In situ photosynthetic differentiation of the green algal and the cyanobacterial photobiont in the crustose lichen Placopsis contortuplicata

Improved monitoring of cryptogam gas-exchange and volatile emissions during desiccation-rehydration cycles with a within-chamber hydration method

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.

Impacts of Cd Pollution on the Vitality, Anatomy and Physiology of Two Morphologically Different Lichen Species of the Genera Parmotrema and Usnea, Evaluated under Experimental Conditions

The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers.

A new analysis of Mars "Special Regions": findings of the second MEPAG Special Regions Science Analysis Group (SR-SAG2)

A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.

Morphological, photosynthetic and water relations traits underpin the contrasting success of two tropical lichen groups at the interior and edge of forest fragments

BACKGROUND AND AIMS

Forest edges created by fragmentation strongly affect the abiotic and biotic environment. A rarely studied consequence is the resulting impact on non-vascular plants such as poikilohydric lichens, known to be highly sensitive to changes in the microenvironment. We evaluated the impact of forest edge and forest interior on the distribution of two groups of crustose lichens characterized by the presence or absence of a cortex and sought explanations of the outcome in terms of photosynthetic response and water relations.

METHODOLOGY

Microclimate, distribution patterns and physiology of cortical and non-cortical lichens were compared at the edge and in the interior of an Atlantic rainforest fragment in Alagoas, Brazil. Ecophysiological aspects of photosynthesis and water relations were studied using chlorophyll a fluorescence analysis, and hydration and rehydration characteristics.

PRINCIPAL RESULTS

Cortical and non-cortical functional groups showed a clear preference for interior and edge habitats, respectively. The cortical lichens retained liquid water more efficiently and tolerated low light. This explains their predominance in the forest interior, where total area cover on host tree trunks reached ca. 40 % (versus ca. 5 % for non-cortical lichens). Although non-cortical lichens exchanged water vapour efficiently, they required high light intensities. Consequently, they were able to exploit well-lit edge conditions where they achieved an area cover of ca. 19 % (versus ca. 7 % for cortical lichens). We provide some of the first data for lichens giving the relative quantity of incident light absorbed by the photosystem (absorptivity). The cortical group achieved higher absorptivity and quantum efficiencies, but at the expense of physiological plasticity; non-cortical lichens showed much decreased values of F(v)/F(m) and electron transport rates in the forest interior.

CONCLUSIONS

Morphological and physiological features largely determine the ecophysiological interaction of lichen functional groups with their abiotic environment and, as a consequence, determine their habitat preference across forest habitats. In view of the distinctiveness of their distribution patterns and ecophysiological strategies, the occurrence of cortical versus non-cortical lichens can be a useful indicator of undisturbed forest interiors in tropical forest fragments.

Are lichens active under snow in continental Antarctica?

Photosynthetic activity, detected as chlorophyll a fluorescence, was measured for lichens under undisturbed snow in continental Antarctica using fibre optics. The fibre optics had been buried by winter snowfall after being put in place the previous year under snow-free conditions. The fibre optics were fixed in place using specially designed holding devices so that the fibre ends were in close proximity to selected lichens. Several temperature and PPFD (photosynthetic photon flux density) sensors were also installed in or close to the lichens. By attaching a chlorophyll a fluorometer to the previously placed fibre optics it proved possible to measure in vivo potential photosynthetic activity of continental Antarctic lichens under undisturbed snow. The snow cover proved to be a very good insulator for the mosses and lichens but, in contrast to the situation reported for the maritime Antarctic, it retained the severe cold of the winter and prevented early warming. Therefore, the lichens and mosses under snow were kept inactive at subzero temperatures for a prolonged time, even though the external ambient air temperatures would have allowed metabolic activity. The results suggest that the major activity period of the lichens was at the time of final disappearance of the snow and lasted about 10-14 days. The activation of lichens under snow by high air humidity appeared to be very variable and species specific. Xanthoria mawsonii was activated at temperatures below -10 degrees C through absorption of water from high air humidity. Physcia dubia showed some activation at temperatures around -5 degrees C but only became fully activated at thallus temperatures of 0 degrees C through liquid water. Candelariella flava stayed inactive until thallus temperatures close to zero indicated that liquid water had become available. Although the snow cover represented the major water supply for the lichens, lichens only became active for a brief time at or close to the time the snow disappeared. The snow did not provide a protected environment, as reported for alpine habitats, but appeared to limit lichen activity. This provides at least one explanation for the observed negative effect of extended snow cover on lichen growth.

Biomonitoring air pollution with the desert lichen Ramalina maciformis

To investigate the environmental impact of anthropogenic activity in the Negev Desert, we monitored the following in order to determine the physiological integrity of the epilithic fruticose lichen Ramalina maciformis: (1) production of ethylene; (2) potential quantum yield of photosystem II expressed as chlorophyll fluorescence ratio Fv/Fm; and (3) electrolyte leakage of cell membranes in terms of electric conductivity. The degree of pollution was assessed by measuring the amounts of B, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Sr and Zn in the lichen thallus. Some of the lichen-carrying stones collected in the relatively unpolluted control site were relocated on the same hill, to test the possible impact of relocation. An additional amount of lichen-carrying stones was marked as controls. The greater part of the lichen-carrying stones was transferred to 10 biomonitoring sites in and around Ramat Hovav, an industrial area in the Negev Desert, Israel. Transplanted lichen in polluted sites contained higher amounts of mineral elements than lichens in the control site after an exposure period of 7 months. Statistical analysis revealed positive correlation of ethylene production and Ni content, negative correlation of Fv/Fm ratios and B, Cu, Mn, Na, Ni, Sr and Zn, and positive correlation of electric conductivity and B, Mn, Ni and Sr. Both elemental content and physiological alterations in transferred samples of R. maciformis point to a high degree of contamination in Ramat Hovav. The present study suggests that the lichen R. maciformis should be classified as a sensitive species endangered by anthropogenic activity in the desert. Furthermore, this lichen species is likely to be suitable as a bioindicator of pollution in other parts of the Negev Desert. Ethylene production and electric conductivity as parameters of lichen-vitality, indicated stress in 5 of the 12 biomonitoring sites (42%) and may therefore be considered as more sensitive than the Fv/Fm ratio, which indicated stress in 3 of the 12 sites (25%).

Chlorophyll fluorescence analysis of cyanobacterial photosynthesis and acclimation

Cyanobacteria are ecologically important photosynthetic prokaryotes that also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanobacteria benefit from real-time information on photosynthesis and acclimation. Monitoring in vivo chlorophyll fluorescence can provide noninvasive measures of photosynthetic physiology in a wide range of cyanobacteria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of key structural and functional properties of cyanobacteria. These include significant fluorescence emission from the light-harvesting phycobiliproteins; large and rapid changes in fluorescence yield (state transitions) which depend on metabolic and environmental conditions; and flexible, overlapping respiratory and photosynthetic electron transport chains. The fluorescence parameters FV/FM, FV'/FM',qp,qN, NPQ, and phiPS II were originally developed to extract information from the fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and used to extract biologically useful information from cyanobacterial in vivo chlorophyll fluorescence signals. We describe how the pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes. The size of the change in fluorescence yield during dark-to-light transitions can provide information on respiration and the iron status of the cyanobacteria. Finally, fluorescence parameters can be used to estimate the electron transport rate at the acclimated growth light intensity.