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ARS Home » Plains Area » El Reno, Oklahoma » Oklahoma and Central Plains Agricultural Research Center » Livestock, Forage and Pasture Management Research Unit » Research » Publications at this Location » Publication #406705

Research Project: Integrated Agroecosystem Research to Enhance Forage and Food Production in the Southern Great Plains

Location: Livestock, Forage and Pasture Management Research Unit

Title: Partitioning of evapotranspiration in C3-C4 mixed tallgrass prairies using FVS, MREA, and CEC methods

item Wagle, Pradeep
item RAGHAV, PUSPHENDRA - University Of Alabama
item KUMAR, MUKESH - University Of Alabama
item SCANLON, TODD - University Of Virginia
item Northup, Brian
item Moffet, Corey
item Gunter, Stacey
item XIAO, XIANGMING - University Of Oklahoma

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/28/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Several methods viz. Flux Variance Similarity (FVS), Modified Relaxed Eddy Accumulation (MREA), and Conditional Eddy Covariance (CEC) have been developed to partition evapotranspiration (ET) into transpiration (T) and evaporation (E) using high-frequency eddy covariance (EC) data. The FVS method uses different approaches for parametrizing intercellular carbon dioxide concentrations (ci) to calculate water use efficiency (WUE, only input). In FVS, some ci parameterization approaches (i.e., constant ci and constant ci/ca ratio) allow for C3 or C4 options and adjustable ci. However, MREA, CEC, and the optimum (i.e., optimized WUE approach) in FVS do not require prior approximations of ci or C3 and C4 species. The performance of MREA, CEC, and three ci parameterization approaches in FVS, along with sensitivity analysis and dynamic ci parameterizations for constant value and constant ratio, was evaluated in two differently managed (grazed vs. hay harvest) C3-C4 mixed tallgrass prairies, which were dominated by warm season C4 grasses. The CEC method produced the highest rate of partitioning solutions, followed by the MREA and FVS methods. The T:ET ratios from MREA and CEC followed similar temporal dynamics, but with relatively larger magnitudes of T:ET ratios than those from FVS throughout the year. For CEC and MREA methods, many half-hourly T:ET ratios were equal to 1 (i.e., 100% T), while the minimum E was around 10-15% for FVS. As a result, the T:ET ratios produced by MREA and CEC may have been slightly higher (by 10-15%) at seasonal and annual scales compared to those obtained from FVS. The T:ET ratios from constant value and constant ratio FVS methods were the same (within 1-2%) at both annual and seasonal scales, regardless of whether they were calculated using a C4 parameterization throughout the year or a dynamic C3-C4 parameterization. Greater agreement among the partitioning methods was found when the correlation coefficient ('qc) between carbon (c) and water vapor (q) concentrations was between -0.1 and 0.1 (i.e., a balance between stomatal and non-stomatal exchange). Overall, significant variations in T:ET ratios were observed across the methods when stomatal ('qc <-0.8) and non-stomatal ('qc >0.8) fluxes dominate. Overall, this study provides insights into the similarities and differences in ET partitioning results from approaches that rely upon high-frequency analysis of eddy covariance data.