Rare pits, large vessels and extreme vulnerability to cavitation in a ring‐porous tree species

Abstract

Summary• The rare pit hypothesis predicts that the extensive inter-vessel pitting in large early-wood vessels of ring-porous trees should render many of these vessels extremely vulnerable to cavitation by air-seeding. This prediction was tested in Quercus gambelii.• Cavitation was assessed from native hydraulic conductivity at field sap tension and in dehydrated branches. Single-vessel air injections gave air-seeding pressures through vessel files; these data were used to estimate air-seeding pressures for inter-vessel walls and pits.• Extensive cavitation occurred at xylem sap tensions below 1 MPa. Refilling occurred below 0.5 MPa and was inhibited by phloem girdling. Remaining vessels cavitated over a wide range to above 4 MPa. Similarly, 40% of injected vessel files air-seeded below 1.0 MPa, whereas the remainder seeded over a wide range exceeding 5 MPa. Inter-vessel walls averaged 1.02 MPa air-seeding pressure, similar and opposite to the mean cavitation tension of 1.22 MPa. Consistent with the rare pit hypothesis, only 7% of inter-vessel pits were estimated to air-seed by 1.22 MPa.• The results confirm the rare pit prediction that a significant fraction of large vessels in Q. gambelii experience high probability of failure by air-seeding.

Embolism resistance as a key mechanism to understand adaptive plant strategies

“…This seems contradictory, but what we do know is that sugars and ions from living xylem and phloem cells are involved [58,[60][61]. This is demonstrated by amongst others girdling experiments [38,58] and the observed transport of water and solutes between phloem and xylem [62].…”

“…However, while the link between pit quantity per vessel and vulnerability to embolism is demonstrated in some angiosperm groups [37], it is lacking in others [22]. Opponents of the rare pit hypothesis use the quantity of intervessel pits per vessel to explain why long-vesseled species usually show vulnerable embolism rates [37][38]. The vulnerability of large vessels, however, is the subject of contradictory opinions.…”

Xylem embolism refilling and resilience against drought‐induced mortality in woody plants: processes and trade‐offs

“…Although still implicit and invasive to a certain degree, hydraulic conductivity measures directly the consequence of embolism, and the technique has been the basis for early descriptions of the Table 1 Study cases on xylem refilling published since 2013, divided by biome and woody plant species. Source references are: (1) Leng et al (2013); (2) Zwieniecki et al (2013); (3) Ooeda et al (2016); (4) Ogasa et al (2013); (5) Umebayashi et al (2016); (6) Martorell et al (2014); (7) Christman et al (2012); (8) Choat et al (2015); (9) Laur and Hacke (2014); (10) Mayr et al (2014); (11) Christensen-Dalsgaard et al (2014); (12) Rolland et al (2015); (13) Ganthaler and Mayr (2015); (14) Trifilo et al (2015); (15) Savi et al (2016); (16) Klein et al 2016;(17) Li et al (2016); (18) Numbers in parentheses indicate the reference number of the respective study in the reference list. The observed changes in embolism level for each species are in Fig.…”

Investigations Concerning Cavitation and Frost Fatigue in Clonal 84K Poplar Using High-Resolution Cavitron Measurements

“…Drought-induced cavitation is caused by the high xylem tension attributed to water stress. The high tension in the sap forces air bubbles into functional conduits from neighboring embolized ones through shared pit membranes (Jarbeau et al, 1995;Sperry et al, 1996;Stiller and Sperry, 2002;Christman et al, 2012) according to an air-seeding mechanism Cochard et al, 1992). Hence, the continuity of water flow is disrupted due to cavitation.…”