Observation and Study on Material and Energy Exchange of Paddy at Different Growth Stages in the Liaohe Delta, Northeast China

Abstract This study utilized observational data from the Panjin Wetland Ecosystem Field Observation Station during January to December 2019 to analyze water, heat, and carbon flux characteristics, as well as radiation balance, at different growth stages of paddy (transplanting, jointing, heading, and maturation) in Panjin. The results show that: (1) The jointing stage exhibited the highest average temperature, while the heading stage experienced the heaviest precipitation, approximately 3.3 times that of other periods. (2) Sensible heat flux followed the order of jointing stage > maturation stage > heading stage > transplanting stage, with negative values at night and positive values during the day. Latent heat flux followed the order of transplanting stage > heading stage > jointing stage > maturation stage, with positive latent heat flux throughout the day. Net ecosystem exchange (NEE) followed the order of transplanting stage > maturation stage > jointing stage > heading stage, with the transplanting stage acting as a carbon source and the heading stage exhibiting the strongest carbon fixation capacity. (3) Solar shortwave radiation dominated during different growth stages of paddy, with net radiation following the order of jointing stage > transplanting stage > heading stage > maturation stage. (4) Latent heat was the dominant energy exchange during different growth stages of paddy. The energy closure ratio was highest in the maturation stage, followed by the jointing stage, transplanting stage, and heading stage. The energy closure ratio in the maturation stage reached 69.63%, indicating good energy closure, while it was only 38.88% in the heading stage, indicating poor energy closure. (5) Sensible and latent heat fluxes generally exhibited positive correlations with environmental factors during different growth stages, while NEE showed a negative correlation. Photosynthetically active radiation and net radiation are identified as key factors influencing sensible heat flux, latent heat flux, and NEE. Evaporation has a significant impact on the latent heat flux. Additionally, air temperature, soil temperature, and vapor pressure deficit also play significant roles.