EGU General Assembly 2020
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How do meteorological variables and topography control species-specific water uptake strategy along a forested hillslope?

Ginevra Fabiani1,2, Daniele Penna2, and Julian Klaus1
Ginevra Fabiani et al.
  • 1Luxembourg Institute of Science and Technology, Luxembourg
  • 2Department of Agriculture, Food, Environment and Forestry, University of Florence, Florence, Italy

In the face of current global warming conditions, temperate forest ecosystems are expected to be strongly affected by temperature increase and more frequent and intense water shortage. This leads to severe stress for forest vegetation in many temperate systems. Therefore, understanding the vegetation water use in temperate forests is urgently needed for more effective forest management strategies. Root water uptake (RWU) is a species-specific trait (tree physiology and root architecture) and its spatio-temporal patterns are controlled by a range of site-specific (e.g., topography, geology, pedology) and meteorological factors (e.g., temperature, soil humidity, rainfall.

In the present study, we use stable water isotopologues as ecohydrological tracers combined with continuous measurement of hydrometeorological (weather variables, groundwater levels, soil moisture, streamflow) and physiological (sap flow, radial stem growth) parameters to investigate the spatio-temporal dynamics of water uptake for beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl) trees along a hillslope in a Luxemburgish catchment.

Fortnightly field campaigns were carried out during the growing season (April-October) 2019 to sample water from xylem, soil water at different depths, groundwater, stream water, and precipitation. Soil water isotopic composition and xylem water were extracted via cryogenic distillation. Grab sampling was performed for the other water pools. The isotopic composition was determined through laser spectroscopy and mass spectrometry (for xylem samples only).

From preliminary results, the isotopic composition of xylem water shows a marked seasonal variability suggesting a plasticity in RWU or a change in the isotopic composition of the water pools over the growing season. Moreover, beech and oak trees exhibit different uptake strategies when water supply is low. Within the range of observed groundwater variation topography does not play a statistically significant role on RWU.

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-6954, agnese aguzzoni, 06 May 2020

    Dear dr. Fabiani,

    the differentiation between RWU strategies of the two tree species is well explained by the comparison of the d-excess, as presented in your results. 

    Since I'm also working on similar topics, I would like to ask some details about methodological aspects. How was the xylem collected? From which tree organ was the xylem extracted through cryogenic vacuum distillation?

    many thanks,


    • AC1: Reply to CC1, Julian Klaus, 06 May 2020

      Thank you for your comment. We extraced a wood core from the stem and extracted the water cryogenically.

      • AC2: Reply to AC1, Daniele Penna, 06 May 2020

        Hi Agnese, thank you for your question.

        Julian and I are replying instead of Ginevra because she is in the field today (mobility restrictions apply and she got the permission for this day only).

        In addition to Julian's reply, I can add that Ginevra collected wood cores using a Pressler corer. She removed the bark with cambium and phloem, collected the xylem, and transferred it into 30-ml glass vials sealed with caps and Parafilm. Then she extracted water through the cryogenic vacuum distillation (basically the same equipment you have in your institute).

        By the way, I'm familiar with your interesting work in apple orchards in the Venosta Valley and we can talk about this later, if you wish.



        • CC2: Reply to AC2, agnese aguzzoni, 06 May 2020

          Dear Julian, dear Daniele,

          thank you for your answer and the information that you shared.

          Yes, I indeed worked on the water isotope project in Val Venosta last summer. I'm now considering different strategies to extract water from tree shoots, in addition to the CVD, to compare the isotope ratio of different water compartments of the shoots. Thank you for your help, we can definetely discuss about that.

          best regards,