Intervessel pit membrane thickness as a key determinant of embolism resistance in angiosperm xylem

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 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 NaturalisPlant science