Articles | Volume 15, issue 1
Biogeosciences, 15, 115–136, 2018

Special issue: Ecosystem processes and functioning across current and future...

Biogeosciences, 15, 115–136, 2018

Research article 09 Jan 2018

Research article | 09 Jan 2018

Modelling the diurnal and seasonal dynamics of soil CO2 exchange in a semiarid ecosystem with high plant–interspace heterogeneity

Jinnan Gong1, Ben Wang1,2, Xin Jia1,2, Wei Feng2, Tianshan Zha2, Seppo Kellomäki1, and Heli Peltola1 Jinnan Gong et al.
  • 1School of Forest Sciences, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland
  • 2Yanchi Research Station, School of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, China

Abstract. We used process-based modelling to investigate the roles of carbon-flux (C-flux) components and plant–interspace heterogeneities in regulating soil CO2 exchanges (FS) in a dryland ecosystem with sparse vegetation. To simulate the diurnal and seasonal dynamics of FS, the modelling considered simultaneously the CO2 production, transport and surface exchanges (e.g. biocrust photosynthesis, respiration and photodegradation). The model was parameterized and validated with multivariate data measured during the years 2013–2014 in a semiarid shrubland ecosystem in Yanchi, northwestern China. The model simulation showed that soil rewetting could enhance CO2 dissolution and delay the emission of CO2 produced from rooting zone. In addition, an ineligible fraction of respired CO2 might be removed from soil volumes under respiration chambers by lateral water flows and root uptakes. During rewetting, the lichen-crusted soil could shift temporally from net CO2 source to sink due to the activated photosynthesis of biocrust but the restricted CO2 emissions from subsoil. The presence of plant cover could decrease the root-zone CO2 production and biocrust C sequestration but increase the temperature sensitivities of these fluxes. On the other hand, the sensitivities of root-zone emissions to water content were lower under canopy, which may be due to the advection of water flows from the interspace to canopy. To conclude, the complexity and plant–interspace heterogeneities of soil C processes should be carefully considered to extrapolate findings from chamber to ecosystem scales and to predict the ecosystem responses to climate change and extreme climatic events. Our model can serve as a useful tool to simulate the soil CO2 efflux dynamics in dryland ecosystems.

Short summary
By modelling soil CO2 production, transport and surface exchange processes (e.g. biocrust photosynthesis, respiration and photodegradation), we simulated the large variation of soil CO2 emissions from sparsely vegetated dryland ecosystem. Based on the model, we studied the roles of different processes in regulating soil C emissions. The complexity of regulation processes implied possibly high non-linearity of C responses to climatic variation, climate change and extreme climate events.
Final-revised paper