Modelling the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange in a semiarid ecosystem with high plant-interspace heterogeneity

Abstract

<p><strong>Abstract.</strong> This study represents a first attempt to model the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange (<i>F</i><sub>S</sub>) in a dryland ecosystem with a high plant-interspace heterogeneity. The modelling used an integrated process-based approach, in which the CO<sub>2</sub> production, transport and surface exchanges (e.g. biocrust photosynthesis, respiration and photodegradation) are considered simultaneously. The model was parameterized and validated with multivariate data measured during year 2013–2014 in a semiarid shrubland ecosystem in Yanchi, northwestern China. We also investigated the sensitivity of simulated <i>F</i><sub>S</sub> to a set of stand-specific parameters and investigated the relative contribution of different flux components. The model explained reasonably well the two-year dynamics of <i>F</i><sub>S</sub> measured from a non-crusted and two lichen-crusted plots. Simulations showed that the temporal pattern of <i>F</i><sub>S</sub> could deviate from that of the total CO<sub>2</sub> production from rooting-zone soil. Such deviations could be explained by the variations of CO<sub>2</sub> dissolution and the CO<sub>2</sub> exchanges of biocrust during wetting-drying cycles, and the root uptake and transport of dissolved CO<sub>2</sub>. Moreover, the <i>F</i><sub>S</sub> was spatially sensitive to the plant-interspace differences and the variations in root biomass, soil organic matter and pH. These results emphasized that, the processes beyond autotrophic and heterotrophic respirations and the heterogeneities of soil at plant-interspace can strongly affect the <i>F</i><sub>S</sub> dynamics and their climatic sensitivities. Such variability should be carefully considered in extrapolation of findings from chamber to ecosystem level and from seasonal to inter-annual scales. Based on this work, our model can serve as a useful tool to simulate <i>F</i><sub>S</sub> dynamics in dryland ecosystems.</p>