Soil respiration dynamics and effects of hydrothermal factors and NPP during growing period of maize cropland ecosystem in Songnen Plain, China

The current research on soil respiration components and soil carbon cycling is at the forefront of soil respiration. Currently, the constructed soil respiration rate models are mainly hydrothermal factor models, which lacks consideration of biological factors and understanding of soil respiration component dynamics, and is insufficient to fully describe the role of environmental factors on soil respiration. Therefore, clarifying the dynamics of soil respiration (components) and the effects of hydrothermal and biological factors during the crop growing period is of great significance for the theory and practice of carbon cycling in cropland ecosystems. Based on the data of soil respiration, Eddy covariance (EC) flux, and meteorology, which were observed in 2019 at experimental site during the growth period of maize (Zea mays L.) in the Songnen Plain, China, the dynamics of soil respiration (components) and the effects of hydrothermal factors and NPP during crop growing period were researched by mathematical statistics and carbon balance equation. In maize cropland ecosystem of the Songnen Plain, the daily variation and growing period dynamics of soil respiration rates Rs (Rh, Rr) in each key growing stage showed a unimodal distribution, with the peak of the daily changes mainly occurring in the afternoon and the lowest value mainly occurring before sunrise. The soil respiration rate accelerated with the growth process, and was higher in the vigorous growing period of crops, and then decreased. The average value of Rs was 4.5308 g C m-2 d-1, and the contribution of Rr to Rs was 54.9% during the growing period. Soil hydrothermal factors and NPP had significant effects on soil respiration rate during the growing period, among them, soil surface temperature and NPP played dominant roles, soil temperature sensitivity was highest at 10 cm depth, Q10 was 1.89. The soil respiration rate model with the effect of soil hydrothermal factors and NPP was constructed by the added method, the model was able to express soil respiration rate dynamics, explaining from 52.6 to 57.7% of the Rs variation, compared with the expression result that only considers the hydrothermal factors, the interpretation rate has increased from 9.3 to 13.1%. NPP of the maize cropland ecosystem in 2019 was 1113.51 g C m-2 during crop growing period, C expenditure through soil heterotrophic respiration was 304.93 g C m-2, NEE was- 808.58 g C m-2, the maize cropland ecosystem showed carbon sink. Fully increasing NPP and reducing soil heterotrophic respiration consumption are effective ways to increase NEE of cropland ecosystems, which can optimize the carbon balance of cropland ecosystems.