Soil water availability and branch age explain variability in xylem safety of European beech in Central Europe

Abstract

Xylem embolism resistance has been identified as a key trait with a causal relation to drought-induced tree mortality, but not much is known about its intra-specific trait variability (ITV) in dependence on environmental variation. We measured xylem safety and efficiency in 300 European beech (Fagus sylvatica L.) trees across 30 sites in Central Europe, covering a precipitation reduction from 886 to 522 mm year−1. A broad range of variables that might affect embolism resistance in mature trees, including climatic and soil water availability, competition, and branch age, were examined. The average P50 value varied by up to 1 MPa between sites. Neither climatic aridity nor structural variables had a significant influence on P50. However, P50 was less negative for trees with a higher soil water storage capacity, and positively related to branch age, while specific conductivity (Ks) was not significantly associated with either of these variables. The greatest part of the ITV for xylem safety and efficiency was attributed to random variability within populations. We conclude that the influence of site water availability on P50 and Ks is low in European beech, and that the high degree of within-population variability for P50, partly due to variation in branch age, hampers the identification of a clear environmental signal.

Summer drought exposure, stand structure, and soil properties jointly control the growth of European beech along a steep precipitation gradient in northern Germany

“…On the other hand, beech as a species adapted to cool and moist temperate climates shows signs of poor acclimation to summer water deficits, as the species was found to increase leaf size and also stand leaf area (leaf area index) with a reduction in precipitation (Meier & Leuschner, 2008; Weithmann et al, 2021), exposing it to elevated transpiration rates at drier sites. Moreover, the beech trees showed no significant decrease in sun‐canopy branch xylem vulnerability to embolism with a reduction in precipitation (unchanged P50 value), that is, no signs of increasing hydraulic safety upon decreasing water availability (Weithmann et al, 2022). Since the studied trees did not show major crown dieback even after the severe 2018/2019 hot drought, we assume that drought‐induced hydraulic failure, which has caused foliage reduction and crown damage in Central European beech forests mainly on shallow soils (Arend et al, 2022), was not a key factor driving the growth decline.…”

Functional xylem characteristics associated with drought‐induced embolism in angiosperms

“…Furthermore, temporal variation in ‘native’ embolism (daily or seasonal) or the high‐pressure flushing of stems with water before taking an initial hydraulic measurement is known to affect the shape of a vulnerability curve (Domec et al ., 2006; Jacobsen et al ., 2007; Hacke et al ., 2014). Also branch age, growth rate and the number of growth rings may affect the vulnerability curve (Olson et al ., 2018; Pratt et al ., 2020; Weithmann et al ., 2022). In summary, mean vessel diameter does not seem to be a good proxy for drought‐induced embolism, although vessel diameter could have an indirect effect via vessel length and interconnectivity.…”

The Role of the Intraspecific Variability of Hydraulic Traits for Modeling the Plant Water Use in Different European Forest Ecosystems

“…Most models describe the plant vascular factor by lumping the entire system into a single term (Fatichi et al., 2016), omitting the large variability of the forest ecosystems related to tree species and age (Weithmann et al., 2022). This is the case for k max that is a key plant hydraulic trait contributing to the control of the water transport capacity of vegetation (Eamus et al., 2016).…”

“…These results illustrate the effective role of k max in constraining the water use at sites with seasonal water limitations (i.e., FR‐Pue and ES‐Alt). The maximum hydraulic conductance is a parameter highly influenced by plant segment age (Weithmann et al., 2022) and local environmental conditions rather than genetics (Hochberg et al., 2018; Lu et al., 2022). However, the complex interactions between environmental conditions and individual species made it difficult to identify individual environmental drivers for temperate tree species such as Acer platanoides L., Carpinus betulus L., and Tilia cordata Mill (Fuchs et al., 2021).…”

“…The response of species response of hydraulic conductance to contrasting soil conditions is not fixed among species where Fraxinus ornus L. had shown a strong sensitivity to soil dryness (Gortan et al, 2009) while other species such as Pinus sylvestris are not affected by such soil gradients (Jackson et al, 1995). The high environmental plasticity has been documented for F. sylvatica (Weithmann et al, 2022) pointing out the age of the plant segments as the principal driver defining the hydraulic conductance. This characteristic is represented by the range of k max values observed for F. sylvatica and Q. ilex (Figure S5 in Supporting Information S1).…”