The integrity of lichen cell membrane as a suitable parameter for monitoring biological effects of acute nitrogen pollution

Role of Squalene Epoxidase Gene (SQE1) in the Response of the Lichen Lobaria pulmonaria to Temperature Stress

Currently, due to the increasing impact of anthropogenic factors and changes in solar activity, the temperature on Earth is rising, posing a threat to biodiversity. Lichens are among the most sensitive organisms to climate change. Elevated ambient temperatures can have a significant impact on lichens, resulting in more frequent and intense drying events that can impede metabolic activity. It has been suggested that the possession of a diverse sterol composition may contribute to the tolerance of lichens to adverse temperatures and other biotic and abiotic stresses. The major sterol found in lichens is ergosterol (ERG); however, the regulation of the ERG biosynthetic pathway, specifically the step of epoxidation of squalene to 2,3-oxidosqualene catalyzed by squalene epoxidase during stress, has not been extensively studied. In this study, we used lichen Lobaria pulmonaria as a model species that is well known to be sensitive to air pollution and habitat loss. Using in silico analysis, we identified cDNAs encoding squalene epoxidase from L. pulmonaria, designating them as LpSQE1 for the mycobiont and SrSQE1 for the photobiont Symbiochloris reticulata. Our results showed that compared with a control kept at room temperature (+20 °C), mild temperatures (+4 °C and +30 °C) did not affect the physiology of L. pulmonaria, assessed by changes in membrane integrity, respiration rates, and PSII activity. An extreme negative temperature (-20 °C) noticeably inhibited respiration but did not affect membrane stability. In contrast, treating lichen with a high positive temperature (+40 °C) significantly reduced all physiological parameters. Quantitative PCR analysis revealed that exposing thalli to -20 °C, +4 °C, +30 °C, and +40 °C stimulated the expression levels of LpSQE1 and SrSQE1 and led to a significant upregulation of Hsps. These data provide new information regarding the roles of sterols and Hsps in the response of lichens to climate change.

Exploring the synergistic effects of amoxicillin and methylene blue on unsaturated lipid structures: A study of Langmuir monolayers and giant unilamellar vesicles

The potentially toxic effects of emerging pollutant mixtures often deviate from the individual compound effects, presenting additive, synergistic, or agonistic interactions. This study delves into the complex world of emerging pollutants' mixtures, with a particular focus on their potential impact on unsaturated lipid DOPC (1,2-dioleoyl-sn-glycerol-3-phosphocholine) structured as both monolayers and bilayers, which are valuable tools for mimicking cell membranes. Specifically, we examine the effects of two common types of pollutants: antibiotics (amoxicillin) and dyes (methylene blue). Utilizing Langmuir monolayers, our research reveals a synergistic effect within the pollutant mixture, as evidenced by pressure-area isotherms and polarization-modulated infrared reflection absorption spectroscopy. We identify the specific chemical interactions contributing to this synergistic effect. Furthermore, through contrast phase microscopy experiments on giant unilamellar vesicles (bilayer system), we find that the individual pollutants and the mixture exhibit similar molecular effects on the bilayer, revealing that the molecular size is a key factor in the bilayer-mixture of pollutant interaction. This highlights the importance of considering molecular size in the interactions with bilayer systems. In summary, our research dissects the critical factors of chemical interactions and molecular size concerning the effects of pollutants on DOPC, serving as simplified models of cell membranes. This study underscores the significance of comprehending the molecular effects of emerging pollutants on human health and the development of models for exploring their intricate interactions with cell membranes.

Do urban air pollutants induce changes in the thallus anatomy and affect the photosynthetic efficiency of the nitrophilous lichen Physcia adscendens?

Lichens are symbiotic organisms that are generally sensitive to air pollution due to their specific biological and physiological features. Physcia adscendens is a nitrophilous lichen well-known for being resistant to air pollution associated with progressive anthropopressure. The aim of this study was to investigate the effect of nitrogen oxides and suspended particulate matter (PM10 and PM2.5) on anatomical structure of the thallus and photobiont's photosynthetic efficiency in P. adscendens inhabiting sites that differ in terms of air pollution level and thereby to determine the relevance of these pollutants for shaping the structure of the thallus and the physiological condition of the photosynthetic partner. We found that P. adscendens from polluted sites had increased thickness of the algal layer and the larger size of the algae cells, but a much lower ratio of the algal layer to the whole thallus. Lichens from highly polluted sites had also higher photosynthetic efficiency, which indicates a relatively good physiological condition of the photobiont. This indicates that the photobiont of P. adscendens is well-adapted to function under air pollution stress which may contribute to its success in colonizing polluted sites. Both changes in the anatomy of the lichen thallus and the efficiency of photosynthesis may be related to the enrichment of the environment with nitrogen. The increased photosynthetic efficiency as well as investment in the size of photobiont cells and growth mycobiont hyphae confirms that P. adscendens is well-adapted to urban conditions; however, the mechanism behind those adaptations needs more focus in the context of global environmental changes.

Lichens as spatially transferable bioindicators for monitoring nitrogen pollution

Excess nitrogen is a pollutant and global problem that harms ecosystems and can severely affect human health. Pollutant nitrogen is becoming more widespread and intensifying in the tropics. There is thus a requirement to develop nitrogen biomonitoring for spatial mapping and trend analysis of tropical biodiversity and ecosystems. In temperate and boreal zones, multiple bioindicators for nitrogen pollution have been developed, with lichen epiphytes among the most sensitive and widely applied. However, the state of our current knowledge on bioindicators is geographically biased, with extensive research effort focused on bioindicators in the temperate and boreal zones. The development of lichen bioindicators in the tropics is further weakened by incomplete taxonomic and ecological knowledge. In this study we performed a literature review and meta-analysis, attempting to identify characteristics of lichens that offer transferability of bioindication into tropical regions. This transferability must overcome the different species pools between source information - drawing on extensive research effort in the temperate and boreal zone - and tropical ecosystems. Focussing on ammonia concentration as the nitrogen pollutant, we identify a set of morphological traits and taxonomic relationships that cause lichen epiphytes to be more sensitive, or more resistant to this excess nitrogen. We perform an independent test of our bioindicator scheme and offer recommendations for its application and future research in the tropics.

