Functional xylem characteristics associated with drought‐induced embolism in angiosperms

Abstract

Summary Hydraulic failure resulting from drought‐induced embolism in the xylem of plants is a key determinant of reduced productivity and mortality. Methods to assess this vulnerability are difficult to achieve at scale, leading to alternative metrics and correlations with more easily measured traits. These efforts have led to the longstanding and pervasive assumed mechanistic link between vessel diameter and vulnerability in angiosperms. However, there are at least two problems with this assumption that requires critical re‐evaluation: (1) our current understanding of drought‐induced embolism does not provide a mechanistic explanation why increased vessel width should lead to greater vulnerability, and (2) the most recent advancements in nanoscale embolism processes suggest that vessel diameter is not a direct driver. Here, we review data from physiological and comparative wood anatomy studies, highlighting the potential anatomical and physicochemical drivers of embolism formation and spread. We then put forward key knowledge gaps, emphasising what is known, unknown and speculation. A meaningful evaluation of the diameter–vulnerability link will require a better mechanistic understanding of the biophysical processes at the nanoscale level that determine embolism formation and spread, which will in turn lead to more accurate predictions of how water transport in plants is affected by drought.

The Response of Beech (Fagus sylvatica L.) Populations to Climate in the Easternmost Sites of Its European Distribution

“…Furthermore, the growth reduction is even more severe when VPD and other climatic factors (like SM or temperature) thresholds are exceeded [ 63 ]. This finding complements the above results and has a solid physiological background, considering higher VPD declines stomatal conductance and increases the transpiration rates, with higher risks of water loss, hydraulic failure, and growth reduction [ 53 , 61 , 62 , 64 ]. Another possible reason for this drought-induced growth pattern can be related to beech xylem architecture, a diffuse-porous wood exhibiting a significant legacy effect after drought and displaying susceptibility to water stress [ 64 , 65 , 66 ] and VPD [ 63 ].…”

“…This finding complements the above results and has a solid physiological background, considering higher VPD declines stomatal conductance and increases the transpiration rates, with higher risks of water loss, hydraulic failure, and growth reduction [ 53 , 61 , 62 , 64 ]. Another possible reason for this drought-induced growth pattern can be related to beech xylem architecture, a diffuse-porous wood exhibiting a significant legacy effect after drought and displaying susceptibility to water stress [ 64 , 65 , 66 ] and VPD [ 63 ]. Compared with other broadleaf species, beech displays an increased sensibility to drought [ 28 , 53 , 67 ], being more exposed and vulnerable to future climate change [ 18 , 56 , 63 ] and losing its competitive advantages in this context [ 28 ].…”

Ageing-induced shrinkage of intervessel pit membranes in xylem of Clematis vitalba modifies its mechanical properties as revealed by atomic force microscopy

“…Differences in pit membranes thickness across organs have been found, for instance, in Acer pseudoplatanus ( Kotowska et al., 2020 ), but these differences are much smaller than those caused by a gradual shrinkage process over time. Also, we have shown in another study that pit membranes thickness is largely unrelated to conduit dimensions ( Lens et al., 2022 ). There is also published evidence that pit membranes in Vitis vinifera plants cultivated in Israel undergo a 50% shrinkage within a single growing season ( Sorek et al., 2021 ).…”

Hydraulic tradeoffs underlie enhanced performance of polyploid trees under soil water scarcity

“…Our comparisons showed no differences in vessel size between triploids and tetraploids, suggesting that increases in ploidy confront anatomical limitations of vessel width expansion. Larger vessel diameters associate with the enhanced hydraulic efficiency of polyploids, which at the same time conflicts with embolism vulnerability (Sperry et al ., 2008), although the relationship between vessel diameter and vulnerability is still under debate (reviewed by Lens et al ., 2022). Despite vessel size differences, triploids exhibited a lower xylem porosity in the leaves and stems, whereas diploids showed higher leaf and stem porosity; xylem of the tetraploids had an intermediate phenotype, less porous in the leaves, but relatively porous in the stem.…”