| Popis: |
Four nitrogen (N) levels, spanning those found naturally, were established in Calluna vulgaris grown in containers in an oceanic climate for 4 years on the southwest coast of Norway. Established N contents of the plants were 0.7, 0.8, 1.3 and 2.5% of dry weight. Experiments comprising 5000 plants were performed in the open and in growth chambers. In the open, dry matter accumulation and date of bud burst were recorded at the different N levels. Breaking of winter dormancy was studied under controlled conditions. In October/November, plants needed 1474 day-degrees for bud burst at the lowest N level, whereas at the highest level only 582 day-degrees were required. The natural start of growth in the field was on 14 April at the highest N level and on 26 April at the lowest. Freeze testing of the shoots (with the roots protected from frost) revealed that Calluna tolerates temperatures as low as −15 °C as late as the beginning of April. However, plants at the two medium N levels were most tolerant of frost. During the last winter of the experiments, nearly 50% of plants in the open died at the highest N level, whereas plants at the lower levels survived without damage. The effects of N are discussed in relation to the influence on physiological ageing of the plants, the change in nutrient balance of the plant tissue and the subsequent increase in susceptibility to biotic and abiotic stresses. |
