Carbon dioxide exchange in lichens: Relationship between the diffusive resistance of carbon dioxide and water vapour

Gaseous diffusion resistances for carbon dioxide and water vapour, thallus water content and thallus water potential were experimentally determined on species of the Stictaceae. The diffusion resistance to water loss was high only at low water contents and correlated closely with thallus water potential. Carbon dioxide diffusion resistances, however, were high at both low and high water contents and, even at medium water contents, were still an order of magnitude greater than the water resistance. These results indicate that carbon dioxide and water vapour exchange occur by different pathways in these lichens. Consequently it is suggested that the lichens have structural adaptations which separate the functions of water uptake, water storage and carbon dioxide exchange

Diel and seasonal courses of ambient carbon dioxide concentration and their effect on productivity of the epilithic lichen Lecanora muralis in a temperate, suburban habitat

Ambient CO₂ concentration (together with CO₂ exchange and microclimate) was recorded every 30 min for 15 months for Lecanora muralis growing in the Botanical Garden Würzburg (Germany, northern Bavaria), a habitat on the outskirts of the city. Annual mean CO₂ was around 17 ppm higher than the global average reported for the time of measurement (361 ppm; 1995/96), and daily values ranged from 317 to 490 ppm. Diel courses of CO₂ could be classified into three different types. Type A, when CO₂ levels rose overnight and then fell strongly to below global levels during the day, which predominated in the summer (about 75 of days); Type B, irregular diel courses occurred during all seasons with often very rapid changes apparently due to advective CO₂ transport; Type C, CO₂ concentration was typically almost stable at generally between c. 330 and 430 ppm which predominated in the winter (63 of days). Under controlled conditions, CO₂ saturation of net photosynthesis (NP) of L. muralis at optimal hydration and light occurred at around 1000 ppm. NP was also affected by low CO₂ at limiting light and thallus water contents. Based upon these data, we estimated the improvement of NP of L. muralis due to transient increase of ambient CO₂ (as compared with the global average) for one selected combination of environmental factors (nocturnal dew or frost). This combination is an important source of water for the lichen, resulting in 40 of its annual production and, especially in these situations, photosynthesis was increased by high ambient CO₂ in the early morning under prevailing Type A conditions. After dew activation, light compensation point of NP occurred at an average concentration of 413 ppm and diel maxima of NP at 402 ppm. This allows a rough estimate that the transiently elevated CO₂ increased the photosynthetic gain of the lichen after dew of 7, or an improvement to its annual carbon balance of about 3. Conditions, especially interrelationships between lichen hydration, light and CO₂ are so complex that we are not yet able to extend our estimates to other environmental situations of photosynthetic activity of L. muralis

Ecophysiological adaptations of the lichen genera pseudocyphellaria and sticta to south temperate rainforests

Temperate rainforests are a poorly researched habitat with respect to lichen ecophysiology in comparison to desert and polar regions. The evergreen, broadleaf forests provide a dim, moist environment that is relatively stable throughout the year. Lichens are abundant in both quantity and species diversity with the large foliose genera Sticta and Pseudocyphellaria normally being dominant, visually and in terms of biomass. These lichens exhibit a great diversity of both form and habitat range. Physiological and morphological adaptation has also been demonstrated. Pseudocyphellaria dissimilis shows changes in thallus water storage capacity with evaporative demand and is also highly shade-adapted. The species has the lowest light saturation and compensation values for photosynthesis yet known for lichens (20 and 1-μmol m−2s−1, PAR, respectively). Unexpectedly it is also highly desiccation-sensitive with some thalli being killed after only 20 h exposure to 15% relative humidity. Photobiont versatility is also a feature of these genera. Photosymbiodemes occur, i.e. a single thallus containing both green algal and cyanobacterial sectors. Because the different sectors have the same fungal partner and grow in the same habitat, it is possible to investigate whether particular physiological traits are photobiont determined. The ability to recover photosynthetic activity in humid air is confined to thalli with green algal photobionts whilst the inability of thalli containing cyanobacterial photobionts to tolerate high light stress may be related to their lack of a protective xanthophyll cycle

A provisional survey of the interaction between net photosynthetic rate, respiratory rate, and thallus water content in some New Zealand cryptogams

The effect of water content on photosynthetic and respiratory rates in eight lichen species and one bryophyte species were studied using an injection infrared gas analyser technique. All species snowed a strong relationship between net assimilation rate (NAR), respiration rate, and water content similar to relationships reported in published studies overseas. Species from moist habitats showed negative NAR at low water contents. Species from high-light areas showed a depression in NAR at high water contents which could be alleviated by higher light intensities. The experiments confirmed the suitability of New Zealand species for these studies

