Seasonality of soil respiration under gypsum and straw amendments in an arid saline-alkali soil

Abstract

Soil respiration (or CO2 production) is often determined by measuring CO2 efflux; however, there are differences between them in saline-alkali soils of arid land. The purpose of this study is to test a hypothesis that CO2 production exceeds efflux in arid saline-alkali soils under organic and gypsum amendments. We conducted a modeling study that was based on a two-year field experiment with four treatments: control, gypsum addition, wheat straw incorporation, and gypsum-straw combination. A diffusion model was forced by soil CO2, temperature and moisture that were continuously recorded at 0, 8 and 15 cm, and calibrated by measured CO2 efflux. We then applied the model to calculate CO2 production and efflux over 2014–2015, and found a strong and similar seasonality in both CO2 production and efflux under all treatments (i.e., highest in summer with one peak in 2014 and two peaks in 2015). Our results showed enhanced CO2 production and efflux over short period following rainfall. There were significantly exponential relationships between CO2 production/efflux and temperature. While straw incorporation significantly increased CO2 production and efflux, straw incorporation combined with gypsum amendment caused a decrease in CO2 production and efflux. CO2 production exceeded CO2 efflux mainly in the first half year, and annual difference was 33–130 g C m−2, with larger differences under gypsum amendment. Our study implies that a portion of respired CO2 is transformed into other forms and stored in saline-alkaline soils in arid land.