Nitrophytic Lichen Research Articles

Lichens as a useful mapping tool?—an approach to assess atmospheric N loads in Germany by total N content and stable isotope signature

To assess whether nitrogen (N) content and δ(15)N ratios in nitrophytic lichen species (Xanthoria parietina (L.) Th. Fr. (1860) and Physcia spp. (Schreb.) Michaux (1803)) reflect the quantity and quality of atmospheric N loads, 348 lichen samples from 174 sampling grid cells were investigated in the western part of Germany. The analysed lichen N content ranged between 0.98 and 4.28% and δ(15)N ratios between -15.2 and -1.3 ‰. Based on the N concentrations and the δ(15)N ratios of lichens, different landscape categories and coupled N deposition rates could be inferred for different regions of Germany. By analysing environmental variables like altitude, ammonia emission density, livestock unit and different defined deposition types, a direct relationship was found between lichen chemistry and N compounds produced from agricultural activity. The results support the development of a monitoring method which could be used nationally or even internationally to support current N deposition measurements, by providing reliable information on the quantity and quality of N deposition in high N environments.

Sensitivity of Lichens to Diesel Exhaust under Laboratory Conditions

Lichen vegetation reacts very sensitively to a variety of air pollutants including increased nitrogen concentrations as well as to traffic exhaust in general, which makes lichens reliable monitoring organisms for atmospheric pollution. Recent environmental studies have shown that decreasing abundance of acidophytic lichen species and the increase of nitrophytic lichens can be explained by elevated levels of atmospheric nitric-compounds adsorbed onto nanoparticles. One major source of these atmospheric compounds amongst a wider pollution inventory is diesel exhaust—a mixture of gases and particle matter. This study aimed to shed light on the impact of diesel exhaust on the viability of six differently sensitive lichen species. Diesel exhaust particle concentrations in the laboratory experiments resembled those at a local highway during rush hour. By incubation in a closed stainless steel chamber we could exclude influences from other pollutants than diesel exhaust providing explicit data about the effects of diesel exhaust on lichens. The investigations revealed effects on the photosynthesis of the lichen photobionts and hence the lichen vitality. The conclusions of this study are that 1) the photobiont is affected stronger as the mycobiont and 2) older parts of the lichen are damaged first. Another remarkable result of this study is that 3) these lichens are regenerating to some extent during incubation-free periods—unless the organism is not damaged too much to restore photosynthetic activity. To our knowledge this is the first study evaluating the impact of diesel exhaust on lichens under laboratory conditions separate from other interfering pollutants.

Forest edge-interior differentiation in the epiphytic lichen diversity of the forest steppe in the Khangai Mountains, Mongolia

The effects of traditional land use by mobile livestock keepers on biodiversity in forest steppe ecotones are insufficiently studied. Epiphytes are an important part of forest plant diversity. Here we analyze differences in the diversity and composition of the epiphytic lichen vegetation between the edge and the interior of Siberian larch forests in the Khangai Mountains, western Mongolia, which are highly subdivided into patches. We asked whether the epiphytic lichen vegetation at the forest edge differs significantly from that in the interior, whether the edge is inhabited by more nitrophilous species than the interior and whether the density of nomad camps around the forest affects epiphytic lichen diversity. Cover percentages of epiphytic lichen species were recorded from 20 trees per plot on 6 plots in the interior and 6 plots at the edge of Larix sibirica forests. The position of nomad summer camps was surveyed using Global Positioning System. Data were analyzed with pairwise significance tests, analysis of similarities, nonmetric multidimensional scaling and canonical correspondence analysis. The composition of the epiphytic lichen vegetation clearly differed between the two habitats, with more species being more frequent at the edge than in the interior. However, there was no difference in species richness (α-diversity). The epiphyte vegetation at the edge was more uniform and characterized by lower variation of tree-level α-diversity and lower β-diversity than in the interior. At the edge, only nitrophytic lichens were dominant, whereas in the interior, nitrophytes and acidophytes were among the dominant species. This pattern is probably attributable to the spatial heterogeneity of the intensity of forest grazing and was shown to be influenced by the density of nomad summer camps in the vicinity of the forests. Tree-level α-diversity increased with stem diameter, but high-diameter trees were rare. The results suggest that the present level of forest patchiness and the effect of forest grazing increases the diversity of epiphytic lichens on the landscape level, while logging of high-diameter trees reduces lichen diversity.

Source attribution of agriculture-related deposition by using total nitrogen and δ15N in epiphytic lichen tissue, bark and deposition water samples in Germany

Compared with physico-chemical deposition measurement methods, lichens are able to identify the long-term overall effects of high N pollution concentrations in the air. In addition, the natural abundances of the stable isotope of N, 15N, are being widely used in research on N cycling in ecosystems. They can also be used as instruments for source attribution. In this study, epiphytic lichens were tested to determine whether their respective N content and δ15N ratios can be used to estimate N deposition rates and to locate various sources of N compounds. Epiphytic lichen and bark samples were collected from around various deposition measurement field stations at different sites in the western part of Germany. The N content of epiphytic lichens reflects the species-specific, agriculture-related circumstances of N deposition at various sites in Germany. At the same time, δ15N signatures of the different investigated epiphytic lichen species and bark samples are highly depleted in 15N under high ammonium deposition. The different surface types of lichens and barks exhibit different concentrations of N and δ15N ratios, despite being exposed to similar N deposition rates. The verification of highly negative δ15N ratios at sites with local and regional emitters shows that source attribution is possible by comparing different δ15N signatures in areas with a wide range of different N deposition types and the corresponding differences in δ15N among various source N pools. Especially nitrophytic lichens can support the on-site instrumentation measuring N deposition by qualification and quantification.

