Depth-dependent regulations of soil priming effects along a 2000 km grassland transect

Abstract

Global change may change plant carbon input, which may in turn accelerate or retard the mineralization of soil organic matter (SOM), a phenomenon known as priming effect. However, deep soil priming effect on large geographic scale is poorly understood, hindering a complete understanding of the response of whole-soil carbon dynamics to plant carbon input. Across a 2000 km grassland transect in Inner Mongolia, China, this study showed that soil priming effects at 0-200 cm depth varied systematically with climate and soil properties. The intensity of priming effect varied with depth. Averaged across 10 sites along the transect, glucose addition increased native SOM decomposition by 5.1% in surface soil (0-10 cm), while decreased it by 12.9% and 25.7% in middle (30-50 cm) and deep (150-200 cm) soils, respectively. Interestingly, the regulating factors of priming at different depths were significantly different. The priming effect in surface soil was primarily regulated by SOM stability represented by content of soil minerals and (clay+silt) %, whereas that in middle soil was mainly regulated by soil substrates, SOM stability and soil pH, and that in deep soil was mainly controlled by soil substrates. This study demonstrates distinct controls of the priming effect across soil depths at the regional scale, and contributes to improving our understanding of how whole-soil carbon dynamics respond to global change.