Pit membranes in bordered pits between neighbouring vessels play a major role inthe entry of air-water menisci from an embolised vessel into a water-filled vessel(i.e., air-seeding). Here, we... Show morePit membranes in bordered pits between neighbouring vessels play a major role inthe entry of air-water menisci from an embolised vessel into a water-filled vessel(i.e., air-seeding). Here, we investigate intervessel pit membrane thickness (TPM)and embolism resistance (P50, i.e., the water potential corresponding to 50% lossof hydraulic conductivity) across a broad range of woody angiosperm species.Data on TPM and double intervessel wall thickness (TVW) were compiled based onelectron and light microscopy. Fresh material that was directly fixated for transmission electron microscopy (TEM) was investigated for 71 species, while non-freshsamples were frozen, stored in alcohol, or air dried prior to TEM preparation for anadditional 60 species. TPM and P50 were based on novel observations and literature.A strong correlation between TPM and P50 was found for measurements based onfreshly fixated material (r = 0.78, P <0.01, n = 37), and between TPM and TVW(r = 0.79, P < 0.01, n = 59), while a slightly weaker relationship occurred betweenTVW and P50 (r = 0.40, P <0.01, n = 34). However, non-fresh samples showed nocorrelation between TPM and P50, and between TPM and TVW. Intervessel pit membranes in non-fresh samples were c.28% thinner and more electron dense thanfresh samples. Our findings demonstrate that TPM measured on freshly fixatedmaterial provides one of the strongest wood anatomical correlates of drought-induced embolism resistance in angiosperms. Assuming that cellulose micro fibrilsshow an equal spatial density, TPM is suggested to affect the length and the shapeof intervessel pit membrane pores, but not the actual pore size. Moreover, theshrinking effect observed for TPM after dehydration and frost is associated withan increase in micro bril density and porosity, which may provide a functionalexplanation for embolism fatigue. Show less
