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Lecanora muralis (Schreber) Rabenh., top-wall, Botanical Garden, Wü rzburg, Germany, 6 March, 1996. Diel courses of CO 2 exchange (upper panel), corresponding photosynthetic photon flux density (PPFD, second panel) and apparent PSII photosynthetic quantum yield (W) and calculated relative electron transport rate (ETR, third panel). Bottom panel: lichen net photosynthesis (CO 2exchange) in relation to electron transport rate.
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Extensive investigations made in the past two decades on lichen photosynthesis in relation to water content have shown two features of particular interest: first, the depression of net photosynthesis at high water contents, suprasaturation (i.e. the lichen contains more water than necessary to saturate photosynthesis), and, second, the ability of g...
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Context 1
... the first daily course, presented for 6 March 1996 (Fig. 5), the lichen had been wetted the previous day and had a relatively constant respiratory rate throughout the night. During the day the lichen maintained a moderate WC. Apparent photosynthetic quantum yield (W, 1 s saturating light pulses; methods see Leisner et al., 1997) remained high and NP tracked incident PPFD reaching a maximal ...
Context 2
... see Leisner et al., 1997) remained high and NP tracked incident PPFD reaching a maximal value around 2 mmol m À2 s À1 at about 300 mmol m À2 s À1 PPFD. Respiration continued the following night showing that the lichen had not dried out. Calculated ETR was almost linearly related to NP during this day, when the lichen was not suprasaturated (Fig. 5, lower ...
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... For example, the distribution of the maximum water holding capacity in a lichen and bryophyte community may affect carbon sequestration by these communities, since it will affect community hydrology and thereby the duration of the metabolic activity (Lange et al., 2001). Because of such effects of functional trait distributions, there has been increasing interest in exploring the functional composition of lichen and bryophyte communities. ...
1. Environmental filtering and competition are two fundamental processes that shape plant community assembly in terms of functional composition, that is, the distribution of trait values. Understanding the role of these two processes in the assembly of non-vascular vegetation, such as bryophytes and lichens, is important since these communities provide essential ecosystem services in many regions around the world, and these depend on functional composition. Responses of non-vascular communities to environmental selection pressures have been explored in a range of experimental and modelling studies. However, it is still largely unknown to what extent competition affects the distribution of functional traits of non-vascular communities. Moreover, it remains poorly explored which traits that are associated with competition are key for shaping community functional assembly.
2. Here, we integrated a field transplantation experiment with a process-based model to disentangle the effects of environmental filtering and competition on the assembly of non-vascular communities. Following the validation of environmental selection in the model using field observations, we performed a simulation experiment to understand the impacts of competition on trait distributions in non-vascular communities growing in two temperate locations that differ in microclimatic conditions (a shaded and an open location).
3. Our results suggest that the functional composition is likely a result of weak competition or may not depend on competitive exclusion at all while environmental filtering plays an essential role. Plant height seems to be a key trait for competition. However, no single-trait competition scheme could consistently explain the observed functional composition of the studied non-vascular communities.
4. Synthesis. The presented model provides a new trait-based approach for simulating the functional assembly of non-vascular communities. Environmental filtering appears to be more essential than competition for predicting trait distributions of non-vascular communities under temperate climatic conditions and we recommend caution in associating competition to a single trait while analysing community functional assembly.
... Two incubation experiments were carried out to measure the EL gas exchange. This approach enables the determination of key parameters, such as the net CO 2 photoassimilation rates and the CO 2 losses associated with dark respiration and photorespiration, which are fundamental processes that characterize lichen growth and their ability to adapt to changing environmental conditions, such as humidity, temperature, and anthropogenic pollution [48][49][50]. A one-day aerobic preincubation was conducted at room temperature, during which the incubation jars were covered with lids to maintain a controlled environment. ...
