Modelling hydration and photosystem II activation in relation to in situ rain and humidity patterns: a tool to compare performance of rare and generalist epiphytic lichens

A dynamic water and activity model was developed to assess how efficiently lichens can exploit in situ rain and humid air. The capacity to rehydrate and activate photosynthesis [i.e. photosystem II (PSII)] by these water sources was compared among four hydrophilic and one generalist epiphytic lichen. Hydration status, potential (instant activation) and realized (delayed activation) day‐light activity were simulated using a model based on species‐specific hydration, PSII activation characteristics and in situ water content for Platismatia norvegica in three microclimatic scenarios. The results showed that delayed PSII activation could have profound effects on lichens' ability to exploit environmental water sources. During rain, realized activity was reduced by 19, 34 and 56% compared to simulations assuming instant activation for three hydrophilic lichens in the driest microclimate. During humid air, the reduction was 81% for the most extreme species and scenario, because of slow hydration and low equilibrium water content. Many and brief hydration events may thus hamper species with slow activation and fast desiccation kinetics. No evidence of compensation by a ‘water‐holding’ morphology was observed among studied species. The developed model may provide a tool for identifying suitable habitats for long‐term persistence of lichens with physiological constraints.     

Juvenile Development of the Cyanolichen Lobaria scrobiculata and the Green Algal Lichens Platismatia glauca and Platismatia norvegica in a Boreal Picea abies Forest

Abstract: Juvenile development from sown vegetative diaspores of the cyanobacterial lichen Lobaria scrobiculata and the green algal lichens Platismatia glauca and P. norvegica was studied through a four-year field experiment in a boreal spruce forest. All three species developed juvenile thalli within the period of observation. The largest lobules of L. scrobiculata and Platismatia were 0.4 mm and 1.3 mm, respectively, four years after sowing the diaspores. The first very tiny lobule (0.1 mm) of L. scrobiculata was observed 29 months after sowing the soredia. This period of juvenile development is the longest period so far reported for lichens. A long phase of dormancy, after the diaspores were attached to the substrate, was characteristic for the investigated species. Apical growth of the isidia of Platismatia glauca and P. norvegica was not observed until 21 months after sowing. Low light levels, low temperatures and snow covering the diaspores during winter, causes a short growth season in boreal spruce forests. These factors might explain the long period for juvenile development. The results indicate a slow rate of colonization of a new habitat for the investigated species since they need several years to grow to visible thalli.     

Functional trade-off of hydration strategies in old forest epiphytic cephalolichens

Although water is essential for photosynthetic activation in lichens, rates of vapor uptake and activation in humid air, which likely influence their niche preferences and distribution ranges, are insufficiently known. This study simultaneously quantifies rehydration kinetics and PSII reactivation in sympatric, yet morphologically and functionally distinct cephalolichens (Lobaria amplissima, Lobaria pulmonaria, Lobaria virens). High-temporal resolution monitoring of rehydrating thalli by automatic weighing combined with chlorophyll fluorescence imaging of maximal PSII efficiency (F_V/F_M) was applied to determine species-specific rates of vapor uptake and photosynthetic activation. The thin and loosely attached growth form of L. pulmonaria rehydrates and reactivates faster in humid air than the thick L. amplissima, with L. virens in between. This flexible hydration strategy is consistent with L. pulmonaria’s wide geographical distribution stretching from rainforests to continental forests. By contrast, the thick and resupinate L. amplissima reactivates slowly in humid air but stores much water when provided in abundance. This prolongs active periods after rain, which could represent an advantage where abundant rain and stem flow alternates with long-lasting drying. Understanding links between morphological traits and functional responses, and their ecological implications for species at risk, is crucial to conservation planning and for modelling populations under various climate scenarios.     

