Abstract

Microbial release of CO 2 from soils to the atmosphere reflects how environmental conditions affect the stability of soil organic matter (SOM), especially in massive organic-rich ecosystems like the peatlands and grasslands of the Qinghai-Tibetan Plateau (QTP). Radiocarbon ( 14 C) is an important tracer of the global carbon cycle and can be used to understand SOM dynamics through the estimation of time lags between carbon fixation and respiration, often assessed with metrics such as age and transit time. In this study, we incubated peatland and grassland soils at four temperature (5, 10, 15 and 20 degrees C) and two water-filled pore space (WFPS) levels (60 % and 95 %) and measured the 14 C signature of bulk soil and heterotrophic respired CO 2 . We compared the relation between the Delta 14 C of the bulk soil and the Delta 14 CO 2 of respired carbon as a function of temperature and WFPS for the two soils. To better interpret our results, we used a mathematical model to analyse how the calculated number of pools, decomposition rates of carbon ( k ), transfer ( alpha ) and partitioning ( gamma ) coefficients affect the Delta 14 C bulk and Delta 14 CO 2 relation, with their respective mean age and mean transit time. From our incubations, we found that 14 C values in bulk and CO 2 from peatland were significantly more depleted (old) than from grassland soil. Our results showed that changes in temperature did not affect the Delta 14 C values of heterotrophic respired CO 2 in either soil. However, changes in WFPS had a small effect on the 14 CO 2 in grassland soils and a significant influence in peatland soils, where higher WFPS levels led to more depleted Delta 14 CO 2 . In our models, the correspondence between Delta 14 C, age and transit time highly depended on the internal dynamics of the soil ( k , alpha , gamma and number of pools) as well as on model structure. We observed large differences between slow and fast cycling systems, where low values of decomposition rates modified the Delta 14 C values in a non-linear pattern due to the incorporation of modern carbon ( 14 C bomb) in the soil. We concluded that the stability of carbon in the peatland and grassland soils of the QTP depends strongly on the direction of change in moisture and how it affects the rates of SOM decomposition, while temperature regulates the number of fluxes. Current land cover modification (desiccation) in Zoige peatlands and climate change occurring on the QTP might largely increase CO 2 fluxes along with the release of old carbon to the atmosphere potentially shifting carbon sinks into sources.

Published in

Biogeosciences
2024, Volume: 21, number: 5, pages: 1277-1299
Publisher: COPERNICUS GESELLSCHAFT MBH

SLU Authors

• Sierra, Carlos

  • Department of Ecology, Swedish University of Agricultural Sciences
    
  • Max Planck Institute for Biogeochemistry

UKÄ Subject classification

Ecology
Soil Science


Publication identifier

DOI: https://doi.org/10.5194/bg-21-1277-2024

Permanent link to this page (URI)

https://res.slu.se/id/publ/129276