Modelling the diurnal and seasonal dynamics of soil CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchange in a semiarid ecosystem with high plant–interspace heterogeneity

Jinnan Gong,Tianshan Zha,Wei Feng,Xin Jia,Heli Peltola,Seppo Kellomäki,Ben Wang

doi:10.5194/bg-15-115-2018

Modelling the diurnal and seasonal dynamics of soil CO&lt;sub&gt;2&lt;/sub&gt; exchange in a semiarid ecosystem with high plant–interspace heterogeneity

Jinnan Gong, Tianshan Zha + Show 5 more

Open Access

https://doi.org/10.5194/bg-15-115-2018

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Abstract

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.

Highlights

CO2 exchange between soil and atmosphere constitutes a major carbon (C) loss from terrestrial ecosystems (Raich et al, 2002; Giardina et al, 2014)
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
Our model can serve as a useful tool to simulate the soil CO2 efflux dynamics in dryland ecosystems

Summary

Introduction

CO2 exchange between soil and atmosphere constitutes a major carbon (C) loss from terrestrial ecosystems (Raich et al, 2002; Giardina et al, 2014). It plays an important role in the feedbacks between the global carbon cycle and climate change (Rustad et al, 2000; Giardina et al, 2014; Karhu et al, 2014). The contribution of soil CO2 flux (FS) from those ecosystems to the global C budget is less studied (CastilloMonroy et al, 2011; Gao et al, 2012; Jia et al, 2014). Soil CO2 flux of dryland ecosystems is widely interpreted using temperature-response functions modified by other environmental constraints, e.g. soil water content, abundance of substrates and microbial activities (Curiel Yuste et al, 2007; W. Wang et al, 2014; B. Wang et al, 2014, 2015)

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