Because they are widespread and evolutionarily old, epiphytic lichens (ELs) play an important role in global forest ecosystems. ELs are abundant in Siberian forest ecosystems, which are highly vulnerable to climate change; thus, ELs can be important contributors to the carbon (C) cycle. This study aims to address the unknown role of tree-inhabiting ELs in the C cycle of forest ecosystems in Central Siberia, where the EL biomass ranges from 492 to 3200 kg per ha. The main finding of this study is that ELs in a hydrated state can generate CH 4 for an extended period (at least two weeks), as determined by an incubation method. At the same EL moisture level, EL CO 2 fluxes are species-specific. The pattern of the release or uptake of GHGs by ELs may also alter due to climate change, e.g., changes in precipitation regimes (such as more frequent extreme rainfalls and droughts). Therefore, the EL contribution to the C cycle in forest ecosystems should be assessed, e.g., via the modeling of C cycling. Furthermore, specific factors, such as the EL exposure on the phorophyte stem, the EL biodiversity, and the day/night GHG fluxes, should be considered for a more concise assessment of ELs' contribution to the C cycle of forest ecosystems and their response to ongoing and projected climate change.
... The phenomenon, therefore, can be considered broadly in the context of the entire ecological group of lichens and not only as the specificity of individual species (see also TABLE 1). This probably implies difference between spatial distribution of forest and generalist lichens, especially when taking into account the realities of the natural environment and field performance of lichens (see Jonsson Čabrajić et al. 2010;Lange et al. 2001;Pintado et al. 1997;Pirintsos et al. 2011). ...
Most epiphytic lichens demonstrate high specificity to a habitat type, and sensitive hygrophilous species usually find shelter only in close-to-natural forest complexes. Some of them are considered as old-growth forest and/or long ecological continuity indicators. To evaluate general links between the narrow ecological range and physiological traits, two distinct sets of model lichens, i.e., old-growth forest (Cetrelia cetrarioides (Duby) W.L. Culb. & C.F. Culb., Lobaria pulmonaria (L.) Hoffm., Menegazzia terebrata (Hoffm.) A. Massal.), and generalist (Flavoparmelia caperata (L.) Hale, Hypogymnia physodes (L.) Nyl., Parmelia sulcata Taylor) ones, were examined in terms of sensitivity to long-term desiccation stress (1-, 2-, and 3-month) and photosynthesis activation rate upon rehydration. Desiccation tolerance and response rate to rehydration are specific to a given ecological set of lichens rather than to a particular species. Noticeable delayed and prompt recovery of high photosynthetic activity of photosystem II (PSII) characterize these sets, respectively. At the same time, although a decrease in the potential quantum yield of PSII in lichen thalli with a relative water content (RWC) at the level of 25% was observed, the efficiency remained at a very high level for all species, regardless of habitat preferences. Among the examined lichens, the fluorescence emission parameters for F. caperata were the fastest toward equilibrium upon rehydration, both after a shorter and a longer period of desiccation stress. In contrast to generalist lichens, retrieving of photosynthesis after 3-month desiccation failed in old-growth forest lichens. In the long term, prolonged rainless periods and unfavorable water balance in the environment predicted in the future may have a severely limiting effect on hygrophilous lichens during growing season (also in the sense of species associations) and, at the same time, promote the development of generalists.
... By contrast, most rainfall events supersaturate the lichen with excess water creating a film outside lichen surfaces that blocks the CO 2 uptake pathways and thereby causes strong depression of photosynthesis (Lange and Tenhunen 1981). Temporal suprasaturation depression is frequently documented (e.g., Lange and Matthes 1981;Lange et al., 1993Lange et al., , 2001, but less is known about how long-lasting continuous rain affects epiphytic vegetation in situ. Bryophytes replace lichens on trees within the more intense spray zone from waterfalls (Nilsson et al., 2022), and river regulations reducing the discharge of water can result in a great decrease in hygrophilous bryophytes and an increase in lichens (Odland et al., 1991). ...
