The physiological responses of oak seedlings to warm storage

The effects of warm storage (15 °C) on the physiological responses and subsequent field performance of 2-year-old oak (Quercus robur L.) seedlings that had been cold (1–2 °C) stored until May were assessed. Shoot xylem pressure potential, shoot water content, shoot tip dry mass, root electrolyte leakage, and root growth potential were evaluated at regular intervals during the 21-day warm storage period. The date of lifting to cold storage had little effect on the physiological responses to warm storage. Root electrolyte leakage increased after 7 days of storage, despite the fact that root growth potential and survival were unaffected. Values then increased further before decreasing again by the end of the 21-day storage period to values similar to those recorded after 0 or 7 days of storage. Storage for up to 21 days greatly reduced root growth potential and shoot quality after planting in the field. The shoot xylem pressure potential of seedlings declined during the early stage of warm storage, but then increased to values similar to those recorded after cold storage. Shoot water content increased during the early storage period, then declined slightly, but values were higher after 21 days of storage than at the time of placement in warm storage. While most physiological responses fluctuated in a consistent manner, these changes were not necessarily predictable. Root growth potential was a good indicator of plant field performance potential, but the other physiological parameters were less useful to this end.