The paradox of higher light tolerance during desiccation in rare old forest cyanolichens than in more widespread co-occurring chloro- and cephalolichens

? Desiccation tolerance was quantified in four cyanolichens (Lobaria hallii, Lobaria retigera, Lobaria scrobiculata, Pseudocyphellaria anomala), one cephalolichen (Lobaria pulmonaria) and one chlorolichen (Platismatia glauca) from xeric and mesic, open and closed North American boreal forests. ? These sympatric epiphytes were exposed to 0%, 33%, 55% and 75% relative humidity with or without medium light (200?μmol?m(-2) s(-1) ) for 7?d. Permanent and temporary photoinhibitory damage was recorded as viability measures. ? All species tolerated well the drying in darkness, but L.?hallii and L.?retigera, associated with a very humid climate, showed minor damage at the hardest drying (silica gel). Simultaneous exposure to medium light severely aggravated the drying damage at all relative humidity levels. Combined drying-light exposure was particularly devastating for the widespread chloro- and cephalolichens, whereas cyanolichens, including rare old forest species, were fairly resistant. ? The ability to recover after combined drying-light stress (this study) correlated positively with increasing species-specific water holding capacities (from the literature). Cyanolichens, depending on liquid water and large internal water storage, probably require strong drying-light resistance to handle long periods between hydration events, whereas chlorolichens can regularly maintain their photosynthetic apparatus during frequent and rapid activation by humid air on clear mornings.     

Changing climate and historic‐woodland structure interact to control species diversity of the ‘Lobarion’ epiphyte community in Scotland

Question: How will changing climate and habitat structure interact to control the species diversity of lichen epiphytes? Location: Scotland. Method: Species richness (=diversity) of the epiphyte lichen community known as Lobarion (named after Lobaria pulmonaria) was quantified for 94 Populus tremula stands across Scotland, and compared in a predictive model to seven climate variables and eight measures of woodland structure. An optimum model was selected and used to project Lobarion diversity over the geographic range of the study area, based on IPCC climate change scenarios and hypothetical shifts in woodland structure. Results: Species diversity of the Lobarion community was best explained by three climate variables: (1) average annual temperature; (2) autumn and winter precipitation; in combination with (3) historic‐woodland extent. Projections indicate a positive effect of predicted climate change on Lobarion diversity, consistent with the physiological traits of cyanobac‐terial lichens comprising the Lobarion. However, the general response to climate is modified significantly by the effect on diversity of historic‐woodland extent. Conclusions: Historic‐woodland extent may exert an important control over local climate, as well as impacting upon the metapopulation dynamics of species in the Lobarion. In particular, a temporal delay in the response of Lobarion species to changed woodland structure is critical to our understanding of future climate change effects. Future Lobarion diversity (e.g. in the 2050s) may depend upon the interaction of contemporary climate (e.g. 2050s climate) and historic habitat structure (e.g. 1950s woodland extent). This is supported by previous observations for an extinction debt amongst lichen epiphytes, but suggests an extension of simple climate‐response models is necessary, before their wider application to lichen epiphyte diversity.     

Metabolic recovery of continental antarctic cryptogams after winter

The activation of metabolism after the winter period was investigated in several mosses and lichens in continental Antarctica. Thalli that were still in their over-wintering inactive state in early spring were sprayed artificially and the time-dependent activation of photosystem II (PSII), carbon fixation and respiration was determined using gas exchange and chlorophyll a fluorescence techniques. The investigated lichens recovered PSII activity almost completely within the first few minutes and gross photosynthesis was fully reactivated within a few hours. In contrast, photosynthesis took much longer to recover in mosses, which could indicate a general difference between the green-algal symbionts in lichens and moss chloroplasts. Only small and quickly reversible increased rates of respiration were observed for the foliose lichen Umbilicaria aprina from a more xeric habitat. In contrast, species occurring near persistent meltwater, such as the moss Bryum subrotundifolium and the lichen Physcia caesia, had highly increased respiration rates that were maintained for several days after activation. Calculation of the carbon balances indicated that the activation pattern strongly dictated the length of time before a carbon gain was achieved. It appears that the differences in recovery reflect the water relations of the main growth period in summer.     

