Effect of nitrogen supply on frost hardiness in Calluna vulgaris (L.) Hull.

Abstract

SUMMARYFrost hardiness in Calluna vulgaris (L.) Hull, which had received ammonium nitrate applications in the field for 30 months, was assessed using scores of visible injury and measurements of the rate of total electrolyte leakage from excised shoots following controlled freezing treatments in the laboratory. There was good overall correlation between the two methods (Spearman correlation coefficient 0-77), but leakage measurements were more sensitive than injury scores to the efFects of nitrogen. Visible injury was not significantly altered by nitrogen supply (Kruskal-Wallis non-parametric test). Ion leakage was analyzed in different ways, using either calculations of the first-order rate coefficients or expressions of relative conductivity. These analyses produced similar results with respect to the effect of frost and nitrogen. Shoots of nitrogen-fertilized (40, 80 and 120 kg ha"^ yr'^) C. vulgaris sampled in October 1991 showed significantly {P < 0-05) less leakage after overnight frosts of -15 and -20 °C than did the water-treated controls. In October the temperature which killed 50% of the shoots (LT,,,,), derived from the leakage data, was raised by at least 4 °C by the highest nitrogen treatments compared with the control plants. Frost treatments to pot-grown C. vulgaris in November produced similar visible injury to attached and excised shoots from the same plants, both being significantly less damaged by a -18 °C frost after a 7-month exposure to an NaNOg mist solution (1-0 mM, pH 4-5) than were water-misted controls. Ammonium-mist treatments also marginally reduced frost injury, but the effects were not statistically significant. These results demonstrate that frost hardiness of C. vulgaris in the field can be assessed rapidly and accurately in the laboratory by analysis of electrolyte leakage from excised shoots.

Differential responses of UK upland plants to nitrogen deposition

“…The much greater above-ground response demonstrated by the dwarf ericoid shrubs may be beneficial when nutrients and water are not limiting and competition is for light with graminoids such as N. stricta and E. vaginatum. Aerts et al (1990) showed that C. vulgaris can compete successfully with invasive grass species such as M. caerulea at high N deposition but only if the canopy is undisturbed by factors such as severe frosts (Caporn et al, 1994), grazing (Hartley, 1997) or heather beetle attacks (Brunsting & Heil, 1985). The balance between V. vitis-idaea and E. cinerea and the two graminoids in the present study may be similar.…”

“…5% will have a deposition 30 kg N ha −" yr −" (derived from CLAG, 1997). Semi-natural plant communities in these upland areas are adapted to small atmospheric N inputs and some species have been shown to be sensitive to increased atmospheric inputs of inorganic N (Caporn et al, 1994(Caporn et al, , 1995. Reduced growth at N concentrations of 0n01 mM was reported for Sphagnum cuspidatum (Press et al, 1986).…”

The effect of increased deposition of atmospheric nitrogen on Calluna vulgaris in upland Britain

“…Previous publications have described either the early results of this experiment (Lee et al, 1992 ;Caporn et al, 1995) or specific aspects relating to frost tolerance (Caporn et al, 1994b) and mycorrhizas (Caporn et al, 1995). This paper presents the effects on growth and winter injury after 8 yr of continuous experimentation and observation.…”

“…Increases in the long-term rate of nitrogen supply are therefore likely to lead to changes in the structure of the community, including the loss of more sensitive species (Press et al, 1986 ;Pitcairn & Fowler, 1995) and a shift in the structure of the vegetation towards more competitive species (Heil & Diemont, 1983 ;Bobbink, 1991). The increased availability of nitrogen to plants can alter the balance of shoot and root growth (Marschner, 1986), disturb the normal seasonal phenology (Caporn et al, 1994b), and lead to increased levels of tissue nitrogen (Pitcairn & Fowler, 1995). There is some evidence that these changes could in turn increase the susceptibility of the vegetation to a range of environmental stresses such as frost, drought and herbivory (Green et al, 1997).…”

Effects of excess nitrogen on frost hardiness and freezing injury of above‐ground tissue in young oaks (Quercus petraea and Q. robur)

“…This method has been widely adopted to test the frost hardiness of various parts of trees such as stem sections (van den Driessche, 1976), twigs (Alexander et al, 1984) and needles (Burr et al, 1990). More recently, Murray et al (1989) developed a method based on the rate of electrolyte leakage, which has been used successfully to quantify the freezing injury to woody shoots in, for example, Calluna vulgaris (Caporn et al, 1994), Quercus petraea (Deans et al, 1995) and Picea abies (Sheppard et al, 1995). In our investigation we compared both methods with a visual assessment of the freezing damage, which was performed with bark and buds after incubation with a solution containing 2,3,5-triphenyltetrazolium chloride (TTC).…”