An unusual growth form of Cladonia furcata: The trampling-resistant primary thallus colonizing a paved pathway

Lichens are well known to be susceptible to damage by trampling. Fruticose species, with their highly branched structure, are particularly sensitive and Bayfield et al. (1981) described substantial damage to Cladonia uncialis, C. arbuscula, C. rangiferina, and C. impexa on paths in lichen-rich heath communities in north-east Scotland. Less visible communities, biotic soil crusts in arid and semi-arid areas with their cover of crustose lichens, are also easily disturbed by walking, car driving, or grazing and recovery can take decades. We report here an interesting situation where a lichen (Cladonia furcata) is apparently being maintained and even spread in a habitat because trampling prevents it from completing its monocarpic life cycle

Spatial modelling of wetness for the Antarctic Dry Valleys

This paper describes a method used to model relative wetness for part of the Antarctic Dry Valleys using Geographic Information Systems (GIS) and remote sensing. The model produces a relative index of liquid water availability using variables that influence the volume and distribution of water. Remote sensing using Moderate Resolution Imaging Spectroradiometer (MODIS) images collected over four years is used to calculate an average index of snow cover and this is combined with other water sources such as glaciers and lakes. This water source model is then used to weight a hydrological flow accumulation model that uses slope derived from Light Detection and Ranging (LIDAR) elevation data. The resulting wetness index is validated using three-dimensional visualization and a comparison with a high-resolution Advanced Land Observing Satellite image that shows drainage channels. This research demonstrates that it is possible to produce a wetness model of Antarctica using data that are becoming widely available

Extreme southern locations for moss sporophytes in Antarctica

Abundant immature sporophytes of the moss Pottia heimii are reported from the Lower Taylor Valley, McMurdo Dry Valleys and from Cape Chocolate, Victoria Land. These finds extend the reported southern limit for the occurrence of abundant moss sporophytes to 77° 55′S

Diversity of Lecidea (Lecideaceae, Ascomycota) species revealed by molecular data and morphological characters

The diversity of lichens, especially crustose species, in continental Antarctica is still poorly known. To overcome difficulties with the morphology based species delimitations in these groups, we employed molecular data (nuclear ITS and mitochondrial SSU rDNA sequences) to test species boundaries within the genus Lecidea. Sampling was done along a north–south transect at five different areas in the Ross Sea region (Cape Hallett, Botany Bay to Mount Suess, Taylor Valley, Darwin Area and Mount Kyffin). A total of 153 specimens were collected from 13 localities. Phylogenetic analyses also include specimens from other regions in Antarctica and non-Antarctic areas. Maximum parsimony, maximum likelihood and Bayesian analyses agreed in placing the samples from continental Antarctica into four major groups. Based on this phylogenetic estimate, we restudied the micromorphology and secondary chemistry of these four clades to evaluate the use of these characters as phylogenetic discriminators. These clades are identified as the following species Lecidea cancriformis, L. andersonii as well as the new species L. polypycnidophora Ruprecht & Türk sp. nov. and another previously unnamed clade of uncertain status, referred to as Lecidea sp. (L. UCR1)

Isolation and characterization of microsatellites in the lichen Buellia frigida (Physciaceae), an Antarctic endemic

Premise of the study: Microsatellite markers were characterized for an Antarctic endemic, Buellia frigida, to investigate population structure and origin of Antarctic lichens. Methods and Results: Five primer sets were characterized. All loci were polymorphic with eight to 16 alleles per locus in a sample of 59 lichens. Conclusions: The microsatellite markers potentially provide insight into population structure and gene flow of B. frigida

Rainfall as a cause of mechanical damage to Pseudocyphellaria rufovirescens in a New Zealand temperate rainforest

Lichens, like all poikilohydric plants, have a metabolism that is dependent on external moistening from their environment. In the case of green algal lichens high humidities may be sufficient for positive net photosynthesis to occur (Lange et al. 1993a). For these plants water stress is usually taken to mean a lack of water (Kappen 1988; Rundel 1988) but it can also mean an excess of water that leads to depressed CO2 exchange because of increased diffusion resistances at high thallus water contents (Lange & Tenhunen 1981; Kershaw 1985). Rather than this being an unusual occurrence, Lange et al. (19936) found reduced CO2 exchange at thallus supra-saturation to be present over long periods in the temperate rainforest of north-eastern New Zealand