Biophysical controls of soil respiration in a wheat-maize rotation system in the North China Plain

- Soil respiration was controlled by leaf area index, soil temperature and moisture in the wheat field.
- Soil respiration was affected by soil temperature and moisture in the maize field.
- Monthly soil respiration of the wheat field was closely linked with photosynthesis.
- At the annual scale, soil respiration accounted for 72% of ecosystem respiration.

Croplands play a vital role in regional carbon budgets. We hypothesized that biophysical factors would be important for soil respiration in a wheat-maize rotation cropping system. Soil CO2 efflux was measured using the closed chamber method, and net CO2 exchange between the cropland and the atmosphere obtained by the eddy covariance technique in a winter wheat-summer maize double cropping system over four years (Oct 2002-Oct 2006). In addition to soil temperature, soil respiration was controlled by leaf area index and soil moisture in the wheat field and soil moisture in the maize field. Temperature sensitivity (Q10) of soil respiration was 2.2 in the wheat and maize growing seasons. In the wheat field, the Q10 value during the sowing-returning green period (4.9) was more than that during the returning green-ripening period (2.0). On a monthly time scale, soil respiration was controlled by gross primary productivity in the wheat field, indicating that soil respiration was coupled with ecosystem photosynthesis. Annual soil respiration was 825 ± 73g C m−2 in the wheat-maize rotation system in 2003-2006. Over a 4-year average, soil respiration was 355 ± 50 g C m−2 in the wheat growing season and 470 ± 67 g C m−2 in the maize growing season, which accounted for 43% and 57% of the annual value respectively. At an annual time scale, soil respiration contributed to 72% of ecosystem respiration in the winter wheat-summer maize double cropping system.