Browsing by Author "Boeckx, Pascal"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Causes and consequences of pronounced variation in the isotope composition of plant xylem water
    (European Geosciences Union, 2020-10) De Deurwaerder, Hannes P. T.; Visser, Marco D.; Detto, Matteo; Boeckx, Pascal; Meunier, Félicien; Kuehnhammer, Kathrin; Magh, Ruth-Kristina; Marshall, John D.; Wang, Lixin; Zhao, Liangju; Verbeeck, Hans; Earth Sciences, School of Science
    Stable isotopologues of water are widely used to derive relative root water uptake (RWU) profiles and average RWU depth in lignified plants. Uniform isotope composition of plant xylem water (δxyl) along the stem length of woody plants is a central assumption of the isotope tracing approach which has never been properly evaluated. Here we evaluate whether strong variation in δxyl within woody plants exists using empirical field observations from French Guiana, northwestern China, and Germany. In addition, supported by a mechanistic plant hydraulic model, we test hypotheses on how variation in δxyl can develop through the effects of diurnal variation in RWU, sap flux density, diffusion, and various other soil and plant parameters on the δxyl of woody plants. The hydrogen and oxygen isotope composition of plant xylem water shows strong temporal (i.e., sub-daily) and spatial (i.e., along the stem) variation ranging up to 25.2 ‰ and 6.8 ‰ for δ2H and δ18O, respectively, greatly exceeding the measurement error range in all evaluated datasets. Model explorations predict that significant δxyl variation could arise from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in δxyl emerge between individuals that differ only in sap flux densities or are monitored at different times or heights. This work shows a complex pattern of δxyl transport in the soil–root–xylem system which can be related to the dynamics of RWU by plants. These dynamics complicate the assessment of RWU when using stable water isotopologues but also open new opportunities to study drought responses to environmental drivers. We propose including the monitoring of sap flow and soil matric potential for more robust estimates of average RWU depth and expansion of attainable insights in plant drought strategies and responses.
  • Thumbnail Image
    Item
    Isotopic evidence for oligotrophication of terrestrial ecosystems
    (Nature, 2018) Craine, Joseph; Elmore, Andrew J.; Wang, Lixin; Aranibar, Julieta; Bauters, Marijn; Boeckx, Pascal; Crowley, Brooke E.; Dawes, Melissa A.; Delzon, Sylvain; Fajardo, Alex; Fang, Yunting; Fujiyoshi, Lei; Gray, Alan; Guerrieri, Rossella; Gundale, Michael J.; Hawke, David J.; Hietz, Peter; Jonard, Mathieu; Kearsley, Elizabeth; Kenzo, Tanaka; Makarov, Mikhail; Marañón-Jiménez, Sara; McGlynn, Terrence P.; McNeil, Brenden E.; Mosher, Stella G.; Nelson, David M.; Peri, Pablo L.; Roggy, Jean Christophe; Sanders-DeMott, Rebecca; Song, Minghua; Szpak, Paul; Templer, Pamela H.; Van der Colff, Dewidine; Werner, Christiane; Xu, Xingliang; Yang, Yang; Yu, Guirui; Zmudczyńska-Skarbek, Katarzyna; Earth Sciences, School of Science
    Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δ15N) from more than 43,000 samples acquired over 37 years, here we show that foliar N concentration declined by 9% and foliar δ15N declined by 0.6–1.6‰. Examining patterns across different climate spaces, foliar δ15N declined across the entire range of mean annual temperature and mean annual precipitation tested. These results suggest declines in N supply relative to plant demand at the global scale. In all, there are now multiple lines of evidence of declining N availability in many unfertilized terrestrial ecosystems, including declines in δ15N of tree rings and leaves from herbarium samples over the past 75–150 years. These patterns are consistent with the proposed consequences of elevated atmospheric carbon dioxide and longer growing seasons. These declines will limit future terrestrial carbon uptake and increase nutritional stress for herbivores.