Combined effect of acute salt and nitrogen stress on the physiology of lichen symbiotic partners

Nitrogen pollution and excessive salinity are commonly regarded as one of the major environmental concerns in recent decades in many urban environments. Although in urban areas lichens are exposed to both salt and nitrogen stress, no studies have been conducted to date on the simultaneous impact and interaction of these factors on lichen physiology. The aim was to determine the effect of various combinations of NaCl and NH4NO3 doses on the physiology of epigeic lichen Cladonia rei. We also aimed to compare the response of lichens collected from polluted and unpolluted sites to verify whether lichens exposed to different levels of environmental stress in their native environment will react differently. The combined salt-nitrogen treatment caused significant disturbances in the integrity of cell membranes and chlorophyll fluorescence parameters. The most detrimental effect concerned the loss of cell membrane integrity, which suggests that this parameter can serve as a relevant indicator of acute salt-nitrogen stress incidents. Salt stress decreased the photosynthetic efficiency 1 h after exposure, but after 72 h, the FV/FM returned to the level characteristic of healthy lichens in experimental groups without and with small doses of ammonium nitrate. In contrast, recovery was not possible in combination with high nitrogen doses. This indicates that exposure to short-term salt stress in a nitrogen-poor environment only causes a temporary reduction in photosynthetic efficiency, but in urban eutrophic environments may have more serious consequences. The weakened physiological condition of the mycobiont manifested by an increased level of cell membrane damage and a persistent decrease in the photosynthetic efficiency of the photobiont in lichens growing along the roads may indicate an excess of nitrogen in the environment, enhanced by the effect of salt. Lichens collected from a heavy-metal-polluted habitat responded more strongly than those from an unpolluted habitat suggesting that in lichens previously affected by certain harmful factors, exposure to another stress factor may lead to greater disturbances. This is of particular importance for lichens inhabiting the vicinity of roads, since they are also under the influence of other pollutants emitted by road traffic.

Synthesis of lichen response to gaseous nitrogen: ammonia versus nitrogen dioxide

The dominant chemical form of nitrogen pollution in the atmosphere in the U.S. is shifting from oxidized nitrogen, primarily from combustion of fossil fuels, to reduced nitrogen from agricultural animal waste and fertilizer applications. Does it matter to lichens? In this synthesis, we characterize U.S. air concentrations of the most ubiquitous gaseous forms of reduced and oxidized nitrogen, NO2 and NH3, respectively, and their direct effects on lichens. In the U.S., the 3-year average (2017-2019) of the annual mean for each monitoring site ranges up to 56.4 μg NO2 m-3 (~30 ppb) and 6 μg NH3 m-3 (~9 ppb). The spatial coverage of current routine monitoring of NO2 and NH3 likely does not accurately represent exposures of NO2 to ecosystems in rural areas or capture spikes of NH3 concentrations proximal to intensive agriculture, which are documented to exceed 700 μg NH3 m-3 (~1000 ppb) for short durations. Both NO2 and NH3 can act as nutrients to lichens, but as exposures rise, both can cause physiological stress and mortality that then change community composition and diversity. There is a growing body of evidence that lichen community composition is altered at current levels of exposure in the U.S. with estimated no effect or lowest effect concentrations from <1-3 μg m-3 NO2 and <1 μg m-3 NH3. Better spatial characterization of both NO2 and NH3 concentrations, especially near intensive agriculture, would help to characterize the extent of the impacts across the U.S. These findings are discussed in the context of U.S. air pollution policy.

Non-Toxic Increases in Nitrogen Availability Can Improve the Ability of the Soil Lichen Cladonia rangiferina to Cope with Environmental Changes

Climate change and atmospheric nitrogen (N) deposition on drylands are greatly threatening these especially vulnerable areas. Soil biocrust-forming lichens in drylands can provide early indicators of these disturbances and play a pivotal role, as they contribute to key ecosystem services. In this study, we explored the effects of different long-term water availability regimes simulating climate changes and their interaction with N addition on the physiological response of the soil lichen Cladonia rangiferina. Three sets of this lichen were subjected to control, reduced watering, and reduced watering and N addition (40 kg NH₄NO₃ ha⁻¹ year⁻¹) treatments for 16 months. Finally, all samples were subjected to daily hydration cycles with N-enriched water at two levels (40 and 80 kg NH₄NO₃ ha⁻¹ year⁻¹) for 23 days. We found that reduced watering significantly decreased the vitality of this lichen, whereas N addition unexpectedly helped lichens subjected to reduced watering to cope with stress produced by high temperatures. We also found that long-term exposure to N addition contributed to the acclimation to higher N availability. Overall, our data suggest that the interactions between reduced watering and increased N supply and temperature have an important potential to reduce the physiological performance of this soil lichen.

Resilience of Epiphytic Lichens to Combined Effects of Increasing Nitrogen and Solar Radiation

Lichens are classified into different functional groups depending on their ecological and physiological response to a given environmental stressor. However, knowledge on lichen response to the synergistic effect of multiple environmental factors is extremely scarce, although vital to get a comprehensive understanding of the effects of global change. We exposed six lichen species belonging to different functional groups to the combined effects of two nitrogen (N) doses and direct sunlight involving both high temperatures and ultraviolet (UV) radiation for 58 days. Irrespective of their functional group, all species showed a homogenous response to N with cumulative, detrimental effects and an inability to recover following sunlight, UV exposure. Moreover, solar radiation made a tolerant species more prone to N pollution’s effects. Our results draw attention to the combined effects of global change and other environmental drivers on canopy defoliation and tree death, with consequences for the protection of ecosystems.

Effects of wet atmospheric nitrogen deposition on epiphytic lichens in the subtropical forests of Central China: Evaluation of the lichen food supply and quality of two endangered primates

Over the last few decades, the threat posed to biodiversity and ecosystem function by atmospheric nitrogen (N) deposition has been increasingly recognized. The disturbed nutrient balance and species composition of plants induced by higher N deposition can impact the biodiversity of the organisms that consume the plants. In this research, we implemented several experiments to estimate the effects of increased N deposition on the growth, survival, and nutrients of the dominant epiphytic lichens in the subtropical mountains in Central China to assess the lichen food amount and nutritional quality for two endangered primates endemic to China. Our results indicated that the thallus growth and propagule survival of the lichens were significantly decreased when nitrogen addition changed from 6.25 to 50.0 kg N·ha^-1·y^-1; it was also shown that lichen biomass could be decreased by 11.2%-70.2% when the deposition addition exceeded 6.25 kg N·ha^-1·y^-1. Further, our study revealed that increased nitrogen deposition also reduced the nutritional quality of the lichens via reducing the soluble protein and soluble sugar levels and increasing the fiber content, which would substantially affect the diet selection of the plants consumers in the region, particularly the populations of the two lichen-eating endangered primate species, Rhinopithecus roxellana and R. bieti. Our experimental study suggested that the nitrogen pollution derived from anthropogenic activities could cause cascading effects for the whole forest ecosystem of Central China; thus, more studies about nitrogen deposition in this region are required.

