Biotic and abiotic controls on the diel and seasonal variation in soil respiration and its components in a wheat field under long-term nitrogen fertilization

Characterization of the dynamics of soil respiration (Rs) and its components under long-term nitrogen (N) fertilization is necessary to understand the mechanisms that regulate soil carbon (C) emissions. We continuously monitored Rs and its components (heterotrophic respiration (Rh) and autotrophic respiration (Ra)) for 3 years in farmland planted with winter wheat that had been fertilized with N for 10 years to investigate the seasonal and diurnal responses of Rs and its components under different N fertilization rates. The seasonal dynamics of Rs and its components were regulated by biotic factors (leaf area index and photosynthesis) and abiotic factors (soil temperature (ST) and moisture). N addition altered the Rh-to-Rs ratio and resulted in different Rs responses. Moderate N addition increased the C efflux, but excess N fertilization caused no significant change in Rs compared to the treatment without N. Diel Rs and ST are decoupled in farmland. Higher Rs was observed when the temperature increased, which demonstrates the hysteresis effect. N fertilization increased the peak Rs values in the diurnal pattern. N addition changed the seasonal and diurnal patterns of Rs by regulating both biotic and abiotic factors, and Rs did not linearly increase with the N addition rate.