![]() ![]() Drought-induced embolism occurs when low ψ causes the air contained in air filled cells to be sucked through the pits of water-filled xylem conduits, forming bubbles that block the conduit ( Zimmermann 1983). The mechanism by which drought and frosts cause xylem embolism is different ( Zimmermann 1983), but in both cases the amount of embolism is expected to increase with declining xylem water potential (ψ) ( Davis et al. However, while simple and fast, EL or fluorescence of photosystems do not inform on the capacity of individuals to remain alive after a stress event. 2009), while few studies report plant survival ( Hawkins et al. Most comparative studies on frost tolerance use foliage EL or decrease in fluorescence activity of photosystems to assess tissue damage ( Strand and Öquist 1988, Climent et al. These physiological responses reduce the productive capacity and hydration of plants, and might damage the plant and eventually cause their death ( McCulloh et al. Particularly, water transport and gas exchange are usually reduced due to frost-induced embolism and drought-induced stomatal closure ( Sperry and Sullivan 1992, Davis et al. Both stress factors affect important plant physiological processes ( Sakai and Larcher 1987, Mayr et al. This study demonstrates that freezing temperatures are a major environmental driver for pine distribution and suggests that interspecific differences in leaf frost sensitivity rather than vulnerability to freezing-induced embolism or SS explain pine juvenile frost survival.ĭrought and frosts are major drivers of plant evolution and distribution ( Woodward and Williams 1987, Pockman and Sperry 1997, Choat et al. uncinata and had a neutral effect on the rest of the species. Reduction in ψ pd decreased leaf frost damage in P. Freezing-induced PLC was very low and differences among species were not related to frost damage. and, to a lesser extent, Pinus pinaster Ait.) had the lowest frost survival and highest needle EL and SS values. In contrast, the pines inhabiting mild or cool winter locations (especially Pinus halepensis Mill. DC.) had the highest frost survival rates and lowest needle EL and soluble sugar (SS) concentration. Species experiencing cold winters in their range ( Pinus nigra J.F. We studied survival to a range of freezing temperatures in 2-year-old plants and assessed the percentage loss of hydraulic conductivity (PLC) due xylem embolism formation and foliage damage determined by needle electrolyte leakage (EL) after a single frost cycle to −15 ☌ and over a range of predawn water potential (ψ pd) values. We also evaluate if frost tolerance depends on plant water status. The objective of this study was to analyse if the distribution of six common pine species along latitudinal and altitudinal gradients in Europe is related to their interspecific differences in frost tolerance and to the physiological mechanisms underlying species-specific frost tolerance. ![]() Both stresses can cause xylem embolism and foliage damage. Drought and frosts are major determinants of plant functioning and distribution. ![]()
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