The impact of nitrogen deposition on photobiont-mycobiont balance of epiphytic lichens in subtropical forests of central China

Excessive nitrogen (N) deposition can impact lichen diversity in forest ecosystems, and this is a particular situation in China. Here, we examined the N uptake, assimilation, and the impact of excessive N deposition on the symbiotic balance of dominant epiphytic lichens in the subtropical forests in the Mts. Shennongjia of central China. The results show that lichen species took up, assimilated and utilized more ammonium than nitrate in a species-specific way, following the increase of N availability. The photobiont of the lichens decreased with the increase of N concentration following an initial increase, while the mycobiont response to the N addition was not apparent. Considerable variation in response to excessive N deposition exists among the lichen species. Usnea longissima could regulate its N uptake, resulting in a stable photobiont-mycobiont ratio among N treatments. In contrast, the photobiont-mycobiont ratio of other four lichens increased initially but decreased when N concentration exceeded a certain level, and N stress may have broken the balance between photobiont and mycobiont of these lichens. Our results suggest that most epiphytic lichens in subtropical forest of central China could uptake and assimilate more ammonium than nitrate and that the balance between photobiont and mycobiont of many epiphytic lichens might change with the increasing N deposition load, which could impact the lichen diversity of this forest ecosystem.

Heavy-metal tolerance of photobiont in pioneer lichens inhabiting heavily polluted sites

Heavy metals are known for their negative impact on the physiological processes of lichen photobiont. In spite of this, certain lichens are known to be effective pioneers of polluted sites. Cladonia cariosa, C. rei, and Diploschistes muscorum are prominent examples of lichens that spontaneously colonise post-industrial wastes. We examined the effect of total and intracellular Zn, Pb, Cd, As, Cu, and Ni accumulation in the thalli of these species on the physiological parameters of photobiont. Increased accumulation of Zn, Cd, Cu, and Ni in D. muscorum and of Zn and Ni in C. rei negatively affected contents of photosynthetic pigments, whereas concentrations of Pb had a positive effect in all lichen species. Moreover, pigment contents were positively associated with the concentrations of most examined elements in C. cariosa. The results indicate that even if chlorophyll contents reduced, its degradation does not progress. This suggests that metal stress may exert a negative effect on the synthesis rather than on the integrity of chlorophyll. Most importantly, lichen samples of each of the species from polluted sites proved to possess significantly higher F_V/F_M ratios than those from a reference site; moreover, the contents of elements of lichen thalli positively influenced this parameter. The efficient functioning of the algal component under heavy-metal stress conditions indicates that the examined lichens are well adapted to extremely contaminated substrates.

Integrity of lichen cell membranes as an indicator of heavy-metal pollution levels in soil

The epigeic lichens Cladonia rei and Diploschistes muscorum are effective heavy-metal-tolerant colonisers of highly polluted and disturbed sites. In this study we compare their bioaccumulation capacities, accumulation patterns, and responses to heavy-metal stress, as expressed in terms of cell membrane damage. We also aim at verifying the relationships between cell membrane damage and levels of soil pollution with heavy metals, and thereby to identify the bioindicative value of this physiological parameter. Total and intracellular concentrations of Zn, Pb, Cd, As, Cu, and Ni were measured in 140 samples of lichens and corresponding soil, collected from variously contaminated sites. Relative electrical conductivity (EC%) values were determined concurrently in the lichen samples. The studied lichens differ considerably in intracellular uptake susceptibility and the related reduction in membrane integrity. In C. rei thalli, more than half of Zn, Pb, Cd, and As loads are accumulated extracellularly, whereas D. muscorum exhibits a tendency towards intracellular accumulation of the same elements. This property is clearly reflected in cell membrane damage, which is considerably greater in the latter species irrespective of study site. This indicates that intracellular heavy-metal accumulation affects the level of cell membrane damage. Two soil pollution classes were distinguished for both lichens based on element contents in host-substrate samples. The losses of cell membrane integrity in lichen thalli are related to these classes. EC% values above 16 in C. rei and above 20 in D. muscorum suggest elevated levels of heavy metals in the soil. Consequently, this physiological parameter can serve as an early warning indicator for detection of elevated metal concentrations in soil. The biomonitoring method proposed here involves common and widespread lichen species and can be widely applied in post-industrial areas.

May the Diversity of Epiphytic Lichens Be Used in Environmental Forensics?

Epiphytic (tree inhabiting) lichens, well-known biomonitors of atmospheric pollution, have a great potential for being used in environmental forensics. Monitoring changes in biodiversity is a useful method for evaluating the quality of an ecosystem. Lichen species occurring within an area show measurable responses to environmental changes, and lichen biodiversity counts can be taken as reliable estimates of environmental quality, with high values corresponding to unpolluted or low polluted conditions and low values to polluted ones. Lichen diversity studies may be very useful in the framework of environmental forensics, since they may highlight the biological effects of pollutants and constitute the base for epidemiological studies. It is thus of paramount importance that great care is taken in the interpretation of the results, especially in the context of a rapidly changing environment and facing global change scenarios. For this reason, it seems advisable to produce several zonal maps, each based on different species groups, and each interpreted in a different way. This exercise could also be a valid support in the framework of a sensitivity analysis, to support or reject the primary results. In addition, a clear and formal expression of the overall uncertainty of the outputs is absolutely necessary.

