TY  - JOUR
A1  - Süßel, Florian
A1  - Brüggemann, Wolfgang
T1  - Tree water relations of mature oaks in southwest Germany under extreme drought stress in summer 2018
T2  - Plant stress
N2  - Mature oak stands of different tree height at four sandy valley river sites (Quercus robur) and one south-exposed schist slope (Qu. petraea) in the middle Rhine and lower Main valley were studied from early summer 2017 (normal wet year) until the end of 2018 (extremely hot and dry year). Tree water relations (ΨPD, RWC, sap flow rates) were monitored together with soil water relations, LAI and leaf chl content. In two sandy sites with presumed continuous capillary water access from the groundwater aquifer, sap flow rates of the large trees (30 m) and estimated canopy conductance decreased to about 50% of the maximum value in the course of summer 2018, but recovered in autumn. At two other sites, with smaller trees (14–24 m) and presumed interrupted capillary water access during mid-summer 2018, sap flow rates and canopy conductance broke down completely and trees shed a large proportion of leaves in summer. In one of these sites, ΨPD decreased (reversibly) to -4 MPa, one of the lowest values reported in the literature for central Europe, and tree damage resulted not only in extreme leaf shedding, but also in susceptibility to uprooting (in 2 out of 5 measured trees) by thunderstorm gusts in autumn 2018. At the schist slope site, where oaks reached the lowest height and stand density of all sites, sap flow rates remained similar to the values found at the presumed capillary-water supplied sandy sites, indicating access to rock fissure water even at the peak of the drought period. Our findings corroborate the prediction from vegetation modelling that several Qu. robur stands in the Rhine-Main valleys will be prone to severe forest dieback in the forthcoming decades.
KW  - Drought
KW  - Groundwater
KW  - Oaks
KW  - Sap flow
KW  - Water relations
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/63121
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-631215
SN  - 2667-064X
N1  - This work was funded by the research funding programme “LOEWE – Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz" of Hesse's Ministry of Higher Education, Research, and Arts and by the Leibniz Association (Berlin) through the collaboration project “South Hesse Oak Project” between Senckenberg – Leibniz Institution for Biodiversity and Earth System Research and Goethe University Frankfurt.
VL  - 1
IS  - art. 100010
SP  - 1
EP  - 9
PB  - Elsevier
CY  - Amsterdam
ER  -