Monitoring H 2S air pollution caused by the industrial exploitation of geothermal energy: The pitfall of using lichens as bioindicators

This study showed that NH 3 emitted from geothermal power plants affects the surrounding epiphytic lichen vegetation and diversity, confounding the interpretation of lichen diversity counts in terms of air pollution by H 2S. The presence of nitrophytic lichen species around geothermal installations, determined by NH 3, caused relatively high diversity values that were not related with the levels of air pollution by H 2S. It is recommended that in the presence of NH 3 emission, nitrophytic species are excluded from the calculation of lichen diversity values.

Effects of reduced nitrogen compounds on epiphytic lichen communities in Mediterranean Italy

The effects of reduced nitrogen compounds on epiphytic lichen vegetation have been largely investigated in northern Europe. This paper reports for the first time results of a study carried out on pine trees in the Mediterranean basin. Contrary to the usual acidophytic lichen colonization of pine bark, in this case a nitrophytic lichen vegetation was found, suggesting that the study area is characterized by a diffuse eutrophication. Tree circumference, distance from the stock farms, bark pH and bark electrical conductivity emerged as the main factors influencing the distribution and abundance of epiphytic lichens in the study area. Both Hyperphyscia adglutinata and Xanthoria parietina were suitable local indicator species of high pine bark pH values. However, while X. parietina indicated high nitrogen dust pollution, H. adglutinata occurred also where there was an additional increase in bark pH caused by the release of high amounts of ammonia. The increased nitrogen availability caused by ammonium apparently had no effect on the occurrence of nitrophytes.

Lichens on branches of Siberian fir (Abies sibirica Ledeb.) as indicators of atmospheric pollution in forests

The abundance distribution of different ecological groups of lichens depending on bark pH has been studied on 1- to 24-year shoots of Siberian fir in the mountains of southern Siberia. Along with acidophytic lichens commonly found on the Siberian fir (Usnea sp., Bryoria sp., etc.), its young shoots are also colonized by nitrophytic species (Physcia tenella, Melanelia exasperatula, etc.), which is evidence for the increasing pH of shoot bark. The proportion of thalli of nitrophytic lichen species shows a significant positive correlation with the pH of the upper (dusted) bark layer and is greater in the Eastern Sayan (at bark pH averaging 5.4) than in the Western Sayan (pH 4.7). The trends revealed in this study may be used for indication of pollution and ecological monitoring of forest ecosystems.

Atmospheric deposition inputs and effects on lichen chemistry and indicator species in the Columbia River Gorge, USA

Topographic and meteorological conditions make the Columbia River Gorge (CRG) an ‘exhaust pipe’ for air pollutants generated by the Portland-Vancouver metropolis and Columbia Basin. We sampled fog, bulk precipitation, throughfall, airborne particulates, lichen thalli, and nitrophytic lichen distribution. Throughfall N and S deposition were high, 11.5–25.4 and 3.4–6.7 kg ha −1 over 4.5 months at all 9 and 4/9 sites, respectively. Deposition and lichen thallus N were highest at eastern- and western-most sites, implicating both agricultural and urban sources. Fog and precipitation pH were frequently as low as 3.7–5.0. Peak NO x, NH 3, and SO 2 concentrations in the eastern CRG were low, suggesting enhanced N and S inputs were largely from particulate deposition. Lichens indicating nitrogen-enriched environments were abundant and lichen N and S concentrations were 2× higher in the CRG than surrounding national forests. The atmospheric deposition levels detected likely threaten Gorge ecosystems and cultural resources.

Nitrogen uptake in relation to excess supply and its effects on the lichens Evernia prunastri (L.) Ach and Xanthoria parietina (L.) Th. Fr.