δ15N of lichens reflects the isotopic signature of ammonia source

Although it is generally accepted that δ¹⁵N in lichen reflects predominating N isotope sources in the environment, confirmation of the direct correlation between lichen δ¹⁵N and atmospheric δ¹⁵N is still missing, especially under field conditions with most confounding factors controlled. To fill this gap and investigate the response of lichens with different tolerance to atmospheric N deposition, thalli of the sensitive Evernia prunastri and the tolerant Xanthoria parietina were exposed for ten weeks to different forms and doses of N in a field manipulation experiment where confounding factors were minimized. During this period, several parameters, namely total N, δ¹⁵N and chlorophyll a fluorescence, were measured. Under the experimental conditions, δ¹⁵N in lichens quantitatively responded to the δ¹⁵N of released gaseous ammonia (NH₃). Although a high correlation between the isotopic signatures in lichen tissue and supplied N was found both in tolerant and sensitive species, chlorophyll a fluorescence indicated that the sensitive species very soon lost its photosynthetic functionality with increasing N availability. The most damaging response to the different N chemical forms was observed with dry deposition of NH₃, although wet deposition of ammonium ions had a significant observable physiological impact. Conversely, there was no significant effect of nitrate ions on chlorophyll a fluorescence, implying differential sensitivity to dry deposition versus wet deposition and to ammonium versus nitrate in wet deposition. Evernia prunastri was most sensitive to NH₃, then NH₄⁺, with lowest sensitivity to NO₃^-. Moreover, these results confirm that lichen δ¹⁵N can be used to indicate the δ¹⁵N of atmospheric ammonia, providing a suitable tool for the interpretation of the spatial distribution of NH₃ sources in relation to their δ¹⁵N signal.

Effects of Nitrogen Dioxide on Biochemical Responses in 41 Garden Plants

Nitrogen dioxide (NO₂) at a high concentration is among the most common and harmful air pollutants. The present study aimed to explore the physiological responses of plants exposed to NO₂. A total of 41 plants were classified into 13 functional groups according to the Angiosperm Phylogeny Group classification system. The plants were exposed to 6 μL/L NO₂ in an open-top glass chamber. The physiological parameters (chlorophyll (Chl) content, peroxidase (POD) activity, and soluble protein and malondialdehyde (MDA) concentrations) and leaf mineral ion contents (nitrogen (N⁺), phosphorus (P⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), manganese (Mn²⁺), and zinc (Zn²⁺)) of 41 garden plants were measured. After NO₂ exposure, the plants were subsequently transferred to a natural environment for a 30-d recovery to determine whether they could recover naturally and resume normal growth. The results showed that NO₂ polluted the plants and that NO₂ exposure affected leaf Chl contents in most functional groups. Increases in both POD activity and soluble protein and MDA concentrations as well as changes in mineral ion concentrations could act as signals for inducing defense responses. Furthermore, antioxidant status played an important role in plant protection against NO₂-induced oxidative damage. NO₂ poses a pollution risk to plant systems, and antioxidant status plays an important role in plant protection against NO₂-induced oxidative damage. In conditions of strong air pollution, more evergreen plants may be considered in landscape design, particularly in seasonal regions. The results of this study may provide useful data for the selection of landscaping plants in NO₂ polluted areas.

Metal accumulation and physiological response of the lichens transplanted near a landfill in central Lithuania

Landfilling is the most widely used method for disposal of municipal waste. The waste disposal sites are a matter of concern due to their adverse effects on the environment and health. Lichen Evernia prunastri and Ramalina farinacea were used for biomonitoring the effect of air pollution around the largest municipal landfill in Lithuania. Lichen transplants were exposed for 3.5 months up to 400 m from the landfill. Accumulation of heavy metals, except Cd, did not showed relevant differences in samples between landfill and control. Potential quantum yield expressed as F_V/F_M in thalli was affected at the closest to the pollution source sites and the values were lower in comparison with the control. The conductivity of leachate and peroxidated membrane lipids (TBARS) increased in lichen material transplanted at sites facing the landfill.

Thalli Growth, Propagule Survival, and Integrated Physiological Response to Nitrogen Stress of Ramalina calicaris var. japonica in Shennongjia Mountain (China)

In this study, effects of nitrogen (N) availability on growth, survival of Ramalina calicaris var. japonica, and whether it respond nitrogen stress in an integrated physiological way was evaluated. Thalli growth and propagule survival, thalli N and phosphorus (P) content, and activity of phosphomonoesterase (PME) of R. calicaris var. japonica were determined in a field experiment. Its differentiate adsorption in ammonia and nitrate, the activity of glutamine synthetase (GSA) and nitrate reductase (NRA) also were investigated in a series of indoor experiments. The results showed that N deposition significantly decreased the growth and survival of this lichen, and the N sensitivity threshold was suggested at 6.0 kg N⋅ha^-1⋅y^-1. When the N deposition increased from 8.59 kg N⋅ha^-1⋅y^-1 to 14.24, 20.49, 32.99 and 57.99 kg N⋅ha^-1⋅y^-1, the growth rates of lichen thalli decreased by 26.47, 39.01, 52.18 and 60.3%, respectively; Whereas the survival rate of the lichen propagules decreased from 92.8% of control (0.0 kg N⋅ha^-1⋅y^-1) to 10.7% of 50.0 kg N⋅ha^-1⋅y^-1, when they were treated with 0.00, 6.25, 12.5, 25.0, and 50.0 kg N⋅ha^-1⋅y^-1 deposition. Compared with an adequate adsorption of ammonium N, no nitrate adsorption occurred when thalli was submerged in solution lower than 0.4 mM. Our results also suggested that thalli total nitrogen, N:P ratio increased with N availability, and the activity of PME was significantly correlated with thalli total nitrogen. These all indicated that phosphorus limitation occurred when R. calicaris var. japonica treated with higher nitrogen deposition. Compared with slightly effects of NRA, GSA of R. calicaris var. japonica responded nitrogen availability significantly; In addition, GSA and NRA negatively correlated with thalli growth rate and propagule survival significantly. These results indicated that nitrogen stress do decrease growth and survival of R. calicaris var. japonica, and lichen would be impacted by excess nitrogen in a integrated, not a fragmentary way, including nitrogen uptake, assimilation, even nutrient balance of nitrogen and phosphorous.