Growth and vitality of epiphytic lichens

 We tested the hypothesis that changed microclimate at induced forest edges causes reduced growth of epiphytic lichens. Two foliose, green algal lichens were transplanted to the lower canopy of a mature Picea abies forest at six distances (2, 6.25, 12.5, 25, 50 and 100 m) from a clearcut. The biomass growth in Platismatia glauca (6.2% in 16 months) was 41% higher than in Lobaria pulmonaria (4.4%). We found no growth reduction near the forest edge. In contrast, the highest growth in both species occurred within 12 m from the edge. Further, fluorescence and chlorophyll measurements showed that lichen vitality was unaffected by distance from edge. The light intensity was 4.3 times higher at the edge than in the interior during the growing season, but there were only minor differences in air temperature and relative humidity. Monitoring of thallus water content revealed clear differences in both number and length of wetting and drying cycles. However, the total time with water content sufficient for photosynthetic activity was only slightly higher at the edge. The data thus indicate that our gradient in microclimate was too small to significantly affect lichen growth, and that lichens are largely metabolically inactive when large edge-interior contrasts in microclimate occur. Lichen response to forest edge microclimate results from intricate interactions among several biotic and abiotic factors. Linking data on lichen growth, microclimate and thallus water content with physiological measurements provides a framework for future studies of the mechanisms behind abiotic edge effects. Received: 15 April 1996 / Accepted: 21 June 1996     

Predicting lichen hydration using biophysical models

Two models for predicting the hydration status of lichens were developed as a first step towards a mechanistic lichen productivity model. A biophysical model included the water potential of the air, derived from measurements of air temperature, relative humidity and species-specific rate constants for desiccation and rehydration. A reduced physical model, included only environmental parameters, assuming instantaneous equilibration between the lichen and the air. These models were developed using field and laboratory data for three green algal lichens: the foliose epiphytic Platismatia glauca (L.) W. Culb., the fruticose epiphytic Alectoria sarmentosa (Ach.) Ach. and the fruticose, terricolous and mat-forming Cladina rangiferina (L.) Weber ex Wigg. The models were compared and validated for the same three species using data from a habitat with a different microclimate. Both models predicted the length and timing of lichen hydration periods, with those for A. sarmentosa and P. glauca being highly accurate—nearly 100% of the total wet time was predicted by both the biophysical and physical models. These models also predicted an accurate timing of the total realized wet time for A. sarmentosa and P. glauca when the lichens were wet. The model accuracy was lower for C. rangiferina compared to the epiphytes, both for the total realized wet time and for the accuracy of the timing for the hydration period. These results demonstrate that the stochastic and continually varying hydration status of lichens can be simulated from biophysical data. Further development of these models to also include water-related activity, light and temperature conditions during the hydration events will then be a potent tool to assess potential lichen productivity in landscapes and habitats of various microclimatic conditions.     

Sterols of three lichen species: Lobaria pulmonaria, Lobaria Scrobiculata and Usnea Longissima

Sterols were extracted from the lichens Lobaria pulmonaria, Lobaria scrobiculata and Usnea longissima with chloroform-methanol (2:1) (solvent-extractable fraction) followed by saponification of the residual lichen material to give a tightly-bound sterol fraction. The compounds were principally ergosterol, episterol, fecosterol and lichesterol with minor quantities of C₁₇, C₂₈ and C₂₉ monoenes and dienes of the phytosterol type.     

Defensive compound concentration in boreal lichens in response to simulated nitrogen deposition

