Soil microbial respiration in forest ecosystems along a north-south transect of eastern China: Evidence from laboratory experiments

Soil microbial respiration (MR) is a key process controlling the soil-atmosphere CO2 flux, and is widely studied at individual sites. Yet its spatial variation and underlying mechanism at larger spatial scales are still poorly understood, limiting our estimates of the carbon cycle in terrestrial ecosystems and its feedbacks to climate change. Here, a novel incubation experiment based on the mean annual temperature of soil origin sites along a 4,200 km north-south forest transect of eastern China was conducted to investigate the spatial variations in MR. MR showed a hump-shaped relationship with latitude and peaked around 32 degrees N, which coincided exactly with the ecotone of subtropical and temperate forests. Climate, soil physicochemical and microbial traits explained 56.1% of the total variations in MR across the transect, whereas explained 77.4% and 34.6% in tropical and subtropical versus temperate region, respectively. Soil physicochemical properties were consistently more important in controlling the MR's variation than other variables. Specifically, soil organic carbon was the most important factor in regulating the MR's variation across the transect, whereas its significance decreased when scaling down to tropical and subtropical regions. The mean annual temperature turned into the best indicator of MR in tropical and subtropical forests, whereas the combination of soil organic carbon with total nitrogen concentrations primarily regulated the variations in MR in temperate region. Collectively, our study showed a non-linear latitudinal pattern of soil MR and revealed the diverged controlling factors and mechanisms of MR in different climatic regions. These findings can potentially improve our capacity to predict the soil CO2 flux in Earth system models and the feedbacks to climate change.