Seasonal variations in acidic pollutant inputs and their effects on the chemistry of stemflow, bark and epiphyte tissues in three oak* woodlands in N.W. Britain

Abstract

SUMMARYRainfall, throughfall and stemflow chemistry, bark chemistry and gaseous air pollutant levels were monitored for one year within three Quercus petraea (Mattuschka) Liebl. woodlands in north west Britain. Tissue chemistry of the epiphytic lichen Lobaria pulmonaria (L.) Hoffm, and the moss hothecium myosuroides Brid. were also studied at the sites in which they were abundant. The sites were found to difFer in the levels of acidic and nutrient inputs, bark chemistry and levels of gaseous pollutants, although the latter were low at all the sites. The epiphyte tissue chemistry responded to changes in stemflow chemistry across the season. At Borrowdale. Cumbria, where acid sensitive lichens have declined, stemflow was always of a low pH (3-5-4-5) and lou nutrient content. The tissues of /. myosuroides at this site had low concentrations of nutrient cations, but a high nitrogen content, possibly due to a high nitrate input in the rainfall. It is concluded that acid precipitation will affect epiphytes by reducing the bark's buffering capacity and increasing its acidity. The extent to which this occurs will depend on tree species, soil chemistry and the nature of the atmospheric inputs. This is discussed in the context of the concept of critical loads for acidifying deposition.

The deposition of atmospheric ammonia and its effects on plants

“…Cadle et al (1991) found for a range of species fumigated with nitric acid vapour, that stem and branches adsorbed 5-10 times more than the leaves when calculated on an area basis. Several workers have also shown that twigs and bark enrich throughfall to a greater extent than leaves (Schulze, 1989;Farmer et al, 1991). Van Breeman et al (1982) found that stemflow was enriched with ammonium to a greater extent than throughfall in an oak/birch woodland.…”

“…Potter et al (1991) found that nitrification of ammonia by leaf surface microflora played no role in nitrogen transformation in an American hardwood forest. Epiphytic macroflora can, however, impose problems for interpretation of stemflow nutrient changes (Farmer et al, 1991). Work on beech showed that algae probably played a significant role in nitrogen losses, judging from a '''N budget analysis.…”

Traffic exposure increases natural 15N and heavy metal concentrations in mosses

“…Most workers have tended to concentrate on species growing in grassland, for example Hylocomium splendens and Pleurozium schreberi (Ross, 1990), or on Sphagnum species from ombrotrophic mires (Press et al, 1986 ;Pitcairn et al, 1995). Epiphytic mosses, usually those on tree trunks, have also been used, for example Hypnum cupressiforme (Goodman & Roberts, 1971) and Isothecium myosuroides (Farmer et al, 1991). However, these groups of species are often absent from the urban environment, or are of limited value for this kind of work in towns and cities where a good deal of the pollution from traffic occurs (Goodman & Roberts, 1971 ;Ross, 1990 ;Tyler, 1990).…”

Manganese as a site factor for epiphytic lichens

“…In contrast to the element content of soil, there is no standard method for determining the availability of cations from bark. While in numerous studies, including HAUCK (2000) and HAUCK et al (2001b), the element content of bark is specified as the total content, extracts with SrCl 2 or BaCl 2 were used for cation measurements by FARMER et al (1991) and GOWARD & ARSENAULT (2000). However, these extractants are perhaps not appropiate for assessing the exchangeability of heavy metals from organic surfaces (BRANQUINHO et al 1997) physodes soredia, even before they start to grow.…”

“…In low-polluted areas, cation uptake and resulting physiological effects have been scarcely studied in lichens (HAUCK 2003), cation sources for lichens are the substrate, precipitation and particles from dry deposition (FARMER et al 1991, HAUCK 2000. ULOTH (1861) showed that the foliose lichens Evernia prunastri had higher concentration of Fe on sandstone than on birch bark.…”