Browsing by Author "Du, Taisheng"

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    Isotope signature of maize stem and leaf and investigation of transpiration and water transport
    (Elsevier, 2021-03) Wu, Youjie; Du, Taisheng; Wang, Lixin; Earth Science, School of Science
    Stable isotope signature of plant water contains essential information on water transport pathway and plant transpiration, which has been shown to be a powerful tracer in plant physiological and ecological processes. However, stable isotopes fractionation in processes of plant water transport and the relationship between transpiration rate (E) and effective pathway length (L) and their possible mechanisms are still largely mysterious and confusing. Here, we tested stable isotope signature of maize stem and leaf based on anatomical measurements and modeling, and propose a deuterium deviation in leaf water (Δd) to understand variability leaf water isotope enrichment and transpiration. We found isotopes fractionation occurred in maize stems in arid area. Leaf transpiration rate was strongly affected by Δd. The data revealed L has a negative power relationship with E, with a single power function of L = 284.77E−1.02; and the proportional deviation of leaf 18O enrichment 1 − ΔL/ΔE is negatively correlated with E under low E (E < 2.0 mmol m−2 s−1) and, a positively relationship under high E (E > 2.0 mmol m−2 s−1). Suggesting that a pivotal role of effective path length in driving variations in leaf transpiration rate. The deuterium deviation Δd may have great potential to serve as a new diagnostic tool for understanding pathways of water transport in plant. Care should be taken when examining source-water and estimating roots water uptake using the stable isotope method in arid areas, and further study is needed to be carried out and confirm the conclusions across a range of environmental conditions and species.
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    A modified isotope-based method for potential high-frequency evapotranspiration partitioning
    (Elsevier, 2022-02) Yuan, Yusen; Wang, Lixin; Wang, Honglang; Lin, Wenqing; Jiao, Wenzhe; Du, Taisheng; Earth Sciences, School of Science
    To better understand water and energy cycles, numerous efforts to partition evapotranspiration (ET) into evaporation (E) and transpiration (T) have been made over the recent half century. One of the analytical methods is the isotopic approach. The isotopic composition of ET (δET) is a crucial parameter in the traditional isotope-based ET partitioning model, which however, has considerable uncertainty and high sensitivity. Here we proposed a modified T fraction in total ET (FT) calculation using Keeling plot slope (k), the atmospheric vapor concentration (Cv), and the isotopic composition of atmospheric vapor (δv), to avoid the direct use of δET. Following the traditional method, we used the Craig-Gordon model for the isotopic composition of evaporation (δE) and chamber method for the isotopic composition of transpiration (δT) in our modified method. The modified FT calculation method (FT (m)) can be applied at a 15-min time scale using the average values (FTi (mp)) and at a 1 Hz time scale for high-frequency method (FTi). The modified method was verified by both theoretical derivations and field observations. FTi (mp) was equivalent to those using the traditional isotopic method at a 15-min time scale. However, FTi eliminated the highly sensitive parameter δET, and redistributed the sensitivity of δET into three less sensitive parameters. Additionally, FTi has two main advantages. First, the high-frequency method avoids the extrapolation of the Keeling plot regression line intercept. Second, the high-frequency method can produce a 95% confidence interval of FT in a measurement cycle (e.g., 15 min). The calculated confidence interval was different from that of traditional uncertainty analysis. The high-frequency method might be useful when investigating evapotranspiration partitioning under short-term extreme weather events and flush agricultural irrigation.
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    Multiple Methods to Partition Evapotranspiration in a Maize Field
    (2017-01) Wu, Youjie; Du, Taisheng; Ding, Risheng; Tong, Ling; Li, Sien; Wang, Lixin; Department of Earth Sciences, School of Science
    Partitioning evapotranspiration (ET) into soil evaporation E and plant transpiration T is important, but it is still a theoretical and technical challenge. The isotopic technique is considered to be an effective method, but it is difficult to quantify the isotopic composition of transpiration δT and evaporation δE directly and continuously; few previous studies determined δT successfully under a non-steady state (NSS). Here, multiple methods were used to partition ET in a maize field and a new flow-through chamber system was refined to provide direct and continuous measurement of δT and δE. An eddy covariance and lysimeter (EC-L)-based method and two isotope-based methods [isotope combined with the Craig–Gordon model (Iso-CG) and isotope using chamber measurement (Iso-M)] were applied to partition ET. Results showed the transpiration fraction FT in Iso-CG was consistent with EC-L at both diurnal and growing season time scales, but FT calculated by Iso-M was less than Iso-CG and EC-L. The chamber system method presented here to determine δT under NSS and isotope steady state (ISS) was robust, but there could be some deviation in measuring δE. The FT varied from 52% to 91%, with a mean of 78% during the entire growing season, and it was well described by a function of LAI, with a nonlinear relationship of FT = 0.71LAI0.14. The results demonstrated the feasibility of the isotope-based chamber system to partition ET. This technique and its further development may enable field ET partitioning accurately and continuously and improve understanding of water cycling through the soil–plant–atmosphere continuum.
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    Novel Keeling-plot-based methods to estimate the isotopic composition of ambient water vapor
    (EGU, 2020-09) Yuan, Yusen; Du, Taisheng; Wang, Honglang; Wang, Lixin; Earth Sciences, School of Science
    The Keeling plot approach, a general method to identify the isotopic composition of source atmospheric CO2 and water vapor (i.e., evapotranspiration), has been widely used in terrestrial ecosystems. The isotopic composition of ambient water vapor (δa), an important source of atmospheric water vapor, is not able to be estimated to date using the Keeling plot approach. Here we proposed two new methods to estimate δa using the Keeling plots: one using an intersection point method and another relying on the intermediate value theorem. As the actual δa value was difficult to measure directly, we used two indirect approaches to validate our new methods. First, we performed external vapor tracking using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to facilitate explaining the variations of δa. The trajectory vapor origin results were consistent with the expectations of the δa values estimated by these two methods. Second, regression analysis was used to evaluate the relationship between δa values estimated from these two independent methods, and they are in strong agreement. This study provides an analytical framework to estimate δa using existing facilities and provides important insights into the traditional Keeling plot approach by showing (a) a possibility to calculate the proportion of evapotranspiration fluxes to total atmospheric vapor using the same instrumental setup for the traditional Keeling plot investigations and (b) perspectives on the estimation of isotope composition of ambient CO2 (δa13C).