Physiological and transplanting performance of Quercus ilex L. (holm oak) seedlings grown in nurseries with different winter conditions

Abstract

Resistance to drought and frost is a requisite for seedling survival and growth in Mediterranean continental areas. Environmental conditions in the nursery influence the functional characteristics of seedlings. We addressed if cultivation in nurseries that experience different winter conditions affected cold hardiness and other functional attributes relevant for transplanting performance of Quercus ilex (holm oak) seedlings. It was hypothesised that plants grown at cold-winter sites have higher stress resistance, vigour, and transplanting performance than the seedlings cultivated in mild-winter sites. We also studied if current root growth activity, determined as the number of white roots on the plug surface, can be used to predict frost hardiness. Seedlings from the same seed lot were cultivated at an inland and a coastal nursery, the former having colder winters than the latter. Cultural practices in both nurseries were similar. On seven dates from mid-summer 2000 to mid-spring 2001, frost damage was assessed by shoot mortality and electrolyte leakage after freezes to either −12 °C or −19 °C. Potential drought tolerance, root growth capacity, plant morphology, shoot nutrient and soluble sugar concentration were determined in late fall and in mid-winter. Seedlings were transplanted at an inland site in late fall and in mid-winter and their survival and growth was measured for 2 years. Coastal plants cold hardened latter in the fall and dehardened earlier in the spring than inland seedlings. In the fall and in early spring, coastal plants had greater frost damage and shoot mortality than inland seedlings at both −12 and −19 °C. In mid-winter, frost damage and shoot mortality after −12 °C did not differ between nurseries but was greater in coastal plants after −19 °C. Inland plants had lower osmotic potential either at full turgor or at the turgor loss point suggesting they were potentially more drought-tolerant. Inland seedlings were bigger, concentrated more shoot N and soluble sugars, and had higher specific leaf mass and root growth capacity than coastal seedlings. Current root growth activity had the same seasonal variation pattern at both locations and did not correlate with frost hardiness. Nursery location did not affect transplanting mortality. However, inland seedlings had greater growth than coastal seedlings when planted in mid-winter planting but not in late fall. This study demonstrates that differences in winter conditions in the nursery have a strong effect on the functional and transplanting performance of Q. ilex seedlings and that current root growth activity cannot be used as a predictor of the frost hardiness in this oak.