Nitrogen (N) deposition is expected to increase in northwestern Europe the next 50–100 years. The effects of higher N availability on lichens will presumably depend on their capacity to acquire carbon (C), that is, of the timing and duration of the wet and active state. If lichens respond like plants, their C and N status may affect their concentration of carbon-based secondary compounds (CBSCs), and thus their defence against herbivores, detrimental radiation, pathogens and parasites. In the present study we have manipulated N availability and timing and duration of the metabolically active state by spraying lichen transplants in an old spruce forest with rainwater or rainwater with added N corresponding to 50 kg N ha⁻¹ yr⁻¹. The spraying was applied either at night, in the morning or at noon to also investigate the effect of timing and duration of the active state. Concentrations of N, chlorophyll a (Chl a ) and CBSCs were measured before and after one summer's spraying of 10 thalli in each of four different lichen species; Alectoria sarmentosa, Lobaria scrobiculata, Platismatia glauca , and Xanthoria aureola . The added N was readily taken up by all the lichen species. A. sarmentosa, P. glauca , and X. aureola increased their Chl a concentration in response to increased N, while L. scrobiculata increased Chl a in response to increased active time. None of the studied species reduced their concentration of secondary compounds during the experimental period, but in P. glauca the concentration of all compounds were significantly lower in N-treated thalli compared with those that got only rainwater. The results are consistent with a high degree of constitutive defence in three of four species, and we conclude that all the investigated lichens seem to have rather robust chemical defence systems despite considerable manipulation of the environmental conditions.     

Fine-scale distribution of the epiphytic lichen Usnea longissima on two even-aged neighbouring Picea abies trees

Abstract. Two neighbouring even-aged 130-yr old Picea abies trees in a homogeneous stand can differ substantially with respect to their epiphytic vegetation. Sampled branches from the canopy of one tree harboured 781 specimens of the old forest lichen Usnea longissima of which only 50 could be seen from the ground, whereas no U. longissima were found on its nearest neighbour. Usnea longissima was most abundant on branch tips in lower parts of the canopy on branch segments having the highest biomass of other alectorioid species. Trees with and without U. longissima showed a different pattern in their mineral composition, suggesting that a tree-specific difference in nutritional status might contribute to explain the patchy distribution of this lichen within seemingly homogeneous stands.     

Remnants fragments preserve genetic diversity of the old forest lichen <Emphasis Type="Italic">Lobaria pulmonaria</Emphasis> in a fragmented Mediterranean mountain forest

Fragmentation represents a serious threat to biodiversity worldwide, however its effects on epiphytic organisms is still poorly understood. We study the effect of habitat fragmentation on the genetic population structure and diversity of the red-listed epiphytic lichen, Lobaria pulmonaria, in a Mediterranean forest landscape. We tested the relative importance of forest patch quality, matrix surrounding fragments and connectivity on the genetic variation within populations and the differentiation among them. A total of 855 thalli were sampled in 44 plots (400 m²) of 31 suitable forest fragments (beeches and oaks), in the Sierra de Ayllón in central Spain. Variables related to landscape attributes of the remnant forest patches such as size and connectivity and also the nature of the matrix or tree species had no significant effects on the genetic diversity of L. pulmonaria. Values of genetic diversity (Nei’s) were only affected by habitat quality estimated as the age patches. Most of the variation (76%) in all populations was observed at the smallest sampled unit (plots). Using multiple regression analysis, we found that habitat quality is more important in explaining the genetic structure of the L. pulmonaria populations than spatial distance. The relatively high level of genetic diversity of the species in old forest patches regardless of patch size indicates that habitat quality in a highly structured forest stand determines the population size and distribution pattern of this species and its associated lichen community. Thus, conservation programmes of Mediterranean mountain forests have to prioritize area and habitat quality of old forest patches.     

LICHEN PENDANTS FOR TRANSPLANT AND GROWTH EXPERIMENTS

Lichens were cultured by attaching a thallus fragment to a nylon monofilament loop with silicone sealer. Two effective methods for adjusting lichen mass to a standard moisture content were developed (the ‘reference-sample’ and ‘sacrificial’ methods). These corrections for moisture content allow detection of very small changes in dry mass without having to oven dry (and kill) all transplants. Average annual biomass growth rates for non-fragmenting species were typically between 5 and 30%. Annual biomass growth rates of healthy, vigorous individuals, as indicated by the 75th percentile, were mostly between 10 and 40%.Alectoria sarmentosawas prone to fragmentation despite the maintenance of healthy thalli. The other species can be ranked by biomass growth rates as follows:Evernia prunastri>Lobaria pulmonaria=Usnea longissima>Pseudocyphellaria rainierensis=Lobaria oregana. 1996 The British Lichen Society     

Is local distribution of the epiphytic lichen <Emphasis Type="Italic">Lobaria pulmonaria</Emphasis> limited by dispersal capacity or habitat quality?

