Browsing by Author "Wu, Youjie"

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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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    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.