Short- and long-term freezing effects in a coastal (Lobaria virens) versus a widespread lichen (L. pulmonaria)

Lichens are considered freezing tolerant, although few species have been tested. Growth, a robust measure of fitness integrating processes in all partners of a lichen thallus, has not yet been used as a viability measure after freezing. We compared relative growth rates (RGR) after freezing with short-term viability measures of photo- and mycobiont functions in the coastal Lobaria virens and the widespread L. pulmonaria to test the hypothesis that low temperature shapes the coastal distribution of L. virens. Hydrated thalli from sympatric populations were subjected to freezing at -10, -20 and -40 °C for 5 h. The rate of cooling and subsequent warming was 5 °C h^-1. Short-term viability measures of photobiont (maximal photosystem II efficiency, effective PSII yield) and mycobiont viability (conductivity index), as well as subsequent RGR, were assessed. The exotherms showed that L. virens froze at -3 °C; L. pulmonaria, at -4 °C. Freezing significantly impaired short-term viability measures of both photo- and mycobiont, particularly in the coastal species. Lobaria pulmonaria grew 2.1 times faster than L. virens, but the short-term damage after one freezing event did not affect the long-term RGR in any species. Thereby, short-term responses were impaired by freezing, long-term responses were not. While the lacking RGR-responses to freezing suggest that freezing tolerance does not shape the coastal distribution of L. virens, the significant reported adverse short-term effects in L. virens may be aggravated by repeated freezing-thawing cycles in cold winters. In such a perspective, repeated freezing may eventually lead to reduced long-term fitness in L. virens.

Intra- and inter-specific variations in chitin in lichens along a N-deposition gradient

The mechanisms of nitrogen (N) tolerance in lichens are not yet fully understood. Here, we investigated how the increase of chitin content is related with N excess at inter- and intra-specific levels, by using species with differing ecological N tolerances (the tolerant Xanthoria parietina and Parmotrema hypoleucinum and the sensitive Evernia prunastri and Usnea sp.) and thalli of X. parietina and P. hypoleucinum from sites with different availabilities of N of agricultural origin (livestock), as confirmed by lichen N content and δ¹⁵N. Nitrogen, chitin (N-containing compound), and ergosterol contents were measured in lichen thalli. Nitrogen and chitin contents were higher in tolerant species than those in sensitive ones (inter-specific level) and in thalli collected from the N-polluted site than in thalli from the clean site (intra-specific level). We suggest that chitin contributes to N stress tolerance in lichens, and that excess N can be partially stored as chitin (non-toxic form) in the cell walls of tolerant species.

The cost of surviving nitrogen excess: energy and protein demand in the lichen Cladonia portentosa as revealed by proteomic analysis

Different nitrogen forms affect different metabolic pathways in lichens. In particular, the most relevant changes in protein expression were observed in the fungal partner, with NO ₃^- mostly affecting the energetic metabolism and NH ₄⁺ affecting transport and regulation of proteins and the energetic metabolism much more than NO ₃^- did. Excess deposition of reactive nitrogen is a well-known agent of stress for lichens, but which symbiont is most affected and how, remains a mystery. Using proteomics can expand our understanding of stress effects on lichens. We investigated the effects of different doses and forms of reactive nitrogen, with and without supplementary phosphorus and potassium, on the proteome of the lichen Cladonia portentosa growing in a 'real-world' simulation of nitrogen deposition. Protein expression changed with the nitrogen treatments but mostly in the fungal partner, with NO₃^- mainly affecting the energetic metabolism and NH₄⁺ also affecting the protein synthesis machinery. The photobiont mainly responded overexpressing proteins involved in energy production. This suggests that in response to nitrogen stress, the photobiont mainly supports the defensive mechanisms initiated by the mycobiont with an increased energy production. Such surplus energy is then used by the cell to maintain functionality in the presence of NO₃^-, while a futile cycle of protein production can be hypothesized to be induced by NH₄⁺ excess. External supply of potassium and phosphorus influenced differently the responses of particular enzymes, likely reflecting the many processes in which potassium exerts a regulatory function.

Mechanisms of nitrogen deposition effects on temperate forest lichens and trees

We review the mechanisms of deleterious nitrogen (N) deposition impacts on temperate forests, with a particular focus on trees and lichens. Elevated anthropogenic N deposition to forests has varied effects on individual organisms depending on characteristics both of the N inputs (form, timing, amount) and of the organisms (ecology, physiology) involved. Improved mechanistic knowledge of these effects can aid in developing robust predictions of how organisms respond to either increases or decreases in N deposition. Rising N levels affect forests in micro- and macroscopic ways from physiological responses at the cellular, tissue, and organism levels to influencing individual species and entire communities and ecosystems. A synthesis of these processes forms the basis for the overarching themes of this paper, which focuses on N effects at different levels of biological organization in temperate forests. For lichens, the mechanisms of direct effects of N are relatively well known at cellular, organismal, and community levels, though interactions of N with other stressors merit further research. For trees, effects of N deposition are better understood for N as an acidifying agent than as a nutrient; in both cases, the impacts can reflect direct effects on short time scales and indirect effects mediated through long-term soil and belowground changes. There are many gaps on fundamental N use and cycling in ecosystems, and we highlight the most critical gaps for understanding potential deleterious effects of N deposition. For lichens, these gaps include both how N affects specific metabolic pathways and how N is metabolized. For trees, these gaps include understanding the direct effects of N deposition onto forest canopies, the sensitivity of different tree species and mycorrhizal symbionts to N, the influence of soil properties, and the reversibility of N and acidification effects on plants and soils. Continued study of how these N response mechanisms interact with one another, and with other dimensions of global change, remains essential for predicting ongoing changes in lichen and tree populations across North American temperate forests.

Uptake and toxicity of glyphosate in the lichen Xanthoria parietina (L.) Th. Fr

This study investigated if treatment of the lichen Xanthoria parietina (L.) Th. Fr. with glyphosate caused uptake of this herbicide as well as physiological alterations. Samples were treated with Glifene SL®, a common commercial glyphosate-based herbicide, at the lowest recommended doses (3.6g/L) as well as with doses slightly higher than the highest suggested (36 g/L). The results clearly showed glyphosate uptake in X. parietina proportionally to the dose provided. Adverse physiological effects were evident on the photosynthetic apparatus (photosynthetic efficiency, chlorophyll a content, chlorophyll degradation) as well as on the fungal respiration rates and cell membrane integrity (ergosterol content, dehydrogenase activity) already after 24h from treatment, also at the low application dose. It is concluded that lichens are suitable organisms for monitoring unwanted biological effects from the application of glyphosate-based herbicides, as well as for detecting the accumulation of this compound in the biota, thus screening for its environmental fate.