By surveying and re-surveying 12 forest sites in southern Sweden for the epiphytic lichen Lobaria pulmonaria with a 9-year interval, and measuring tree-related habitat quality variables, we have investigated whether the local distribution of the lichen is limited by poor dispersal capacity or by habitat quality. Dispersal distances were measured indirectly as the distances between colonised trees and the nearest trees occupied by L. pulmonaria in both 1992 and 2001. To compare habitat quality between trees occupied by L. pulmonaria and neighbouring control trees, we recorded tree species and measured age and growth rate of trees, light conditions, bark structure and bryophyte cover. The estimated mean dispersal distance was 35 m, with a recorded maximum of 75 m. Occupied trees were larger and had a larger cover of bryophytes than unoccupied trees of similar size. The results indicate that dispersal capacity probably is the most important factor in limiting the local distribution of L. pulmonaria, but habitat-quality factors may be important on a smaller spatial scale.     

Functional responses in the habitat selection of a generalist mega‐herbivore,the African savannah elephant

Resource selection function (RSF) models are commonly used to quantify species/habitat associations and predict species occurrence on the landscape. However, these models are sensitive to changes in resource availability and can result in a functional response to resource abundance, where preferences change as a function of availability. For generalist species, which utilize a wide range of habitats and resources, quantifying habitat selection is particularly challenging. Spatial and temporal changes in resource abundance can result in changes in selection preference affecting the robustness of habitat selection models. We examined selection preference across a wide range of ecological conditions for a generalist mega‐herbivore, the African savanna elephant Loxodonta africana, to quantify general patterns in selection and to illustrate the importance of functional responses in elephant habitat selection. We found a functional response in habitat selection across both space and time for tree cover, with tree cover being unimportant to habitat selection in the mesic, eastern populations during the wet season. A temporal functional response for water was also evident, with greater variability in selection during the wet season. Selection for low slopes, high tree cover, and far distance from people was consistent across populations; however, variability in selection coefficients changed as a function of the abundance of a given resource within the home range. This variability of selection coefficients could be used to improve confidence estimations for inferences drawn from habitat selection models. Quantifying functional responses in habitat selection is one way to better predict how wildlife will respond to an ever‐changing environment, and they provide promising insights into the habitat selection of generalist species.     

Comparative phylogeography of two co‐distributed but ecologically distinct rainbowfishes of far‐northern Australia

Aim

To test the influence of historical and contemporary environment in shaping the genetic diversity of freshwater fauna we contrast genetic structure in two co‐distributed, but ecologically distinct, rainbowfish; a habitat generalist (Melanotaenia splendida) and a habitat specialist (M. trifasciata).

Location

Fishes were sampled from far northern Australia (Queensland and Northern Territory).

Methods

We used sequence data from one mitochondrial gene and one nuclear gene to investigate patterns of genetic diversity in M. splendida and M. trifasciata to determine how differences in habitat preference and historical changes in drainage boundaries affected patterns of connectivity.

Results

Melanotaenia splendida showed high levels of genetic diversity and little population structure across its range. In contrast, M. trifasciata showed high levels of population structure. Whereas phylogeographic patterns differed, both species showed a strong relationship between geographical distance and genetic differentiation between populations. Melanotaenia splendida showed a shallower relationship with geographical distance, and genetic differentiation was best explained by stream length and a lower scaled ocean distance (11.98 times coast length). For M. trifasciata, genetic differentiation was best explained by overwater distance between catchments and ocean distance scaled at 1.16 × 10⁶ times coast length.

