%0 Journal Article %1 Sperry_Sullivan_92 %A Sperry, J. S. %A Sullivan, J. E. M. %D 1992 %J Plant Physiology %K bibtex-import, citeulikeExport diameter, droughtbolism, freezebolism, snowgumpapermaybe %P 605--613 %T Xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse porous and conifer species %U http://www.plantphysiol.org/cgi/content/abstract/100/2/605 %V 100

@article{Sperry_Sullivan_92, added-at = {2019-03-31T01:14:40.000+0100}, author = {Sperry, J. S. and Sullivan, J. E. M.}, biburl = {https://www.bibsonomy.org/bibtex/28e9cac619cbebdad92ebe2796e3f6380/dianella}, citeulike-article-id = {1524060}, citeulike-linkout-0 = {http://www.plantphysiol.org/cgi/content/abstract/100/2/605}, comment = {(private-note): large early-wood vessels (2.8*10^-9m^3) in oak were most vulnerable to embolism by freezing, small vessels in Populus and Betula were intermediate (approximately 7*10^-11M^3) and tracheids in conifers (about 3*10^-13) were most resistant. The same trend was found within a stem: embolism by freeze-thawing occurred preferentially in wider conduits. "the water stress response was not correlated with conduit volume; previous work indicates it is a function of interconduit pit membrane structure. These guys also plotted vessel diameter size classes and then the percent of the sum of r^4. Branches were dehydrated to a known xylem tension (once they were cut! Surely there's a better way!), then put in bags and frozen over night in a -20oC freezer. Freezing occurred at -10oC. Thawed to 20oC over 90min in their bags. Hypothesised that conduit volume should be proportional to dissolved gas content and therefore bubble size. Diameter was calculated as the equivalent circle diameter for transverse lumen areas ( like what I'm going to do). They used all conduits in size classes that contributed more than 20\% to calculate the hyreaulically weighted average for the volume calculation. Used paint infiltration method to determine vessel lengths. (zimmermann and Jeje 22) Assumed a relationship between length and diameter as measured previously. Staining with safranan dye to see functional and non-functional conduits. Negative pressure used rather than positive pressure to minimise lateral flow of dye. No correlation between freeze-thaw embolism and drought-induced embolism vulnerability. In drought experiments, pressures causing significant embolism were only just higher than those experienced in the field during the growing season. Cavitation during freeze-thaw cycles might rehydrate the stem by releasing water from the conduits (*is this where the water goes? I don't think so!!) The theoretical equation -2T/r thing doesn't actually hold true if you assume volume affects available gas. Even when you assume that bubbles freeze out for every diameter-long segment tension at embolism is still an order of magnitude greater. There is no evidence that xylem sap wouldn't be fully saturated with air (7) But it's likely that lots of bubbles would freeze out, rather than just the one per conduit. " Not all air dissolved in the xylem sap may freeze out as bubbles if it can diffuse ahead of the ice into adjacent air spaces (2). This is predicted to occur only at slow freezing rates (less than 2.5ums-1 (11)) and only if freezing proceeds towards an embolised vessel or other sort of air/water boundary. However, freezing seems to occur centripetally (10,20) therefore, escape of air by this mechanism may be unlikely regardless of the freezing rate.. Another assumption of the equation is that no air redissolves on thawing when tensions might be momentarily reduced. This might be the least valid of assumptions. There would be a steep concentration gradient and might be elevated xylem pressures due to the expansion of water during freezing (\~{}8\%) The drop in tension would be most pronounced with rapid freezing rates and where water isn't allowed to get away from the ice (high resistance to flow away) As long as transpiration is minimal, these pressures wouldn't decrease to the prefreezing value until everything's thawed. The symplast and its conductance seems to be rather important: if it lets the water away, pressure increase might not redissolve bubbles. On the other hand, if water from embolised vessels can travel through the symplast to relieve tension in other neighbouring vessels, it might be good at redissolving. ---=note-separator=--- (private-note)All species except A. lasiocarpa responded differently to the freeze-thaw and water-stress treatments (Fig. 3), suggesting that the two treatments induce cavitation by different mechanisms. There was also no correlation between vulnerability to the two different treatments. For example, Quercus was the second least vulnerable species to water stress after Juniperus, and yet it was by far the most vulnerable to the freeze-thaw treatment.}, interhash = {e8be48e158837f19efb0a09bde4319b1}, intrahash = {8e9cac619cbebdad92ebe2796e3f6380}, journal = {Plant Physiology}, keywords = {bibtex-import, citeulikeExport diameter, droughtbolism, freezebolism, snowgumpapermaybe}, pages = {605--613}, pdf = {\\biostore\desktop\$\u2531135\Desktop\references ideas and theory\papers\sperrysullivan\_92\_freezebolism\_drought\_trees.pdf}, posted-at = {2007-07-31 07:05:32}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse porous and conifer species}}, url = {http://www.plantphysiol.org/cgi/content/abstract/100/2/605}, volume = 100, year = 1992 }