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.