Thermal sensitivity of soil microbial carbon use efficiency across forest biomes.

Understanding the large-scale pattern of soil microbial carbon use efficiency (CUE) and its temperature sensitivity (CUE T ) is critical for understanding soil carbon-climate feedback. We used the 18 O-H 2 O tracer method to quantify CUE and CUE T along a north-south forest transect. Climate was the primary factor that affected CUE and CUE T , predominantly through direct pathways, then by altering soil properties, carbon fractions, microbial structure and functions. Negative CUE T (CUE decreases with measuring temperature) in cold forests (mean annual temperature lower than 10 °C) and positive CUE T (CUE increases with measuring temperature) in warm forests (mean annual temperature greater than 10 °C) suggest that microbial CUE optimally operates at their adapted temperature. Overall, the plasticity of microbial CUE and its temperature sensitivity alter the feedback of soil carbon to climate warming; that is, a climate-adaptive microbial community has the capacity to reduce carbon loss from soil matrices under corresponding favorable climate conditions.