Response of phosphomonoesterase activity in the lichen Cladonia portentosa to nitrogen and phosphorus enrichment in a field manipulation experiment.

*Effects of nitrogen (N) enrichment on the heathland lichen Cladonia portentosa were quantified to test the hypothesis that modified N : phosphorus (P) relationships observed in this species in N-polluted natural environments are a direct effect of increased N deposition, and to evaluate potential confounding effects of N form and P availability. *Cladonia portentosa was harvested from experimental plots in lichen-rich peatland vegetation (background total N deposition of 8 kg N ha(-1) yr(-1)) treated for 4 yr with additional wet N deposition at 0, 8, 24 and 56 kg N ha(-1) yr(-1) as either NH(4)(+) or NO(3)(-), and with or without P added at either 0.6 or 4 kg P ha(-1) yr(-1). *Nitrogen enrichment increased thallus N concentration, N : P mass ratio and phosphomonoesterase (PME) activity by factors of up to 1.3, 1.4 and 1.7, respectively, effects being independent of N form. Phosphomonoesterase activity was tightly related to thallus N : P ratio with additions of P at 4 kg ha(-1) yr(-1) depressing PME activity by a factor of 0.4. *Nitrogen enrichment induces P-limitation in C. portentosa with attendant changes in chemical and physiological characteristics that could be used as sensitive biomarkers with which to detect low levels of N pollution.

Effects of nitrogen enrichment on phosphatase activity and nitrogen : phosphorus relationships in Cladonia portentosa.

*Relationships between nitrogen deposition in the UK and phosphomonoesterase (PME) activity and nitrogen (N) and phosphorus (P) concentrations in Cladonia portentosa were quantified to understand factors limiting lichen growth and to further develop biomarkers for N pollution. *Lichen was collected from sites differing either in rates of wet N (NH(4)(+) + NO(3)(-)) deposition or in annual mean N concentration in rainfall based on both measured and modelled data sets. The PME activity, and total N and P concentrations were measured in specific horizontal strata in lichen mats and PME activity in the thallus was located using an enzyme-labelled fluorescent phosphatase substrate. *With an increase in modelled N deposition from 4.1 to 32.8 kg N ha(-1) yr(-1), PME activity, thallus N and N : P ratio increased by factors of 2.3, 1.4 and 1.8, respectively. Correlations with modelled data were generally stronger than with measured data and those with N deposition were stronger than those with N concentration in rainfall. The PME activity was located solely in the lichen fungus in outer regions of the thallus. *Nitrogen enrichment changes lichen N : P ratios from values typical of N limitation (for example, 10) to those indicative of P limitation (for example, 26) driving upregulation of PME activity.

Growth and nitrogen relations in the mat-forming lichens Stereocaulon paschale and Cladonia stellaris.

BACKGROUND AND AIMS: Mat-forming lichens in the genera Stereocaulon and Cladonia have ecosystem-level effects in northern boreal forests. Yet the factors affecting the productivity of mat-forming lichens are not known. The aim of the presented work was to investigate whether mat-forming lichens adapted to low N availability employ N-conserving mechanisms similar to those of vascular plants in nutrient-poor ecosystems. Specifically, the following questions were asked: (a) Do lichens translocate N from basal areas to apical growth areas? (b) Are the quantities of N translocated of ecological significance. (c) Is lichen growth dependent on tissue N concentration [N]. METHODS: Two different, but complementary, field experiments were conducted using the mat-forming N2-fixing Stereocaulon paschale and non-fixing Cladonia stellaris as model species. First, N translocation was investigated by feeding lichens with Na(15)NO3 either directly to the apex (theoretical sink) or to the basal part (theoretical source) and observing the redistribution of (15)N after a growth period. Secondly, growth and variation in [N] in thalli of different lengths was measured after a growth period. KEY RESULTS: (15)N fed to lower parts of lichen was translocated towards the growing top, but not vice versa, indicating physiologically dependent translocation that follows a sink-source relationship. In the growth experiment where thalli were cut to different lengths, the significant decrease in [N] in apices of short vs. longer thalli after a growth period is consistent with internal relocation as an ecologically important source of N. CONCLUSIONS: The presented results demonstrate that internal recycling of N occurs in both species investigated and may be ecologically important in these mat-forming lichens under field conditions. The higher nitrogen use efficiency and relative growth rate in C. stellaris in comparison with S. paschale probably enable C. stellaris to dominate the ground cover vegetation in dry boreal coniferous forests under undisturbed conditions.

