Coupled of carbon and nitrogen mineralization in rhizosphere soils along a temperate forest altitudinal gradient.

Aims: Rhizosphere is a hotspot for soil C and N biogeochemical cycling in terrestrial ecosystems. However, the interaction between soil C and N mineralization remain poorly understood in the rhizosphere soils. This study aimed to identify interactions between soil C and N mineralization in rhizosphere soils and bulk soils at a large scale. Methods: We used the "soil adhering to fine roots after shaking" method to collect paired rhizosphere soils and bulk soils along an altitudinal forest gradient. Soil C mineralization rates (Cmin) and net N mineralization rates (Nmin) were determined with laboratory incubation. Results: We found a significantly positive relationship between Cmin and Nmin in the rhizosphere soils across sites, whereas Cmin was not correlated with Nmin in the bulk soils. Furthermore, soil properties, microbial biomass C (MBC) and extracellular enzyme activities showed substantial paths affecting Cmin and Nmin using structural equation model. The coupling of Cmin and Nmin in rhizosphere soils could be triggered by root-soil interactions, resulting in the higher level of MBC, total organic C of soil, total N of soil, and extracellular enzyme activities. By contrast, the decoupling of Cmin and Nmin in the bulk soils might be attributed to the lower level of MBC and extracellular enzyme activities. Conclusions: Our results demonstrated that soil C and N mineralization coupled in the rhizosphere rather than in the bulk soils. These results suggest that the interaction between soil C and N cycling in rhizosphere are likely to differ from that in bulk soil. [ABSTRACT FROM AUTHOR]