The aim of this study was to compare the physiological responses to increased nitrogen (N) supply between the nitrophytic lichen Xanthoria parietina (L.) Th. Fr. and the acidophytic lichen Evernia prunastri (L.) Ach. The two lichens were exposed to a weekly dosage of 0.05, 0.1, 0.2, 0.6 or 2.4 g N m(-2) for 2 months, administered as NH(4)NO(3) dissolved in artificial rainwater (1 l m(-2)). After the treatments, in vivo chlorophyll a fluorescence was determined to assess vitality; concentrations of total N, ammonium, nitrate and dominant amino acids, including glutamate, glutamine and arginine, were quantified in order to follow changes in N status; and the polyols ribitol, arabitol and mannitol were quantified to follow changes in the lichens' carbon (C) status. The uptake of N was quantified by labelling the fertiliser with (15)N in the ammonium position; chlorophyll a was used as an indirect marker for algal activity, and ergosterol as an indirect marker of fungal activity. Nitrogen uptake was higher in E. prunastri than in X. parietina, although the latter species may have used the mannitol reserves to obtain C skeletons and energy for N assimilation. Chlorophyll a and ergosterol concentrations remained unaltered in X. parietina irrespective of N dosage while ergosterol decreased with increasing N uptake in E. prunastri. The latter species had accumulated a large pool of ammonium at the highest N dosage, whilst in X. parietina a significant nitrate pool was instead observed. Taken together, these short-term responses to high N supply observed in the two lichens, and the differences between them, can partly explain the higher tolerance of X. parietina towards increased atmospheric N levels.

Ammonium uptake in the nitrophytic lichen Xanthoria parietina and its effects on vitality and balance between symbionts

The aim of this investigation was to determine the NH4Cl concentration threshold, above which negative physiological effects would occur in the nitrophytic lichen Xanthoria parietina. Over a 10 month period, X. parietina thalli growing on roof tiles were exposed weekly to NH4Cl concentrations of 0·04, 0·17, 0·34 or 0·69 M. Nitrogen (N) uptake from ammonium and the concentrations of total thallus N and biont markers (chlorophyll a, ergosterol and chitin) were measured on four occasions, over the experimental period. Xanthoria parietina was able to assimilate a significant quantity of the applied ammonium. However, lichens exposed to the two higher concentrations suffered damage to both the photobiont and the mycobiont, as evidenced by reduced chlorophyll a and ergosterol concentrations, while lichens exposed to the two lower concentrations showed no significant changes in either chlorophyll a or ergosterol that could be related to the ammonium inputs. Xanthoria parietina tolerated a weekly irrigation of at least 0·17 M NH4Cl, corresponding to an N deposition of c. 1000 kg ha−1 yr−1, suggesting that this species has a very high tolerance to N pollution.

HOW AGRICULTURE AFFECTS LICHEN VEGETATION IN CENTRAL SWITZERLAND

The results from several floristic and bioindication projects in Central Switzerland (1986–1998), focusing on the effects of agriculture, particularly from nitrogen and agrochemical emissions, are summarized. The abundance of nutrient-tolerant lichen species and the decreased occurrence of nitrophytic lichens are both correlated with agricultural land use and high atmospheric deposition. The impact could be demonstrated not only by the distribution patterns of nutrient-tolerant species, but also by the high N content of lichens such asPhyscia caesia. Positive growth response ofCetraria islandicato application of mineral nutrients and increased CO2in open-top chambers at high altitudes was also observed. The methods and a survey of the results from studies conducted within the framework of the lichen research programme of the Natural History Museum of Lucernce are presented here. A discussion of the issues shows the need for further studies concenring the influence of introduced nutrients on the biodiverisyt of lichens.

Effects of atmospheric NH 3 on epiphytic lichens in the Netherlands : the pitfalls of biological monitoring

The lichen monitoring programme included in the Dutch National Air Quality Survey was used to explore the utility of these organisms as indicators for atmospheric ammonia. Over the period 1977–1990 the “nitrophytic” species (assumed to occur optimally in N-rich habitats) strongly increased at the 150 monitoring stations of the network. Furthermore, a positive correlation was found between the occurrence of these species and local NH 3 concentrations. Earlier reports therefore proposed the use of nitrophytic lichens as bioindicators for NH 3 and considered their increase as an indication for increasing NH 3 concentrations. However, a more careful statistical analysis of the available data shows a strong impact of decreasing SO 2 levels on all epiphytic lichens, including the nitrophytic species. It is now clear that the “nitrophytic” species do respond to atmospheric NH 3, but their response to SO 2 is far stronger. Furthermore, chemical analysis of tree bark shows that nitrophytic lichen species do not respond directly to N levels, but are rather favoured by the high bark pH associated with high NH 3 levels. Three mechanisms are presented to explain the strong response of the nitrophytic lichens to decreasing SO 2 levels.

EFFECTS OF AGRICULTURE ON EPIPHYTIC LICHEN VEGETATION IN CENTRAL ITALY

The influence of agriculture, i.e., of fertilizers and ammonia emissions from crops and sheep grazing, on epiphytic lichen vegetation, and the use of nitrophytic lichen species in bioindication of air pollution were investigated in a geothermal area in central Italy. Floristic analysis showed that the lichen vegetation is only slightly influenced by agriculture. Analysis of the lichen data and chemico-physical parameters of tree bark supporting lichen growth failed to demonstrate marked differences between agricultural and non-agricultural sites, the higher total frequency of nitrophytic species in agricultural sites being the only parameter discriminating between the two site types. Bark nitrogen and pH were not discriminant. Factors determining the higher total frequency of nitrophytic species in agricultural sites may include dust impregnation of bark and the drier microclimate of trees in these sites. It is concluded that nitrophytic lichens can be included in the calculation of the Index of Atmospheric Purity in the study area.