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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 #403810
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: Influence of water use efficiency parameterizations on flux variance similarity-based-partitioning of evapotranspiration

Author
item Wagle, Pradeep
item RAGHAV, PUSHPENDRA - University Of Alabama
item KUMAR, MUKESH - University Of Alabama
item Gunter, Stacey

Submitted to: Ph D Dissertation
Publication Type: Other
Publication Acceptance Date: 10/12/2023
Publication Date: 2/20/2024
Citation: Wagle, P., Raghav, P., Kumar, M., Gunter, S.A. 2023. Influence of water use efficiency parameterizations on flux variance similarity-based-partitioning of evapotranspiration. Ph D Dissertation. Tuscaloosa, Alabama: University of Alabama. 242 p.

Interpretive Summary: Partitioning of evapotranspiration (ET) into evaporation (E, unproductive water use) and transpiration (T, productive water use) has numerous important implications. Several recent studies have reported a good performance of Flux Variance Similarity (FVS)–based ET partitioning method. Despite the high sensitivity of leaf-level water use efficiency (WUE) estimates to intracellular carbon dioxide concentrations (ci) in FVS partitioning, sensitivity analysis of ci parameterizations is lacking. Using high frequency eddy covariance data for wheat (Triticum aestivum L.) and canola (Brassica napus L.), we performed sensitivity analysis of four ci parameterizations (constant_ppm, constant_ratio, and linear and square root functions of vapor pressure deficit) and compared them with the optimized WUE approach with no adjustable parameter. Changing ci parameters resulted in varied partitioned outputs (i.e., T:ET ratios), due to direct impact on WUE estimates and T, for all four WUE algorithms. Three models (constant_ppm, constant_ratio, and optimum) were able to produce expected trends of T:ET ratios during dry and wet periods in both crops. Linear and square root models showed poor performances. The results indicated the potential for using constant_ppm and constant_ratio models for FVS partitioning by continuing to use the commonly used ci in both crops. The optimum model also showed its potential for inter-model comparison, especially in sensitivity analysis, for FVS partitioning in C3 species. Results illustrate that the choice of WUE algorithm and input value for ci parameterization in WUE algorithms for FVS partitioning can lead to large biases in partitioned fluxes.

Technical Abstract: Despite the high sensitivity of water use efficiency (WUE) estimates to intracellular carbon dioxide concentrations (ci) in the Flux Variance Similarity (FVS)-based partitioning method, a systematic analysis of the sensitivity of WUE to ci parameterizations has largely been lacking. Using high-frequency (10 Hz) eddy covariance data for two crop sites: wheat (Triticum aestivum L.) and canola (Brassica napus L.), we performed a sensitivity analysis of four ci parameterizations (constant ci value, constant ci/ca ratio, and ci/ca as square root and linear functions of vapor pressure deficit) and compared them with the optimized WUE approach with no adjustable parameter. The results illustrated the role of ci parameterizations on the evapotranspiration (ET) partitioning results (i.e., transpiration (T) to ET ratios). Notably, constant ci value and constant ci/ca ratio parameterizations for the largest considered ci values (commonly used default values in most previous studies) showed comparable T:ET with the optimized WUE approach. Additionally, all these three models produced reduced T:ET in wet periods and increased T:ET in dry periods. In contrast, square root and linear models were unable to accurately capture expected trends of T:ET for wet and dry periods, and also showed large discrepancies when compared with the optimal WUE approach. The results suggest that optimal parameterizations of ci should be derived in constant ci value and constant ci/ca ratio methods to accurately capture temporal variations of WUE and T:ET. The results also indicate the potential of the optimum model for inter-model comparison, especially in sensitivity analysis, for FVS partitioning in C3 species. This study provides novel insights into the implications of the choice of parameterization on the WUE estimations and partitioning outcomes.