Temporal changes in tissue water relations of seedlings of Quercusacutissima, Q. alba, and Q. stellata subjected to chronic water stress

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Abstract
In a greenhouse experiment, seedlings of Quercusacutissima, Quercusalba, and Quercusstellata were subjected to several lengthy drying cycles or were kept well watered. Three times during the 94-day experiment, samples were obtained for pressure–volume analysis of leaves so that tissue water relations responses to long-term water stress could be assessed. There was a general temporal decline in osmotic potential at full turgor (ψπ0) and at the turgor loss point (ψπp) for well-watered seedlings of all species. In water-stressed seedlings, ψπ0 declined from the first (pre-stress) to second sample dates, but then showed a subsequent increase from the second to third sample dates. Despite this increase in ψπ0, ψπp declined in the latter part of the experiment in water-stressed seedlings because of substantial increases in tissue elasticity. The late-period increase in ψπ0 in water-stressed plants was attributable to declines in solute levels and not to increased osmotic volume, as the latter showed a distinct decrease over the experiment. Although slight reductions in ψπp for water-stressed plants compared with values for well-watered plants were noted for Q. acutissima and Q. alba at the second sample date of the experiment, these differences were not significant. By the experiment's end, ψπp values for plants of both treatments were similar for all species. These results indicate that there is a limit to the capacity for solute accumulation under chronic water stress in Quercus, but that compensatory responses of tissue elastic properties may offset this influence.
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