response was always calculated as warmed value minus control value.

Fig. 3.

Difference in respiration (µmol C⋅m⁻²⋅s⁻¹) between warmed and control plots normalized by degree of warming (∆T, °C), binned by amount of soil desiccation with warming (soil moisture content warmed plots divided by soil moisture content control plots) across the entire dataset. x axis values <1 indicate warmed plots have less moisture available than control plots. y axis values <0 indicate that respiration rates were lower from warmed plots, despite warmer soil temperatures. Respiration data were not log transformed. Delta respiration was always calculated as warmed values minus control values.