Effects of nitrogen addition on the stress sensitivity of Calluna vulgaris

Abstract

The effects of low levels of nitrogen addition (7n7 and 15n4 kg N ha −" yr −" ) on plant sensitivity to biotic and abiotic stress were studied at a lowland heath in the south of England that has received N treatments since 1989. Larval growth rates and adult weights of heather beetles were found to be significantly higher when insects were reared on plants that had received additional N, with implications for insect survival and reproductive success. Electrolyte leakage measurements failed to reveal any significant impact of N addition on plant sensitivity to frost episodes in early winter. In April, however, there was some evidence of slightly decreased frost hardiness in plants receiving additional N. Accelerated spring bud burst also suggested earlier physiological activity in N-treated plots. The rate of water loss from excised shoots of Calluna vulgaris (L.) Hull was significantly faster in plants receiving additional N, although no difference in plant water potential was measured in the field after a prolonged dry spell. Whilst experimental N addition had only a small effect on plant sensitivity to abiotic stress, the relationship between enhanced deposition and increased insect performance was clear, with the potential for substantially increased insect damage at deposition rates around the critical load contributing to the formation of gaps in the Calluna canopy.

The effect of nutrient supply and light intensity on tannins and mycorrhizal colonisation in Dutch heathland ecosystems

“…The increased dominance of grasses has been attributed to their higher growth rate potential than that of dwarf shrubs (Berendse and Elberse 1990). Furthermore, outbreaks of heather beetle in nitrogen-fertilised vegetation have also strongly accelerated the expansion of grasses (Heil and Diemont 1983;Bobbink and Heil 1993;Power et al 1998). Other factors (e.g.…”

“…Other factors (e.g. drought-and frost resistance of dwarf shrubs) can also be affected by changes in nitrogen deposition (Power et al 1998). …”

Potential Approaches to Developing Lichen-Based Critical Loads and Levels for Nitrogen, Sulfur and Metal-Containing Atmospheric Pollutants in North America

“…Measurements of plant characteristic demonstrated decreases in the root:shoot ratios in both C. vulgaris and Deschampsia flexuosa. Power et al (1998b) also found higher water losses from C. vulgaris plants from the nitrogen-treated vegetation, compared with the control situation, but no differences in water potential of the shoots. Hence the hypothesis that increased nitrogen deposition might lead to severe growth reduction or even local 'browning' and die-back of this species in cases of severe drought episodes is still mostly speculative.…”

“…The sensitivity decreased again two months later and no significant effects of the ammonium sulphate application upon frost hardiness were measured at that time. All these studies used high levels of nitrogen deposition; however, the only study of the effects of low levels of nitrogen addition (7.7 & 15.4 kg N ha -1 yr -1 ) on frost sensitivity of C. vulgaris showed no significant effects after seven years of treatment (Power et al, 1998b). Hence, the significance of increased frost sensitivity at ambient nitrogen loads is very uncertain and application of ammonium nitrate may even reduce frost sensitivity.…”

“…After field additions of ammonium sulphate in a roofed heath experiment, total number or biomass of the 1st stage larvae of the beetle was not affected by the treatments, but the development of subsequent larval stages was significantly accelerated ( Van der Eerden et al, 1990). Larval growth rates and adult weight of heather beetles were found to be significantly higher when these insects were reared on C. vulgaris plants, which were collected in the British lowland heath experiment, after seven years of relatively low nitrogen addition (Power et al, 1998b).…”