Main conclusions

Connectivity of freshwater populations inhabiting regions periodically interconnected during glacial periods appears to have been affected by ecological differences between species. Species‐specific differences are epitomized here by the contrast between co‐distributed congeners with different habitat requirements: for the habitat generalist, M. splendida, there was evidence for greater historical genetic connectivity with oceans as a weaker barrier to gene exchange in contrast with the habitat specialist, M. trifasciata.     

Extreme specialization to rocky habitats in Tropidurus lizards from Brazil: Trade‐offs between a fitted ecomorph and autoecology in a harsh environment

Ecomorphological theory indicates that different ecological requirements lead to different organismal designs. Given that species with equal requirements could not coexist, traits leading to more efficient use of resources may be selected to avoid competition among closely related syntopic species, generating specialized ecomorphs. We compared habitat use, diet, thermal biology and morphology among the syntopic Tropidurus semitaeniatus, T. helenae and T. hispidus in the Caatinga of Northeastern Brazil. Tropidurus semitaeniatus and T. helenae are flattened lizards specialized to rocks and rock crevices, whereas T. hispidus has a robust body and generalist habits. We aimed to test the hypothesis that morphological modifications observed in the flattened ecomorphs are related to modifications in diet and habitat use. Also, we hypothesized that specialization to habitat induces morphological modifications, which in turn may constrain lizard performance. Flattened species differed in habitat use, morphology and prey size when compared with the generalist ecomorph. Morphological modifications were related to specializations to rocky habitats and constrained the variety of prey items consumed. This phenotype also reduced their reproductive output when compared with a robust, generalist ecomorph.     

WHAT SHALL WE DO WITH THE BLUE-GREEN COUNTERPARTS?

Lichens are troublesome organisms for taxonomists because of their special ‘ double nature ’, i.e. being composed (normally) of two partners. Only recently has it been understood properly that the same fungus can take different photosynthetic partners and develop into quite different-looking organisms, for exampleLobaria amplissimaandDendriscocaulon umhausense. The taxonomic problem is to show that two totally different-looking lichens in fact contain the same fungus. This is possible to demonstrate when mixed stands are available, but is now best done with molecular methods. Since the international code of nomenclature rules that the name of a lichen species is the name of the fungus, two different organisms with the same fungus must under the Code carry the same name, which is most impractical. To remove this unintentional complication, one must either make an exception in the Code for these cases, or establish an informal system to take care of them. The latter seems to be preferable.     

PHYLOGENETIC PATTERNS AMONG NOSTOC CYANOBIONTS WITHIN BI‐ AND TRIPARTITE LICHENS OF THE GENUS PANNARIA1

Phylogenetic relationships between Nostoc cyanobionts in the lichen genus Pannaria were studied to evaluate their correlation to geography, habitat ecology, and other patterns previously reported. The 16S rRNA gene sequences of a total of 37 samples of 21 Pannaria species from seven countries from the Northern and Southern hemispheres were analyzed and compared with 69 free‐living and symbiotic cyanobacterial strains. The sequences from Pannaria were distributed throughout a branch of Nostoc sequences previously called “the Nephroma guild,” and within two subgroups from another branch, referred to as the “Peltigera guild,” although there was a gradual transition between the two major groups. There is a more diverse pattern of relationships between Nostoc sequences from bipartite versus tripartite lichen species in Pannaria, compared with other well‐studied genera, such as Nephroma and Peltigera. Cyanobionts from several tripartite Pannaria species from the Southern Hemisphere and corticolous bipartite species from both hemispheres were grouped together. Four sequences of Pannaria and Pseudocyphellaria cyanobionts from rocks in the Chilean Juan Fernández Islands were nested within corticolous cyanobionts, whereas the terricolous “Pannaria sphinctrina clade” was placed with other terricolous strains. The cluster patterns derived from phylogenetic analysis were partly reflecting lichen taxonomy, in two groups of lichen species, possibly indicating coevolution. The phylogram partly also reflected lichen ecology. Three Pannaria species have very different cyanobiont strains when they grow in different habitats.