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 (R-S) was partitioned into heterotrophic (R-H) and autotrophic (R-A) components using the root exclusion method. The experiments showed that the seasonal average R-S values were 5.25 mu mol m(-2) s(-1) for the wheat growing season and 6.00 mu mol m(-2) s(-1) for the maize growing season. Seasonal average R-H and R-A values were 3.34 mu mol m(-2) s(-1) and 1.91 mu mol m(-2) s(-1), respectively, for wheat, and were 4.25 mu mol m(-2) s(-1) and 1.75 mu mol m(-2) s(-1), respectively, for maize. The seasonal average ratio of R-A to R-S (R-A/R-S) was 36% for wheat and 29% for maize. Over a whole year, R-H was the dominant component of R-S in both the wheat and maize growing seasons. R-H increased exponentially with the average soil temperature collected in the upper 10 cm (TS0-10), with a Q(10) value of 1.65. Soil water content (theta) had no discernible influence on R-H when theta was between wilting point (theta(wp)) and field capacity (theta(fc)). A value of theta larger than theta(fc) suppressed R-H, which can be characterized by a quadratic curve. R-A increased exponentially with TS0-10 in both of the wheat and maize growing seasons, and the corresponding Q(10) values were 2.69 and 2.85, respectively. However, the temperature dependence of R-A in the two crop seasons cannot be explained by a single temperature response curve. Moreover, the R-A values for the wheat and maize growing seasons were more sensitive to temperature changes than R-H at the study site. Soil water content had no discernible influence on R-A in the wheat growing season but suppressed R-A when water logging occurred in the maize growing season. However, R-A recovered afterwards even when the soil water content was high. Comparisons between wheat respiration values collected at different sites showed that the seasonal average R-S, R-H and R-A all correlate positively with mean air temperature, indicating that air temperature remains a good indicator for variations in soil respiration in different climates. (C) 2013 Elsevier B.V. All rights reserved.