... Most lichens have an optimal water content for photosynthesis, which approximately corresponds to the respective species' internal water holding capacity (Solhaug et al., 2021) measured after removing external water by blotting (Gauslaa 2014). Lichens need water to activate photosynthesis, but too much water reduces the CO 2 uptake by suprasaturation depression (Lange and Matthes 1981;Lange et al. 1993Lange et al. , 2001. Growth chamber experiments show that continuous hydration over two weeks is detrimental to lichens, which need to dry at least once a day to perform well (e.g., Solhaug and Gauslaa 2004). ...
Epiphytic lichens are considered sensitive indicators of environmental change. Excess water is known to depress their photosynthesis, but the effect of long-lasting rain on species richness of epiphytic lichens is rarely reported. By annually repeated records of macrolichen species richness on tree trunks over a period of 33 years that included one long rainy season in year 2000, a strong decline in macrolichen richness on tree trunks was detected after the unusually wet autumn. Afterwards, the lichen richness slowly recovered, but had not yet fully recovered 19 years after the dieback. Thereby, long rainy periods can cause lasting depression in epiphytic lichen richness, and continuous rain should be considered a possible threat to lichens in regions like northern Europe where global change predicts enhanced rainfall frequency.
... With this method the samples were not exposed to outside chamber conditions that might cause changes in gas-exchange rates. Further, our rehydration system allows gradual increase in relative humidity through an air humidifier module before any liquid water is addeda valuable technique for the recovery of bryophytes and lichens (Lange et al., 2001;. When samples were rehydrated inside the chamber, for homogenous and thorough hydration, larger amount of water was added onto the samples, and without the external water blotting with tissue paper, that is usually done in rehydration experiments, this resulted with some external water that remained on the chamber walls and on the sample, despite the draining (but this largely depends also on the thallus structure). ...
Desiccation-rehydration studies in cryptogams constitute an important tool to understand the relation of key physiological traits with species stress tolerance and environmental adaptability. Real-time monitoring of responses has been limited by the design of commercial or custom measuring cuvettes and difficulties in experimental manipulation. We developed a within-chamber rehydration method that allows to rewater the samples rapidly, without the need to open the chamber and take out the sample for manual rehydration by the investigator. Data is collected in real-time and simultaneously with an infrared gas-analyzer (LICOR-7000), a chlorophyll fluorometer (Maxi Imaging-PAM) and a proton transfer reaction time-of-flight mass-spectrometer (PTR-TOF-MS) for volatile organic compound emissions. The system was tested on four cryptogam species with contrasting ecological distributions. No major errors or kinetics disruptions were found during system testing and measurements. Our within-chamber rehydration method improved accuracy, as measurement periods were not lacking, and repeatability of the protocol by reducing error variance in sample manipulation. This method provides an improved technique to conduct desiccation-rehydration measurements, contributing to the standardization and accuracy of current existing methodologies. A close real-time and simultaneous monitoring of photosynthesis, chlorophyll fluorescence and volatile organic compound emission data, offers a novel perspective in the analysis of the cryptogam stress responses that is yet to be fully explored.
... In contrast, most bryophytes are reliant on liquid water (Proctor 2000;Proctor et al. 2007), mostly from rainfall (Proctor 2000), but also from dew (Csintalan et al. 1999), or cloud droplets (Leon-Vargas et al. 2006). Second, for lichens, oversaturation with water can limit photosynthesis via limited CO 2 diffusion (Lange et al. 1993(Lange et al. , 2001, whereas most bryophytes can thrive under continuously wet conditions (Proctor 2000). Finally, net photosynthesis is positive at a lower and narrower range of temperatures for lichens (Palmqvist 2008) than for bryophytes (Furness and Grime 1982;Liu et al. 2001). ...