Translocation of 15N indicates nitrogen recycling in the mat-forming lichen Cladonia portentosa.

Nitrogen translocation was measured in Cladonia portentosa during 2 yr growth in Scottish heathland. Translocation was predicted to occur if N is resorbed from senescent basal tissue and recycled within the thallus. (15)N was introduced into either the lower (TU thalli) or upper (TD thalli) 25 mm of 50-mm-long thalli as (15)N-NH(4) (+), (15)N-NO(3) (-) or (15)N-glycine. Labelled thalli were placed within intact lichen cushions, either upright (TU) or inverted (TD). Vertical distribution of label was quantified immediately following labelling and after 1 and 2 yr. Independently of the form of introduced label, (15)N migrated upwards in TU thalli, with new growth being a strong sink. Sink regions for (15)N during year 1 (including new growth) became sources of (15)N translocated to new growth in year 2. Upward migration into inverted bases was minimal in TD thalli, but was again marked in new growth that developed from inverted apices. Relocation of N to regions of growth could facilitate internal N recycling, a process postulated to explain the ecological success of mat-forming lichens.

Regional variation in the chemical composition of winter snow pack and terricolous lichens in relation to sources of acid emissions in the Usa river basin, northeast European Russia.

The chemical composition of snow and terricolous lichens was determined along transects through the Subarctic towns of Vorkuta (130 km west-east), Inta (240 km south-north) and Usinsk (140 km, southwest-northeast) in the Usa river basin, northeast European Russia. Evidence of pollution gradients was found on two spatial scales. First, on the Inta transect, northward decreases in concentrations of N in the lichen Cladonia stellaris (from 0.57 mmol N g(-1) at 90 km south to 0.43 mmol N g(-1) at 130 km north of Inta) and winter deposition of non-sea salt sulphate (from 29.3 to 12.8 mol ha(-1) at 90 km south and 110 km north of Inta, respectively) were attributed to long range transport of N and S from lower latitudes. Second, increased ionic content (SO42-, Ca2+, K+) and pH of snow, and modified N concentration and the concentration ratios K+:Mg2+ and K+: (Mg2++Ca2+) in lichens (Cladonia arbuscula and Flavocetraria cucullata) within ca. 25-40 km of Vorkuta and Inta were largely attributed to local deposition of alkaline coal ash. Total sulphate concentrations in snow varied from ca. 5 micromol l(-1) at remote sites to ca. 19 micromol l(-1) near Vorkuta. Nitrate concentration in snow (typically ca. 9 micromol l(-1)) did not vary with proximity to perceived pollution sources.

Anthropogenic metal enrichment of snow and soil in north-eastern European Russia.

Trace metal composition of winter snowpack, snow-melt filter residues and top-soil samples were determined along three transects through industrial towns in the Usa basin, North-East Russia: Inta, Usinsk and Vorkuta. Snow was analysed for Ag, Al, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr and Zn using ICP-MS (Ca and K by F-AAS for Vorkuta only), pH and acidity/alkalinity. Filter residues were analysed for: Al, Ba, Ca, Cd, Cu, K, Mg, Mn, Ni, Pb, Sr and Zn using F-AAS and GF-AAS; top-soil samples were analysed for Ba, Cu, Mg, Mn, Na, Ni, Pb, Sr, Zn using F-AAS. Results indicate elevated concentrations of elements associated with alkaline combustion ash around the coal mining towns of Vorkuta and Inta. There is little evidence of deposition around the gas and oil town of Usinsk. Atmospheric deposition in the vicinity of Vorkuta, and to a lesser extent Inta, added significantly to the soil contaminant loading as a result of ash fallout. Acid deposition was associated with pristine areas whereas alkaline combustion ash near to emission sources more than compensated for the acidity caused by SO2.

Relationships between atmospheric nitrogen inputs and the vertical nitrogen and phosphorus concentration gradients in the lichen Cladonia portentosa.

