Properties of secondary xylem of mature oaks in southwest Germany formed after extreme drought stress in summer 2018

• Published in: Trees, Forests and People (Online) Vol. 5; p. 100097
• Main Authors: Süßel, Florian, Brüggemann, Wolfgang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2021; Elsevier
• Subjects: Drought; Oaks; Tree rings; Tylosis; Wood properties; Xylem; ar1; Xylem; LO; RU; SW; HLUG (now HLNUG); Rbar; EPS; IAEA-CH-7; WUEi; PCA; Tree rings; VPDB; ΨPD; USGS24; Wood properties; LA; NI; Drought; Mglk; Tylosis; WM-550; Oaks
• ISSN: 2666-7193; 2666-7193
• DOI: 10.1016/j.tfp.2021.100097

•Year-ring growth of German oaks decreased after the extreme drought year 2018.•Δ13C values indicate increased WUEi during the drought year.•Xylem vessels of Qu. petraea were filled with tyloses.•PCA of 2019 tree ring and 2018 physiology data separated populations.•Qu. robur populations were separated along the physiology-dominated axis. The effect of the extreme summer drought and heatwave 2018 in Central Europe on wood properties of oaks at four sandy valley river sites (Quercus robur L.) and one south-exposed schist slope (Qu. petraea (Matt.) Liebl.) in the middle Rhine and lower Main valley were studied and compared to well-watered trees from a riparian stand. While properties of the 2018 tree rings mostly resembled those of the previous (wet) year, significant decreases in Δ13C, wood density and ring width occurred in 2019 at most drought-prone sites. In the sandy sites, ring widths correlated with previous-year precipitation from June to August over a 20-year period. In organs formed in 2018, in general, decreasing Δ13C values were obtained in the order leaves, twigs, wood and acorns, with the values from acorns often resembling those from 2019-year rings. The observed changes indicated an increased intrinsic water use efficiency and lack of starch reserve formation during the unprecedented hot and dry summer 2018. Qu. petraea revealed quite different values from Qu. robur (lower Δ13C, wider and denser year rings), but qualitatively showed the same reaction to the drought in 2018, except for an enhanced formation of tyloses in recent-year tree rings.