Carbon sequestration in salt affected and alkaline soils under cotton in Tarim oasis (China)

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The main objective of the project is the elucidation of the process that leads to CO2 flux into the soils. This phenomenon has been reported on oasis cotton fields in Xinjing, China especially at night. We assume that physicochemical processes (e. g. recrystallyzation as pedogenic carbon, higher solution in cool soil water) than biological processes (e.g. incorporation in soil microorganisms or plant roots are responsible for this CO2 flux into soil. To explore the process causing CO2 flux into soil, CO2 production and transport in soil as well as increased dissolution in the soil water and recrystallization of pedogenic CaCO3 will be investigated. Analysis of CO2 fluxes will be conducted in the field on plots with and without cotton plants. For complete assessment of soil CO2 production and transport and to testify the soil surface CO2 efflux described by Fick’s fist law, soil surface CO2 efflux will be measured continuously both by chamber and by eddy covariance methods. Additionally, a small solid-state CO2 sensor will be used to measure continuously soil CO2 concentrations at depths of 0 cm, 5 , 15 , 20 , 30 , 50 , 80 and 100 cm. Other soil physical characteristics and biotic factors influencing soil CO2 production and transport will be measured simultaneously.Isotopic labeling with 14CO2 in the laboratory and with 13CO2 in the field will help to understand mechanisms of CO2 fixation. Application of 14CO2 under defined environmental conditions (temperature, moisture, day/night) to microcosms with and without plants will enable us to trace 14C in soil water, soil air, plants, pedogenic carbonates, microorganisms and the air above the soil. Considering the elucidated mechanisms of CO2 flux into and out of the soil, field experiments with 13CO2 will be conducted. Measurements of CO2 concentrations and isotopic composition in all compartments will enable us create a model which elucidates the phenomenon of CO2 fixation in soils. Keywords: Soil CO2 production, Soil CO2 transport, Oasis cotton field, carbon balance, pedogenic carbonates