Responses of soil respiration in non-growing seasons to environmental factors in a maize agroecosystem, Northeast China

Based on continuous three-year measurements (from 2004 to 2007) of eddy covariance and related environmental factors, environmental controls on variation in soil respiration (R (s)) during non-growing season were explored in a maize agroecosystem in Northeast China. Our results indicated that during non-growing seasons, daily R (s) was 1.08-4.08 g CO(2) m(-2) d(-1), and the lowest occurred in late November. The average R (s) of non-growing season was 456.06 +/- 20.01 g CO(2) m(-2), accounting for 11% of the gross primary production (GPP) of the growing season. Additionally, at monthly scale, the lowest value of R (s) appeared in January or February. From the beginning to the end of non-growing season, daily R (s) tended to decrease first, and then increase to the highest. There was a significant quadratic curve relationship between R (s) and soil temperature at 10 cm depth when soil temperature was more than 0A degrees C (P < 0.001), with the explaining ratio of 38%-70%. When soil water content was more than 0.1 m(3) m(-3), soil moisture at 10 cm depth was significantly parabolically correlated with R (s) (P < 0.001), explaining the rate of 18%-60%. Based on all the data of soil temperature of more than 0A degrees C, a better model for R (s) was established by coupling soil temperature and moisture, which could explain the rate of up to 53%-79%. Meanwhile, the standard error of regression estimation between the values of prediction and observation for R (s) could reach 2.7%-11.8%. R (s) in non-growing season can account for 22.4% of R (s) in growing season, indicating that it plays a critical role in assessing the carbon budget in maize agroecosystem, Northeast China.