Effects of acute NH3 air pollution on N-sensitive and N-tolerant lichen species

Lichens are sensitive to the presence of ammonia (NH3) in the environment. However, in order to use them as reliable indicators in biomonitoring studies, it is necessary to establish unequivocally the occurrence of certain symptoms following the exposure to NH3 in the environment. In this paper, we simulated an episode of acute air pollution due to the release of NH3. The biological effects of acute air pollution by atmospheric NH3 have been investigated using N-sensitive (Flavoparmelia caperata) and N-tolerant (Xanthoria parietina) species. Lichen samples were exposed to ecologically relevant NH3 concentrations for 8 weeks, simulating three areas of impact: a control area (2 μg/m(3)), an area of intermediate impact (2-35 μg/m(3)) and an area of high impact (10-315 μg/m(3)), with a peak of pollution reached between the fourth and fifth week. Ammonia affected both the photobiont and the mycobiont in F. caperata, while in X. parietina only the photosynthetic performance of the photobiont was altered after exposure to the highest concentration. In the photobiont of F. caperata we recorded chlorophyll degradation as indicated by OD435/415 ratio, decrease of the photosynthetic performance (as reflected by the maximum quantum yield of primary photochemistry FV/FM and the performance index PIABS); in the mycobiont, ergosterol reduction, membrane lipid peroxidation (as reflected by the increase of thiobarbituric acid reactive substances), alteration (decrease) of the secondary metabolite usnic acid. No effects were detected on caperatic acid and dehydrogenase activity. In X. parietina, the only signal determined by NH3 was the alteration of FV/FM and the performance index PIABS. The results suggest that physiological parameters in N-sensitive lichens well reflect the effects of NH3 exposure and can be applied as early indicators in monitoring studies.

Physiological changes of the lichen Parmotrema tinctorum as result of carbon nanotubes exposition

Carbon nanotubes (CNT) is one of the more abundant nanomaterial produced in the world. Therefore, it is desirable to access its effects in all environment compartments, in order to mitigate environmental distress. This study aims to verify the potential use of lichens - classical atmospheric pollution indicators - as biomonitors of carbon nanotubes aerosols. To examine cause-effect relationships, preserving environmental microclimatic parameters, the lichen Parmotrema tinctorum (Nyl.) Hale was transplanted to open top chambers where aerosols of CNT were daily added. Physiological parameters such as cell viability, photosynthetic efficiency, cell permeability as well as nanoparticle internalization were assessed. Carbon nanotubes exposure led to reduction on the cell viability of P. tinctorum. The treatment with 100µg/mL of MWCNT-COOH resulted in intracellular ion leakage, probably due to changes in membrane permeability. No alterations on photosynthetic efficiency were detected. Carbon nanotubes entrapment and internalization into the lichen thallus were observed. Short term exposition of CNT produced measurable physiological changes in P. tinctorum lichen. This suggests the possibility of use of lichens as models to assess the environmental impact (air related) of engineered nanomaterials.

Heavy element accumulation in Evernia prunastri lichen transplants around a municipal solid waste landfill in central Italy

This paper presents the results of a biomonitoring study to evaluate the environmental impact of airborne emissions from a municipal solid waste landfill in central Italy. Concentrations of 11 heavy elements, as well as photosynthetic efficiency and cell membrane integrity were measured in Evernia prunastri lichens transplanted for 4months in 17 monitoring sites around the waste landfill. Heavy element contents were also determined in surface soils. Analytical data indicated that emissions from the landfill affected Cd, Co, Cr, Cu, Ni, Pb, Sb and Zn concentrations in lichens transplanted within the landfill and along the fallout direction. In these sites moderate to severe accumulation of these heavy elements in lichens was coupled with an increase in cell membrane damage and decrease in photosynthetic efficiency. Nevertheless, results indicated that landfill emissions had no relevant impact on lichens, as heavy element accumulation and weak stress symptoms were detected only in lichen transplants from sites close to solid waste. The appropriate management of this landfill poses a low risk of environmental contamination by heavy elements.

Spatial variation of eco-physiological parameters in the lichen Pseudevernia furfuracea transplanted in an area surrounding a cement plant (S Italy)

Thalli of the lichen Pseudevernia furfuracea were transplanted for 3 months (November 2010-January 2011) at 61 monitoring sites around a cement plant near Castrovillari (Calabria, southern Italy). NH3, NO x and SO2 concentrations were monitored monthly in a subarea of 10 sites (SA10) where the cement plant was located. At the end of the exposure period, the integrity of cell membranes; membrane lipid peroxidation (thiobarbituric acid reactive substances, TBARS level); vitality (cell respiration); chlorophyll a; chlorophyll b; carotenoids; phaeophytization quotient; photosynthetic efficiency and thalli concentrations of Al, Ca, Mg, V and Fe were measured. NO x concentrations correlated with the site distance from the cement plant while NH3 concentrations correlated with lichen vitality within SA10. For the monitoring area as a whole, only Fe and Mg concentrations correlated with membrane lipid peroxidation, while TBARS levels showed a significant increase and chlorophyll a, chlorophyll b and carotenoids a significant decrease with respect to the lichen origin area. Multivariate analysis (detrended correspondence analysis, cluster analysis and multi-response permutation procedure) of the eco-physiological parameters × monitoring sites data set resulted in four clusters termed C1, C2, C3 and C4. The eco-physiological parameters were compared among the four clusters and lichen origin area by one-way ANOVA. An index of environmental favourableness (IEF) to lichens was calculated to evaluate the spatial recovery of impaired values of TBARS, chlorophyll a, chlorophyll b, xanthophylls + carotenoids and phaeophytization quotient. The results indicate that there is no clear spatial trend in mycobiont impairment even though the IEF values suggest a higher number of sites with low levels of membrane lipid peroxidation in the 2--3-km distance band from the cement plant (the outermost) than in the two other distance bands (0-1 and 1-2 km). The photobiont seems to be damaged mainly in the inner distance band of the study area as suggested by the gradual but significant recovery trend of pigment levels and phaeophytization quotient from the inner distance band to the outer one (as shown by the IEF values). Conversion of chlorophyll to phaeophytin probably is not the only process affecting pigment levels.

