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

Abstract

 Regular (monthly) additions of NH% NO $ (4-12 g N m −# yr −" ) were made over a period of 8 yr to areas of moorland in North Wales dominated by the ericaceous shrub Calluna vulgaris. Results from the early stages of the experiment have shown marked and dose-related increases in shoot extension and canopy height in response to the nitrogen treatments, with significantly higher shoot nitrogen contents. The nitrogen-related stimulation in the growth of the C. vulgaris canopy over this period has resulted in large accumulations of litter on the high-nitrogen-treated plots (6n6 kg m −# in plots treated with 12 g N m −# yr −" , compared with 3n8 kg m −# for the water controls). Litter nitrogen concentrations were also significantly increased at the higher rates of nitrogen addition, leading to a doubling of the total return of nitrogen to the litter layer over the experimental period. These changes in vegetation structure were associated with large reductions in the abundance of the bryophyte and lichen species normally present under the untreated canopy. Results since 1994, however, show little increase in shoot extension in response to the nitrogen treatments, with no clear dose response to increasing levels of addition. These findings are associated with a dose-related increase in the susceptibility of the nitrogentreated areas of the C. vulgaris canopy to late winter injury, characterized as browning of the shoot tips in early to late spring. These results indicate that deleterious effects are now accumulating as a result of the long-term addition of nitrogen to these moorland plots.

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

“…In this case, the available carbon is invested in growth rather than in defence. It is well established that nitrogen addition increases nitrogen concentrations in heather, C. vulgaris (Berdowski and Siepel 1988;Duncan et al 1994;Hartley et al 1995;Carrol et al 1999;Gordon et al 1999) and other ericaceous plants (Mallik 1996;Prescott et al 1993;Nordin et al 1998). However, the expected decrease in total phenolics or condensed tannin levels due to solely nitrogen additions has not yet been empirically shown either in the greenhouse or in the field (Iason and Hester 1993;Hartley et al 1995;Kerslake et al 1998;Bradley et al 2000;Alonso et al 2001;Hansen et al 2006).…”

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

“…In the earlier years, both bryophytes and lichens had disappeared from below the C. vulgaris canopy in all nitrogen addition treatments, although Vaccinium myrtillus maintained its cover (Carroll et al, 1999). It is not certain, however, whether this was a response to direct effects of nitrogen addition or through changes in C. vulgaris canopy architecture and increased litter production resulting in reduced light penetration.…”

“…The following three years of the study, however, showed a much reduced effect of the treatment on shoot extension, and no clear dose response to increasing nitrogen inputs. The 1996 data in particular showed no effect of nitrogen on shoot extension at all (Carroll et al, 1999). One interpretation of the C. vulgaris growth responses in this experiment is that addition of N has accelerated the natural C. vulgaris cycle, with earlier ageing and opening of the canopy in the highest treatment plots.…”

“…However, field surveys in 1996 and 1998 clearly showed large increases in 'winter browning' of heather shoots, most notably in the 80 and 120 kg N ha -1 yr -1 treatments (Fig. 4.1) (Carroll et al, 1999;Lee et al, 2000). This damage mechanism may be the result of low temperature desiccation, rather than frost damage.…”

“…This site has been estimated to receive a current atmospheric nitrogen deposition of approximately 20 kg N ha -1 yr -1 , although more recent assessments suggest that the deposition is somewhat higher. Additions of nitrogen in the form of ammonium nitrate at doses of 0, 40, 80 and 120 kg N ha -1 yr -1 have been applied since 1989 at monthly intervals and continue to date (Lee and Caporn, 1998;Carroll et al, 1999). The period from 1989 to 1993 was characterized by apparently beneficial effects of nitrogen on C. vulgaris in terms of improvements in shoot growth, nitrogen concentration and flowering, with no indication that the dose applied exceeded the capacity of the plants for uptake and subsequent growth.…”