The relationship between precipitation chemistry and the concentrations of nitrogen ([N]) and phosphorus ([P]) in the cushion-forming lichen Cladonia portentosa (Dufour) Coem. (=C. impexa (Harm)) was investigated. Samples of C. portentosa were collected from heathlands and upland moorlands close to 31 rural sampling stations in the UK Acid Deposition Monitoring Network, which provides data on wet deposition and NO2 concentrations in air. The [N] and [P] were measured in the top 5 mm of lichen thalli (thallus apices) and also in a horizontal stratum between 40-50 mm from the apices (thallus base). The [N] (per unit dry mass) was 0·08-1·82% and [P] was 0·04-0·17%, depending on collection site and lichen fraction analysed. Concentrations of both elements were c. 2-5 times greater in the apices than in the basal strata, and [N] and [P] values in each stratum were strongly positively correlated. Lichen [N] was positively correlated with N deposition: this relationship was stronger when using [N] values for thallus bases than for the apices. By contrast, thallus [N] was poorly correlated with [N] values in precipitation. When [NO2 ] in air was included together with NO3 - deposition in a linear regression model explaining thallus base N, the model fit was significantly improved, whereas modelled values of NH3 deposition rate for the heathland sites did not correlate with lichen [N]. It is suggested that the proportionately greater enrichment of [N] in the thallus base might reflect a perturbation of internal recycling of thallus N at polluted sites. Thallus [P] was generally weakly linked to wet N deposition but positively correlated with [NO2 ] in air. It is not known whether the trend for increasing thallus [P] values indicates decreasing lichen growth rate and reduced growth dilution of P in polluted areas, or is due to regional variation in P deposition rate.

Cation ratios in Cladonia portentosa as indices of precipitation acidity in the British Isles.

The relationship between rainfall chemistry and the concentrations of potassium, calcium and magnesium in the apices (top 5 mm) of the cushion-forming; lichen Cladonia portentosa (Dufour) Coem was investigated. Lichen samples, together with underlying topsoil, were collected from heathlands in close proximity to rain gauges in the UK Acid Deposition Monitoring Network, located in rural areas of the British Isles, which provide wet deposition data based on weekly bulk samples. The ratios K(+) : Mg(2+) and extracellular Mg(2+) : intracellular Mg(2+) in the lichen apices were strongly correlated with H(+) concentration in precipitation. It is suggested that shifts in these ratios occur owing to enhanced displacement of extracellular Mg(2+) by elevated H(+) concentration in acid rain. By contrast, there was no indication of any relationship between total acid deposition and lichen chemistry. The concentration of Mg(2+) in the lichen was weakly correlated with that in soil, whereas lichen Ca(2+) content was not correlated with either precipitation or soil chemistry. It is concluded that these ratios describing changes in lichen Mg(2+) content provide good biomarkers for wet-deposited acidity.

Effects of simulated acid rain on nitrogenase activity (acetylene reduction) in the lichen Stereocaulon paschale (L.) Hoffm., with special reference to nutritional aspects.

The effects of SAR (simulated add rain using H2 SO4 and HNO3 singly and combined) on ARA (acetylene reduction activity), and concentrations of N, K4 , Mg2+ and Ca2- was investigated in Sterecaulon paschale (L.) Hoffm. ARA was significantly decreased after 4 months of SAR at pH 3.0. One year after spraying treatments had ceased, lichens treated at pH 3.0. showed no clear signs of recovery of ARA. After 5 y of acidification. ARA in lichens sprayed with combined H2 SO4 and HNO3 at pH 2.9. was comparable to that observed after 4 months of pH 3.0.enhanced rain, i.e. close to zero. SAR at pH 4.0. had no marked effect on nitrogenase activity after 4 months' exposure, but ARA was significantly decreased after 5 y-of pH 4.1. (H2 SO4 ) treatment. There were no clear relationships between the inhibitory effects of acid additions and alterations in nutritional status in the lichen caused by SAR. Furthermore, no correlation between thallus N concentration and nitrogenase activity was observed.

Lichen-forming fungi: potential sources of novel metabolites.

The challenge for today's pharmaceutical industry lies in the discovery and development of new, pharmacologically active molecules. Metabolites produced by microorganisms, and fungi in particular, are a resource for which the therapeutic potential has been recognized, but one that remains largely unexplored and unexploited. Approximately 20% of all known fungal species are obligate symbionts in lichens; this major group of fungi has been long neglected by mycologists, and overlooked by industry.