Seasonal variations in soil respiration, heterotrophic respiration and autotrophic respiration of a wheat and maize rotation cropland in the North China Plain

Determining soil respiration from croplands is necessary for evaluating the global terrestrial carbon budget and how it is altered in future climates. This study explored seasonal characteristics and controlling factors of soil respiration in a typical cropland area in the North China Plain. Total soil respiration (RS) was partitioned into heterotrophic (RH) and autotrophic (RA) components using the root exclusion method. The experiments showed that the seasonal average RS values were 5.25 μmol m−2 s−1 for the wheat growing season and 6.00 μmol m−2 s−1 for the maize growing season. Seasonal average RH and RA values were 3.34 μmol m−2 s−1 and 1.91 μmol m−2 s−1, respectively, for wheat, and were 4.25 μmol m−2 s−1 and 1.75 μmol m−2 s−1, respectively, for maize. The seasonal average ratio of RA to RS (RA/RS) was 36% for wheat and 29% for maize. Over a whole year, RH was the dominant component of RS in both the wheat and maize growing seasons. RH increased exponentially with the average soil temperature collected in the upper 10 cm (TS0-10), with a Q10 value of 1.65. Soil water content (θ) had no discernible influence on RH when θ was between wilting point (θwp) and field capacity (θfc). A value of θ larger than θfc suppressed RH, which can be characterized by a quadratic curve. RA increased exponentially with TS0-10 in both of the wheat and maize growing seasons, and the corresponding Q10 values were 2.69 and 2.85, respectively. However, the temperature dependence of RA in the two crop seasons cannot be explained by a single temperature response curve. Moreover, the RA values for the wheat and maize growing seasons were more sensitive to temperature changes than RH at the study site. Soil water content had no discernible influence on RA in the wheat growing season but suppressed RA when water logging occurred in the maize growing season. However, RA recovered afterwards even when the soil water content was high. Comparisons between wheat respiration values collected at different sites showed that the seasonal average RS, RH and RA all correlate positively with mean air temperature, indicating that air temperature remains a good indicator for variations in soil respiration in different climates.