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) is critical for understanding soil carbon-climate feedback. We used the O-HO tracer method to quantify CUE and CUE along a north-south forest transect. Climate was the primary factor that affected CUE and CUE, predominantly through direct pathways, then by altering soil properties, carbon fractions, microbial structure and functions. Negative CUE (CUE decreases with measuring temperature) in cold forests (mean annual temperature lower than 10 °C) and positive CUE (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.