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

Soil respiration (or CO production) is often determined by measuring CO 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 CO 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 CO, temperature and moisture that were continuously recorded at 0, 8 and 15 cm, and calibrated by measured CO efflux. We then applied the model to calculate CO production and efflux over 2014-2015, and found a strong and similar seasonality in both CO 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 CO production and efflux over short period following rainfall. There were significantly exponential relationships between CO production/efflux and temperature. While straw incorporation significantly increased CO production and efflux, straw incorporation combined with gypsum amendment caused a decrease in CO production and efflux. CO production exceeded CO efflux mainly in the first half year, and annual difference was 33-130 g C m, with larger differences under gypsum amendment. Our study implies that a portion of respired CO is transformed into other forms and stored in saline-alkaline soils in arid land.