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

该项目的主要目标是阐明导致二氧化碳流入土壤的过程。据报道，中国新疆的绿洲棉田出现了这种现象，特别是在夜间。我们认为，物理化学过程（如作为成土碳的再结晶，在凉爽的土壤水中更高的溶液）比生物过程（如在土壤微生物或植物根系中的掺入）对这种进入土壤的二氧化碳通量负责。为了探索CO2进入土壤的过程，将研究CO2在土壤中的生产和运输以及土壤水中溶解增加和成土CaCO3的再结晶。将在种植棉花和不种植棉花的田间地块上进行二氧化碳通量分析。为了全面评估土壤CO2的产生和运输，并验证菲克第一定律所描述的土壤表面CO2外排，将采用室法和涡动相关法连续测量土壤表面CO2外排。此外，一个小型固态二氧化碳传感器将用于连续测量深度为0厘米、5、15、20、30、50、80和100厘米的土壤二氧化碳浓度。同时测量影响土壤CO2生产和运输的其他土壤物理特性和生物因子。在实验室用14CO2和在野外用13CO2进行同位素标记将有助于了解二氧化碳固定的机制。在规定的环境条件下（温度、湿度、白天/夜晚），将14CO2应用于有或没有植物的微观世界，将使我们能够在土壤水、土壤空气、植物、成土碳酸盐、微生物和土壤上方空气中追踪14C。考虑到已阐明的CO2进出土壤的机制，将进行13CO2的田间试验。对所有隔间的二氧化碳浓度和同位素组成的测量将使我们能够建立一个模型，阐明二氧化碳在土壤中的固定现象。关键词：土壤CO2生产，土壤CO2运输，绿洲棉田，碳平衡，成土碳酸盐

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