Based on hypotheses related to environmental filtering vs. stochastic community assembly, we tested taxon-specific predictions regarding the relationships of alpha diversity, beta diversity and species composition of epiphytic macrolichens and bryophytes with elevation and the lateral gradient on trees (the different sides of the tree bole related to aspect and trunk inclination) at Parc national du Mont-Mégantic in Southeastern Québec, Canada. For lichens on firs, increasing elevation was associated with increasing alpha diversity, and a marked shift in community composition, at the scale of whole trees. In contrast, for bryophytes on maples, tree inclination and the lateral gradient had the strongest effects: more inclined trees had greater whole-tree alpha diversity and stronger within-tree contrasts in composition between the upper and lower bole surfaces. For lichens on maples, whole-tree alpha diversity showed a weak, negative relationship with inclination, and beta diversity increased slightly with elevation. Our results are consistent with theories predicting greater alpha diversity in more favorable environments (for lichens: high elevation with high relative air humidity and lower temperatures; for bryophytes: upper surfaces of tree boles with liquid water available), but support was weak for the prediction of greater beta diversity in more favorable environments. Overall, the important predictors of epiphytic cryptogam diversity vary more among the species of tree host (maple vs. fir) than focal taxa (lichens vs. bryophytes), with patterns likely related to different effects of water, temperature, and competition between lichens and bryophytes.
... The impacts of frost and drought are similar in that they limit free water availability for physiological activity (Lenne et al., 2010;Verhoeven et al., 2018). Cryptogams have the ability to quickly regain water, even from the atmosphere (Lange et al., 2001), to restart physiological activity (Bjerke et al., 2013;Kappen, 1993;Proctor et al., 2007). This ability allows for great physiological flexibility and their survival in high polar deserts (Kappen, 2000;Perera-Castro et al., 2021;Sancho et al., 2019). ...
Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (3 bryophytes, 4 lichens) to single events and factorial combinations of mid-winter heatwave (6°C for 7 days), re-freezing, snow removal and summer nitrogen addition. We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, were not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities. This article is protected by copyright. All rights reserved.
... Low YPSII is a consequence of suboptimal intrathalline CO 2 concentration caused by limitation in the diffusion of CO 2 molecules in fully hydrated cyanolichen thalli. It is believed that exopolysacharidic cellular envelopes in cyanobacteria and their high diffusion resistance for CO 2 in a fully hydrated state are the underlying mechanism causing the supersaturation effect [26]. Recently, we showed that in several Antarctic lichen species in natural conditions, the dehydrationdependent drop in FV/FM and YPSII was species-specific, starting at an RWC range of 22-32%. ...
Climate warming in the Antarctic tundra will affect locally dominant cryptogams. Being adapted to low temperatures and freezing, little is known about the response of the polar lichens’ primary photochemistry to warming and desiccation. Since 2008, we have monitored the ecophysiological responses of lichens to the future warming scenario during a long-term warming experiment through open top chambers (OTCs) on Fildes Peninsula. We studied the primary photochemical response (potential Fv/Fm and effective efficiency of photosystem II YPSII) of different lichen taxa and morphotypes under desiccation kinetics and heat shock experiments. As lichens grow slowly, to observe changes during warming we methodologically focused on carbon and nitrogen content as well as on the stable isotope ratios. Endemic Himantormia lugubris showed the strongest effect of long-term warming on primary photochemistry, where PSII activity occurred at a lower %RWC inside the OTCs, in addition to higher Fv/Fm values at 30 °C in the heat shock kinetic treatment. In contrast, Usnea aurantiaco-atra did not show any effect of long-term warming but was active at a thallus RWC lower than 10%. Both Cladonia species were most affected by water stress, with Cladonia aff. gracilis showing no significant differences in primary photochemical responses between the warming and the control but a high sensibility to water deficiency, where, at 60% thallus RWC, the photochemical parameters began to decrease. We detected species-specific responses not only to long-term warming, but also to desiccation. On the other hand, the carbon content did not vary significantly among the species or because of the passive warming treatment. Similarly, the nitrogen content showed non-significant variation; however, the C/N ratio was affected, with the strongest C/N decrease in Cladonia borealis. Our results suggest that Antarctic lichens can tolerate warming and high temperature better than desiccation and that climate change may affect these species if it is associated with a decrease in water availability
... Lichens not only tolerate but require regular cycles of wetting and drying (Armstrong, 1976). Prolonged saturation, by contrast, can be physiologically limiting by slowing CO 2 and O 2 diffusion (Lange et al., 2001), particularly for phototrophs lacking mechanisms to counteract this (see Section VII). ...