Uptake and acute toxicity of cerium in the lichen Xanthoria parietina

Environmental cerium (Ce) levels are likely to increase in the near future and monitoring of its biological effects will therefore be necessary. The aim of this study was to test if treatment of the lichen Xanthoria parietina with Ce-containing solutions (0.1mM, 1mM, 10mM and 100mM) causes Ce bioaccumulation (both extra- and intra-cellularly) as well as physiological (sample viability, membrane lipids peroxidation, photosynthetic performance, water-soluble proteins content) and ultrastructural alterations. The results showed that treatment with Ce solutions induces Ce bioaccumulation, both extra-cellularly and intra-cellularly, which in turn causes an acute toxicity, evident as decreased sample viability, marked decrease in the photosynthetic performance and important changes in the ultrastructure.

Temporal trends of element concentrations and ecophysiological parameters in the lichen Pseudevernia furfuracea transplanted in and around an industrial area of S Italy

This study investigated the temporal trends of element concentrations and ecophysiological parameters (integrity of cell membranes, membrane lipid peroxidation, and sample vitality) in thalli of the lichen Pseudevernia furfuracea transplanted in and around an industrial area of S Italy from May 2010 to May 2011, once every 3 months. Element accumulation at levels indicating that the atmosphere of the study area was polluted by most elements occurred only during the third trimester of exposure, and the ecophysiological parameter best reflecting this trend was sample vitality expressed in terms of activity of the enzyme dehydrogenase. Among the available climatological parameters, the different amount of rainfall during the exposure period may influence the results, especially the number of hours with rainfall >16 mm/day, which is the threshold between light-moderate and moderate-heavy rainfall in the Mediterranean area.

Biological effects of ammonia released from a composting plant assessed with lichens

In this study, we investigated whether ammonia emissions from industrial composting of organic waste may influence the surrounding environment, using lichens as bioindicators. To this purpose, samples of N-tolerant and N-sensitive lichens, namely Xanthoria parietina and Evernia prunastri, were transplanted for 1-3 months along transects at increasing distance (0-400 m) from a composting facility in Tuscany, Italy. Atmospheric concentrations of ammonia were measured using passive samplers. The physiological response of lichen transplants was investigated by means of the photosynthetic efficiency (measured as chlorophyll a fluorescence emission), the integrity of cell membranes (measured as electrolyte leakage), and sample viability (measured as enzymatic activity of dehydrogenase). Epiphytic lichen communities were investigated using biodiversity indices. The results showed decreasing concentrations of ammonia, from 48.7 μg/m(3) at the composting facility to 2.7 μg/m(3) at 400 m. The N-tolerant X. parietina was not affected and some physiological parameters even showed a higher performance, while the N-sensitive E. prunastri showed a reduced performance with increasing atmospheric concentrations approaching the source. A shift from lichen communities composed by meso-acidophilous species (actual condition) to more nitrophilous communities in the near future, approaching the composting facility is suggested. It is concluded that lichens can provide useful data for decision-makers to establish correct science-based environmentally sustainable waste management policies.

Lichens as sentinels for air pollution at remote alpine areas (Italy)

The present study was undertaken with the aim of using epiphytic lichens as sentinels for air pollution at two remote alpine sites (1,400 and 1,800 m above sea level (asl)) of NW Italy. The results indicated that the site at 1,800 m prompted for early warning indications of biological changes. Although levels of the many elements assayed in samples of the lichen Pseudevernia furfuracea (L.) Zopf, ranging from minor elements (e.g., Al) to ultra-trace (e.g., Pt), were at normal levels, indications of a slowly worsening environment were given by the lichen biodiversity and by damage to cell membranes. The analysis of Pb isotopic ratios suggested that the origin of Pb accumulated in lichens is not local, but linked to the long-range transport by air masses. It was concluded that the origin of pollutants is from air mass coming from the Po plain of Italy and from densely populated areas of Switzerland and France.

Inertia in an ombrotrophic bog ecosystem in response to 9 years' realistic perturbation by wet deposition of nitrogen, separated by form

Wet deposition of nitrogen (N) occurs in oxidized (nitrate) and reduced (ammonium) forms. Whether one form drives vegetation change more than the other is widely debated, as field evidence has been lacking. We are manipulating N form in wet deposition to an ombrotrophic bog, Whim (Scottish Borders), and here report nine years of results. Ammonium and nitrate were provided in rainwater spray as NH4 Cl or NaNO3 at 8, 24 or 56 kg N ha(-1)  yr(-1) , plus a rainwater only control, via an automated system coupled to site meteorology. Detrimental N effects were observed in sensitive nonvascular plant species, with higher cumulative N loads leading to more damage at lower annual doses. Cover responses to N addition, both in relation to form and dose, were species specific and mostly dependent on N dose. Some species were generally indifferent to N form and dose, while others were dose sensitive. Calluna vulgaris showed a preference for higher N doses as ammonium N and Hypnum jutlandicum for nitrate N. However, after 9 years, the magnitude of change from wet deposited N on overall species cover is small, indicating only a slow decline in key species. Nitrogen treatment effects on soil N availability were likewise small and rarely correlated with species cover. Ammonium caused most N accumulation and damage to sensitive species at lower N loads, but toxic effects also occurred with nitrate. However, because different species respond differently to N form, setting of ecosystem level critical loads by N form is challenging. We recommend implementing the lowest value of the critical load range where communities include sensitive nonvascular plants and where ammonium dominates wet deposition chemistry. In the context of parallel assessment at the same site, N treatments for wet deposition showed overall much smaller effects than corresponding inputs of dry deposition as ammonia.

Antimony toxicity in the lichen Xanthoria parietina (L.) Th. Fr

In this paper we tested if treating the lichen Xanthoria parietina with Sb-containing solutions causes Sb bioaccumulation as well as physiological and ultrastructural changes. Total and intracellular antimony content in Sb-treated samples increased progressively with increasing concentration in the treatment solutions. Incubation of X. parietina thalli with Sb at concentrations as low as 0.1mM caused a decrease in sample viability, measured as intensity of respiratory activity, and damage to cell membranes, expressed in terms of membrane lipid peroxidation, as well as ultrastructural changes such as plasmolysis, impairment of the thylakoid system of the alga and cytoplasmic lipid droplets. The photosynthetic system hardly responded, at least under the tested experimental conditions.

