Comparison of the partitioning of evapotranspiration – numerical modeling with different isotopic models using various kinetic fractionation coefficients
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In the context of a warming climate and dry conditions, aggravating water shortages, research on partitioning total evapotranspiration (ET) into soil evaporation (E) and plant transpiration (T) is needed.
Methods and aims
Recently, using the oxygen isotope ratio as a tracer has proved to be a valuable way to better partition ET. In this study, we carefully considered the process of heavy water fractionation during the transpiration process, and specifically, we modified the kinetic fractionation coefficient (αk2) of transpiration, based on previous formulations used to estimate it.
Our results show that, for the hourly and daily mean data set, both the isotopic–steady–state (ISS) and non–steady–state (NSS) assumptions for δ18O of leaf water (δL,b) provided a good fit with observed δL,b when using the modified αk2. In contrast, using αk2 values traditionally assigned led to significant deviations from observed δL,b (p < 0.05), potentially influencing ET partitioning results. On diurnal time scales, the percent contribution of T to total ET (FT) is sensitive to different model assumptions and different formulations to estimate αk2. The modeled FT, assuming NSS conditions and using the modified αk2 value, led to the best agreement with observed values. In contrast, on longer time scales (days), using the ISS assumption to partition ET is adequate, as the NSS assumption could introduce more complexities and uncertainties.
Our study demonstrates that the stable isotope technique is a promising utility for quantitatively partitioning ET. To more accurately estimate FT, we also call on a better description of the nature of αk2 of transpiration.
KeywordsEvapotranspiration Non–steady–state Oxygen isotopes Partitioning Transpiration
This study was supported by the National Natural Science Foundation of China (No.41430747), the National Science Fund for Distinguished Young Scholars (No.41401013), and the Beijing Municipal Education Commission (CEFF–PXM2018_014207_000024).
Yonge Zhang designed and performed the experiment. Yonge Zhang analysed the data and wrote the manuscript. Lihua Chen, Guodong Jia contributed significantly to data analysis, manuscript preparation and practice of experiment. Xinxiao Yu revised the paper and finished the submission.
- Baldocchi DD, Ryu Y (2011) A synthesis of forest evaporation fluxes – from days to years – as measured with eddy covariance. In: Forest Hydrology and Biogeochemistry: Synthesis of Past Research and Future Directions, Ecological Studies 216. Springer, Netherlands, Dordrecht, pp. 101–116Google Scholar
- Cernusak LA, Barbour MM, Arndt SK, Cheesman AW, English NB, Field TS, Helliker BR, Phillips MMH, Holtum JAM, Kahmen AF, McInerney A, Munksgaard NC, Simonin KA, Song X, Williams HS, West JB, Farquhar GD (2016) Stable isotopes in leaf water of terrestrial plants. Plant Cell Environ 39:1087–1102CrossRefPubMedGoogle Scholar
- Fan SJ, Lin WS, Su XH, Chen XY, Ma SQ (1999) Study on the application of Richardson number’s stability classifying schemes of the surface layer over coastal reign. J Trop Meteorol 15:370–375Google Scholar
- Jia JB (2016) Eco-hydrological process and mechanism analysis on forests in Beijing mountainous area. Thesis for doctor degree, Beijing Forestry UniversityGoogle Scholar
- Kahmen K, Simonin KP, Tu KP, Merchant A, Callister A, Siegwolf R, Dawson TE, Arndt SK (2008) Effects of environmental parameters, leaf physiological properties and leaf water relations on leaf water delta 18O enrichment in different Eucalyptus species. Plant Cell Environ 31:738–751CrossRefPubMedGoogle Scholar
- Lou YH (2016) Research of using isotope in partitioning forestry ecosystem evapotranspiration. Thesis for master degree, Beijing Forestry University.Google Scholar
- Rothfuss Y, Braud I, Moine LN, Biron P, Durand JL, Vauclin M, Bariac T (2012) Factors controlling the isotopic partitioning between soil evaporation and plant transpiration: assessment using a multi–objective calibration of Si SPAT–Isotope under controlled conditions. J Hydrol 442:75–88CrossRefGoogle Scholar
- Song X, Barbour MM, Farquhar GD, Vann DR, Helliker BR (2013) Transpiration rate relates to within– and across–species variations in effective path length in a leaf water model of oxygen isotope enrichment. Plant Cell Environ 36:1338–1351Google Scholar
- Wang LX, Caylor KK, Villegas JC, Barrongafford GA, Breshears DD, Huxman TE (2010) Partitioning evapotranspiration across gradients of woody plant cover, assessment of a stable isotope technique. Geophys Res Lett 37:232–256Google Scholar
- Wen XF, Zhang SC, Sun XM, Yu GR (2008) Recent advances in H2O enrichment in leaf water. J Plant Ecol 32:961–966Google Scholar
- Xiao Q, Ye WJ, Zhu Z, Chen Y, Zheng HL (2005) A simple non–destructive method to measure leaf area using digital camera and Photoshop software. Chin J Ecol 24:711–714Google Scholar
- Yu GR, Wang QF (2010) Ecophysiology of plant photosynthesis, Transpiration, and Water Use, ed. Li Y, Chen SS, Science press, Beijing.Google Scholar
- Zhou Y, Grice K, Chikaraishi Y, Stuartwilliams H, Farquhar GD, Ohkouchi N (2011) Temperature effect on leaf water deuterium enrichment and isotopic fractionation during leaf lipid biosynthesis, results from controlled growth of C3 and C4 land plants. Phytochemistry 72:207–213CrossRefPubMedGoogle Scholar
- Zou WA, Jiang B, Gu LH (2015) Measurement of Soil Moisture Constants. Journal of China Hydrology 35:62–66Google Scholar