Data from: Differential impacts of nitrogen addition on rhizosphere and bulk-soil carbon sequestration in an alpine shrubland

1. Due to complex root-soil interactions, the responses of carbon (C) dynamics in the rhizosphere to elevated nitrogen (N) deposition may be different from those in bulk soil. However, the potentially different response of C dynamics in the rhizosphere and bulk soils and their contributions to soil C sequestration under N deposition is still not elucidated.

2. We conducted an N addition experiment in an alpine shrubland dominated by Sibiraea angustata located on the eastern Qinghai-Tibet Plateau (QTP). We measured the soil organic C (SOC) contents and density fractions in the rhizosphere and bulk soils in the top 15 cm of mineral soil and then employed a numerical model based on the rhizosphere extent to evaluate how the rhizosphere modulates soil C sequestration under N addition. We also measured the microbial gene abundance and C-acquisition enzyme activities to assess microbial community responses to N addition.

3. The results showed that nitrogen addition had opposite effects on the rhizosphere and bulk-soil C stocks. Specifically, N addition decreased the rhizosphere SOC content through increasing bacterial abundance, β-glucosidase activity, and thus accelerating the loss of free light fraction C (FLF-C). However, N addition increased the bulk-soil C content, which was corresponding with the reduced oxidase activities and the accelerated accumulation of heavy fraction C (HF-C) under N addition. Numerical model analysis showed that the decrease induced by N addition in rhizosphere SOC stock ranged from 0.11 to 3.01 kg C m^-2 as root exudation diffusion distance extended from 0.5 mm to 2 mm, while the corresponding increase in the bulk-soil C stock ranged from 1.91 to 4.08 kg C m^-2. By synthesizing the dynamics of the SOC stocks in these two soil compartments under N addition, the SOC stock at the ecosystem level exhibited an increase in range of 0.73-2.44 kg C m^-2.

4. Synthesis Our results suggest that alpine shrublands on the eastern QTP have great potential for soil C sequestration under N deposition, and the magnitude of the sequestration would depend closely on the responses of rhizosphere microbial C processes and the rhizosphere extent. Our results highlight the importance of integrating rhizosphere processes into land surface models to accurately predict ecosystem functions in the background of elevated N deposition.