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- Title
Effects of excess nitrogen on frost hardiness and freezing injury of above-ground tissue in young oaks (<em>Quercus petraea</em> and <em>Q. robur</em>.
- Authors
Thomas, F. M.; Ahlers, U.
- Abstract
The effects of excess nitrogen (N) on the frost hardiness and freezing injury of bark and buds were tested in 2-yr-old sessile oaks (<em>Quercus petraea</em>) and pedunculate oaks (<em>Q. robur</em>) that had been grown outdoors in sand culture with normal or luxurious N supply during the growing season. Some trees from both N treatments were subjected to drought stress in summer, whereas others were adequately watered. Between January and March, whole plants were exposed to artificial freezing treatments at - 25°C of different durations (10 d, 21 d, or two periods of 4 d interrupted by an 8 d frost-free period, referred to as a freeze thaw cycle). The frost hardiness and freezing injury of the bark were determined by two different versions of the electrolyte leakage method (calculation of an index of injury, <em>I</em>-25, from the relative conductivity after a fixed time; and measurement of the electrolyte leakage rate). In addition, the vitality of bark and buds was assessed visually with the 2,3,5-triphenyltetrazolium chloride (TTC) method. In comparison with the control, the oaks that had been luxuriously supplied with N exhibited distinctly higher N concentrations and lower C : N ratios in their leaves and bark, higher relative shout increments, delayed leaf discoloration in autumn, and earlier budbreak in spring. Oaks kept outdoors during the winter were frost-hardy from December until the end of February without showing differences between species or N treatments. In comparison with the pedunculate oak, the sessile oak was more susceptible to freezing injury induced by prolonged artificial freezing or by the freeze-thaw cycle. Increased freezing injury in trees with high N supply was detected only by the TTC test of tile bark of sessile oaks subjected to the freeze-thaw cycle. In all oaks, except for the pedunculate oaks grown with normal N, the freeze-thaw cycle resulted in significantly lower frost hardiness, as indicated by increased <em>I</em>-25 values. This treatment also led to increased freezing damage of bark and buds, as revealed by the TTC test. In drought-stressed oaks, the electrolyte leakage rate was significantly elevated after the freeze-thaw cycle. It is concluded that, in the sessile and pedunculate oaks, the water supply before frost stress and the course of the temperature in winter have a greater effect on frost hardiness and freezing damage than excess N.
- Subjects
DURMAST oak; ENGLISH oak; BUDWOOD; BUDDING (Plant propagation); FALL foliage; ELECTROLYTES
- Publication
New Phytologist, 1999, Vol 144, Issue 1, p73
- ISSN
0028-646X
- Publication type
Article
- DOI
10.1046/j.1469-8137.1999.00501.x