Lichens are the symbiotic outcomes of open, interspecies relationships, central to which are a fungus and a phototroph, typically an alga and/or cyanobacterium. The evolutionary processes that led to the global success of lichens are poorly understood. In this review, we explore the goods and services exchange between fungus and phototroph and how this propelled the success of both symbiont and symbiosis. Lichen fungal symbionts count among the only filamentous fungi that expose most of their mycelium to an aerial environment. Phototrophs export carbohydrates to the fungus, which converts them to specific polyols. Experimental evidence suggests that polyols are not only growth and respiratory substrates but also play a role in anhydrobiosis, the capacity to survive desiccation. We propose that this dual functionality is pivotal to the evolution of fungal symbionts, enabling persistence in environments otherwise hostile to fungi while simultaneously imposing costs on growth. Phototrophs, in turn, benefit from fungal protection from herbivory and light stress, while appearing to exert leverage over fungal sex and morphogenesis. Combined with the recently recognized habit of symbionts to occur in multiple symbioses, this creates the conditions for a multiplayer marketplace of rewards and penalties that could drive symbiont selection and lichen diversification.
... Estimating of parameters of primary photosynthesis based on the analysis of chlorophyll fluorescence (CF) induction kinetics (including parameters of 'fast' and stationary phases of inductive curves) is extensively applied in lichen biology in order to access the physiological state of these supraorganismal systems (Lange et al. 2001;Kalaji et al. 2016; Barták 2014;Stirbet et al. 2014;Goltsev et al. 2016;Palharini et al. 2020;Kuusinen et al. 2020). These parameters largely depend on the environmental conditions, embracing the presenceof pollutants and physiological conditions . ...
... On the one hand, the assimilation efficiency depends on intrathalline CO 2 availability which is affected by hydration status of the thallus (Lange et al. 2006(Lange et al. 1999. These data may be obtained from the experiments of CO 2 exchange measurements as a function of lichen water potential (Lange et al. 2001). On the other hand, it depends on the primary processes of photosynthesis. ...
The measurements of chlorophyll fluorescence play an important role in studies of lichen physiology. Usually, for foliose lichens fluorescence kinetics is recorded from the upper thalline side often exhibiting green color reflecting the presence of photosynthetic pigments. The lower side of such lichens is grey, dark-brown or black. At the first time, we evaluated photosynthetic activity distribution by chlorophyll fluorescence analysis on both lower and upper thallus sides for the foliose lichen Nephroma arcticum. We have demonstrated that photosynthesis proceeds not only on the green-colored upper side, but also on the gray lower side of the curled growing edges of the thallus lobes. These sides were differed in terms of PSII photochemical quantum yield, activity of non-regulatory dissipation and non-photochemical quenching of excited chlorophyll states (NPQ). Upper side was characterized by higher maximal PSII efficiency, whereas the lower one of the curled edges was characterized by higher actual photochemical quantum yield during actinic light acclimation. NPQ was higher on the upper surface, whereas, on the lower side (of the curled edges) non-regulatory dissipation was predominant. In terms of photosynthetic activity measurements, these results show, that actinic and measuring light reached the layer of phycobiont despite its shielding by mycobiont hyphae. On the melanized lower side in the basal thalline zone attached to the substratum photosynthesis was not detected. Lower side demonstrated higher level of light scattering in the reflectance spectra. We believe that different photoprotective mechanisms against high light are crucial on the upper and lower sides: NPQ on the upper surface, and light scattering and shielding by mycobiont on the lower side. Possible biological role of photosynthesis on the lower side is discussed.
