[A-CG39] Global Carbon Cycle Observation and Analysis

[ACG39-P10] Testing of Evapotranspiration Partitioning in a Rice Paddy Using Gross Primary Production Estimated from Eddy Covariance

*Hayeon Won^1,2, BoKyeong Kim^1,2, Subin Choi¹, KyeongMin Kim¹, HyunDong Moon^1,2, Hyunhwan Yang¹, Jaeil Cho^1,2 (1.Department of Applied Plant Science, Chonnam National University, Gwangju, Republic of Korea, 2.BK21 FOUR Center for IT-Bio Convergence System Agriculture, Chonnam National University, Gwangju, Republic of Korea)

Keywords:Evapotranspiration, Partitioning, GPP, WUE

Evapotranspiration (ET) is a key process in water exchange between the atmosphere and the land surface, significantly affecting meteorological phenomena and water resource management. In agriculture, understanding water loss due to ET is crucial for effective irrigation. ET consists of soil evaporation and stomatal transpiration, where plants lose water through stomata while assimilating CO2 for photosynthesis. In cropland, water loss occurs as soil moisture from irrigation evaporates. Partitioning ET into evaporation and transpiration not only allows for the evaluation of water use efficiency (WUE) and crop transpiration utilization rates but also provides insight into the relationship between water availability and plant physiological responses. Since water availability regulates stomatal opening and closure, it directly affects gross primary production (GPP). Therefore, considering both the carbon and water cycles is essential. This understanding plays a key role in optimizing crop productivity, improving irrigation efficiency, and developing effective water resource management strategies. This study was conducted through two experiments. First, experiments were performed using a non-weighing lysimeter (NWL) in a temperature gradient chamber under warming conditions, with treatments at ambient air temperature (Ta) and Ta +3℃. Water level variations were used to directly separate and measure evaporation (E) and transpiration (T). As a result, the partitioning characteristics determined by leaf area index (LAI) were not affected by temperature conditions. Second, the in-situ eddy covariance (EC) method was used in a paddy field in Naju to continuously measure ET without disturbing the rice paddy. ET was partitioned using the GTV (GPP-Transpiration-VPD) and FVS (Flux Variance Similarity) methods. The GTV method accounts for the correlation between GPP and T while incorporating VPD, whereas the FVS method utilizes EC-based water vapor and carbon dioxide flux measurements along with a leaf-level WUE algorithm. Both methods are based on the correlation between GPP and T, mediated by stomatal regulation. The GTV and FVS methods were compared based on the partitioning characteristics determined by LAI in the NWL method, enabling a more precise separation of E and T and enhancing the reliability of ET partitioning. The GTV method has only been applied in rice paddies, and it is necessary to analyze when the two methods exhibit similarities or differences depending on meteorological and biological conditions. Additionally, previous FVS studies suggest that accuracy tends to decline when vegetation is sparse and the transpiration ratio is low. Therefore, it is necessary to conduct additional research to develop and validate algorithms to ensure reliable ET partitioning.

Acknowledgement
This work was supported by Korea Environment Industry and Technology Institute (KEITI) through Project for developing an observation-based GHG emissions geospatial information map, funded by Korea Ministry of Environment (MOE) (Project No. RS-2023-00232066, 2023-2027).