Nitrogen tolerance in the lichen Xanthoria parietina: the sensitive side of a resistant species

To investigate the mechanisms of nitrogen (N) tolerance in lichens, we examined the physiological responses to increased N availability in different functional groups. Thalli of the nitrophytic Xanthoria parietina (L.) Th.Fr. previously grown both in an N-poor environment (~2kgNha-1year-1) and in an N-rich environment (~52kgNha-1year-1) were compared with the oligotrophic species Evernia prunastri (L.) Ach. and Usnea sp. Lichens were submitted to ammonium treatments. Maximum PSII efficiency, redistribution of the ions between the intra- and extracellular compartments and potassium and magnesium concentrations were the parameters used to check for the effects of N supply. The buffering capacity of the lichen extracts was also determined in untreated lichen thalli to check if different lichen behaviours were due to their ability to maintain the pH. The results showed a more similar response between X. parietina from the N-poor environment and the N-sensitive species than between X. parietina from the N-poor and N-rich environments, suggesting that X. parietina achieved N-tolerance after long-term exposure to N-rich environment. These results are important in understanding the effects of chronic ammonium pollution on one of the most sensitive components of the ecosystem, linking physiological response and ecological consequences.

Physiological response of the epiphytic lichen Evernia prunastri (L.) Ach. to ecologically relevant nitrogen concentrations

This study investigated the physiological response of the epiphytic lichen Evernia prunastri to ecologically relevant concentrations of nitrogen compounds. Lichen samples were sprayed for 4 weeks either with water or 50, 150 and 500 μM NH(4)Cl. The integrity of cell membranes and chlorophyll a fluorescence emission (F(V)/F(M) and PI(ABS)) were analyzed. No membrane damage occurred after the exposure period. F(V)/F(M), a classical fluorescence indicator, decreased during the second week of treatment with 500 μM NH(4)Cl and the third week with 50 and 150 μM NH(4)Cl. PI(ABS), an overall index of the photosynthetic performance, was more sensitive and decreased already during the first week with 500 μM NH(4)Cl and the second week with 150 μM NH(4)Cl. Since E. prunastri has been exposed to ammonium loads corresponding to real environmental conditions, these findings open the way to an effective use of this species as early indicators of environmental nitrogen excess.

Antioxidant response of three Tillandsia species transplanted to urban, agricultural, and industrial areas

To evaluate the physiological response of Tillandsia capillaris Ruiz & Pav. f. capillaris, T. recurvata L., and T. tricholepis Baker to different air pollution sources, epiphyte samples were collected from a noncontaminated area in the province of Córdoba (Argentina) and transplanted to a control site as well as three areas categorized according to the presence of agricultural, urban, and industrial (metallurgical and metal-mechanical) emission sources. A foliar damage index (FDI) was calculated with the physiological parameters chlorophyll a, chlorophyll b, malondialdehyde (MDA), hydroperoxyconjugated dienes, sulfur (S) content, and dry weight-to-fresh weight ratio. In addition, electrical conductivity (E-cond), relative water content (RWC), dehydration kinetics (Kin-H(2)O), total phenols (T-phen), soluble proteins (S-prot), and activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase were determined. The parameters E-cond, FDI, SOD, RWC, and Kin-H(2)O can serve as suitable indicators of agricultural air pollution for T. tricholepis and T. capillaris, and CAT, Kin-H(2)O, and SOD can do the same for T. recurvata. In addition, MDA, T-phen, and S-prot proved to be appropriate indicators of urban pollution for T. recurvata. Moreover, FDI, E-cond, and SOD for T. recurvata and MDA for T. tricholepis, respectively, could be used to detect deleterious effects of industrial air pollution.

Physiological and chemical response of lichens transplanted in and around an industrial area of south Italy: relationship with the lichen diversity

The lichen Evernia prunastri (L.) Ach. has been exposed for 3 months in and around an industrial area of Mediterranean Italy for monitoring physiological (photosynthetic efficiency, membrane lipids peroxidation and cell membrane integrity) and chemical (bioaccumulation of the heavy metals Cr, Ni, Pb, V and Zn) effects and investigate the consistency with the environmental quality status depicted by the diversity of epiphytic lichens (index of lichen diversity (ILD)). The results showed that thalli transplanted close to the industrial area exhibited early stress symptoms, as revealed by the increase in electrical conductivity indicating a damage endured by lichen cell membranes. The electrical conductivity was inversely correlated with the diversity of epiphytic lichens recorded at the same sites. The ILD negatively correlated also with membrane lipid peroxidation and the rate of accumulation of Pb, V and Zn. Reciprocal correlations found among trace elements pinpointed vehicular traffic and metal processing in the industrial area as main sources. The damage endured by cell membranes was the best physiological indicator consistent with the air quality status depicted by the diversity of epiphytic lichens.

Do lichens have "memory" of their native nitrogen environment?

This study aimed to deepen the knowledge about intraspecific mechanisms regulating nitrogen tolerance in lichens to wet nitrogen deposition. Thalli of the nitrophilous lichen Xanthoria parietina were collected from environments with different nitrogen availabilities and immersed in 80 mL of ammonium sulphate (NH₄)₂SO₄ solutions with distinct concentrations (0, 0.025, 0.05 and 0.25 M) for 5 h per day during 3 days in a week. After each soaking event, lichens were air dried. After each treatment, maximal PSII efficiency, localization of ammonium ions, concentrations of K+ and Mg²+ and thalli buffer capacity were determined. Our results show that lichens are marked by their native nitrogen environment, since there were important differences between the physiological responses of X. parietina thalli previously grown in an area with high nitrogen deposition (nitrogen emissions of ca. 13,000 t/year) and those previously grown in an unpolluted area (nitrogen emissions of ca. 500 t/year). Greater N availability seems to enable X. parietina to cope better with the effects of nitrogen pollution.

Ammonium and nitrate tolerance in lichens

Since lichens lack roots and take up water, solutes and gases over the entire thallus surface, these organisms respond more sensitively to changes in atmospheric purity than vascular plants. After centuries where effects of sulphur dioxide and acidity were in the focus of research on atmospheric chemistry and lichens, recently the globally increased levels of ammonia and nitrate increasingly affect lichen vegetation and gave rise to intense research on the tolerance of lichens to nitrogen pollution. The present paper discusses the main findings on the uptake of ammonia and nitrate in the lichen symbiosis and to the tolerance of lichens to eutrophication. Ammonia and nitrate are both efficiently taken up under ambient conditions. The tolerance to high nitrogen levels depends, among others, on the capability of the photobiont to provide sufficient amounts of carbon skeletons for ammonia assimilation. Lowly productive lichens are apparently predisposed to be sensitive to excess nitrogen.